The proof comes back with three notes from the printer's prepress team: the 2 % highlight in the gradient will not hold at 133 lpi, the reversed white text needs a spread, and the brand red sits outside the CMYK gamut, so it should run as a spot colour or be built in extended gamut. Each note affects cost, appearance or schedule, and the person approving the artwork has to understand it to make the right call. This printing terms glossary defines the vocabulary used on packaging print quotations, prepress reports, proofs and press approvals, from anilox volume and plate distortion to Delta E, G7 and the names of common print defects.
How to use this printing terms glossary
The page is written for packaging buyers, designers, quality managers and packaging engineers who approve artwork and printed samples but do not run presses themselves. Each entry gives a definition, how the property works or is measured with typical values where they are meaningful, and what it changes for the buyer: cost, colour, legibility or food-contact suitability. Typical values are labelled as such because presses, plates, inks and substrates vary; the figures for any specific job are set by the printer and confirmed at quotation and technical review.
Headings give the English term first, then abbreviations and the German (DE) or Dutch (NL) term where it is in common use in supplier correspondence. Entries are alphabetical within each section. Where a topic has its own guide on this site, the entry links to it for depth.
This page is part of the packaging glossary. The sibling glossaries cover converting and manufacturing terms, packaging materials, testing, quality and defects and regulation, sustainability and trade. Finishing effects such as foil, embossing and lamination are defined in the converting and materials glossaries; only print varnishes are covered here.
Printing processes and press types
How the image reaches the substrate, and the press configurations that appear on packaging quotations. Process selection by product and run length is covered in flexo vs offset vs gravure vs digital printing.
Central impression flexo press (CI press)
A central impression press arranges all flexo colour stations around one large, temperature-controlled impression drum, so the web stays in contact with the same drum from the first colour to the last. Because the web cannot stretch or wander between stations, registration is very stable, which is why CI presses dominate flexo printing on thin, extensible films and on paper for bags and wraps. CI presses commonly carry six to ten colour stations and print one side of the web per pass.
Digital printing (DE: Digitaldruck; NL: digitaal drukken)
Digital printing creates the image directly from the file, by inkjet or by toner, with no plates or cylinders. Set-up cost is minimal and each piece can differ, but the running cost per unit stays relatively flat as quantity rises, so digital is strongest for short runs, prototypes, printed samples and versioned designs. Spot colours are usually simulated from the press's ink set rather than mixed, and the ink system has to be checked for food-packaging use like any other.
See: flexo vs offset vs gravure vs digital printing
Dry offset (DE: Trockenoffset)
Dry offset prints pre-formed round containers, such as plastic cups, tubs and lids, by inking relief plates that transfer each colour onto a single shared blanket, which then rolls the complete image onto the rotating container. "Dry" means no fountain solution is used, unlike offset lithography. Because all colours meet wet on one blanket, they cannot be overprinted cleanly, so designs are built with colours side by side and with halftones rather than true trapping or overprints. Paper cups are not printed this way; they are printed flat before forming.
See: paper cup printing
Electrophotography (toner printing; liquid or dry toner)
Electrophotography is the digital process in which a laser or LED writes the image as an electrostatic charge on a drum, charged toner particles are attracted to the image, and the toner is transferred and fused to the substrate. Dry toner and liquid toner versions are both used in packaging, the latter mainly for folding cartons, labels and flexible packaging on short runs. Image quality on suitable substrates is close to offset; speed and maximum format are lower than conventional presses.
Flexography (flexo; DE: Flexodruck; NL: flexodruk)
Flexography prints from raised, flexible photopolymer plates inked by an engraved anilox roll and transfers the ink directly to the substrate. It runs fast on reels and on corrugated board, works with water-based, solvent-based and UV inks, and is the dominant process for paper bags, wraps, napkins, plastic film and corrugated packaging. Modern high-definition plates and flat-top dots have narrowed the quality gap with offset, especially on film.
See: flexo vs offset vs gravure vs digital printing
Gravure (rotogravure; DE: Tiefdruck; NL: diepdruk)
Gravure prints from metal cylinders engraved with millions of small cells, one cylinder per colour; the cells fill with low-viscosity ink, a doctor blade wipes the surface clean and the substrate picks the ink out of the cells under pressure. Colour is rich and very stable over long runs, but engraved cylinders are expensive, so gravure pays off on long runs of unchanged designs, mostly on film for laminated flexible packaging.
See: flexo vs offset vs gravure vs digital printing
Hybrid printing
Hybrid printing combines two print technologies in one production line, most often a digital inkjet unit integrated into a flexo or offset press, so static elements print conventionally while variable or versioned elements print digitally in the same pass. The term is also used for presses that mix flexo, screen or other units, and for "hybrid" UV inks or hybrid screening, so it is worth asking which meaning a supplier intends.
Inkjet printing (single-pass, multi-pass)
Inkjet printing fires tiny droplets of ink from print-head nozzles directly onto the substrate under digital control. Single-pass presses print the full width in one pass under fixed heads and suit industrial packaging volumes; multi-pass (scanning) printers move the heads back and forth and are slower, used mainly for samples and very short runs. Water-based and UV inkjet inks are common in packaging, and food-packaging suitability depends on the specific ink system and its documentation.
Inline flexo press
An inline flexo press has its colour stations in a horizontal row, each with its own impression cylinder, with the web or sheet travelling from one to the next. The layout gives easy access and suits thicker substrates such as board, and it allows converting operations like die-cutting, varnishing or laminating in the same line. Narrow-web label presses and many cupstock and carton flexo lines use this configuration.
Letterpress (DE: Buchdruck; NL: boekdruk)
Letterpress prints from rigid raised plates with paste-like inks, applied with light "kiss" pressure. Once the main commercial process, it now has a small share of packaging print, mainly UV letterpress on narrow-web self-adhesive labels and some cup and lid lines. It is the relief process from which flexography and dry offset developed.
Narrow web and wide web
Narrow web and wide web describe the width of reel-fed presses. Narrow-web presses, generally below about 500 mm (20 in) print width, are typical for labels and short-run flexible packaging; wide-web presses, often well above 1,000 mm, print film and paper for bags, wraps and pouches at volume. Definitions vary between suppliers, and the press width matters to a buyer mainly because it limits how many items can be printed across the web.
Offset lithography (offset, litho; DE: Offsetdruck; NL: offsetdruk)
Offset lithography prints from flat plates on which the image areas attract greasy ink and the non-image areas attract water, transferring the inked image to a rubber blanket and from the blanket to the sheet or web. It gives the sharpest detail and smoothest gradients of the common processes and is the standard for folding cartons, cup blanks and litho-laminated corrugated liners. "Litho" is the usual UK trade shorthand.
See: flexo vs offset vs gravure vs digital printing
Post-print and pre-print (corrugated printing)
Post-print means printing directly onto finished corrugated board, usually by flexo in one to three colours, while pre-print means printing the liner on reels, by flexo or gravure, before it is combined with fluting on the corrugator. Pre-print gives smoother tones and suits very large runs; post-print is the norm for pizza boxes, shipping boxes and most mailers. A third route, litho-lamination, glues an offset-printed sheet onto corrugated for photographic quality.
See: pizza box printing
Reverse printing and surface printing
Surface printing places the ink on the outside of a substrate, where it is seen directly; reverse printing places it on the inside of a transparent film so it is seen through the film, usually before the film is laminated to another layer. Reverse-printed artwork is mirrored and the white is printed last, behind the colours, and the ink ends up protected inside the laminate, away from both the consumer and the food. Most laminated pouches are reverse printed; carrier bags are usually surface printed.
Screen printing (DE: Siebdruck; NL: zeefdruk)
Screen printing pushes ink through a fine mesh stencil onto the substrate, laying down a much thicker ink film than flexo or offset. It gives opaque whites, bold colour on dark or textured materials and tactile or raised effects, and rotary screen units are sometimes added to label and carton lines for these effects. It is slow and suited to simple, few-colour designs, so it is rarely the main process for disposable foodservice packaging.
See: flexo vs offset vs gravure vs digital printing
Sheet-fed offset
Sheet-fed offset feeds individual cut sheets through the press, typically with four process units plus one or two spot-colour units and an inline coating unit for varnish or aqueous coating. Several items are imposed on each sheet and die-cut afterwards. It is the standard route for folding cartons, burger and takeaway boxes in board, cup blanks and litho-lam liners, where fine type and photographic images matter.
See: flexo vs offset vs gravure vs digital printing
Stack flexo press
A stack press has its flexo colour stations arranged one above the other on one or both sides of a vertical frame, each with its own impression cylinder. It is compact and can print both sides of the web in one pass, but registration on stretchy films is less precise than on a CI press because the web travels freely between stations. Stack presses are common for paper bags, wrapping papers and simpler film work.
Web offset (variable-sleeve offset)
Web offset prints by offset lithography on a continuous reel rather than on sheets. Variable-sleeve web offset presses change the plate and blanket sleeves to alter the print repeat, which makes the process usable for flexible packaging, labels and cupstock reels, often with UV or EB-curing inks. It competes with gravure and flexo where offset-quality images and frequent design changes are needed.
Flexo press, anilox and plate terms
The components that control how much ink a flexo press lays down and how sharply it prints. These terms explain why flexo quotations list plate costs, why fine images and solid colours compete for the same anilox, and why repeat length is fixed by the press.
Anilox cell count (screen count; lines per inch, lines per cm)
Anilox cell count is the number of engraved cells per linear inch or centimetre on an anilox roll's surface. Packaging work typically uses from about 200 lines per inch (80 per cm) for heavy coatings, whites and corrugated up to 1,000 lines per inch (about 400 per cm) or more for fine process work on film. A common rule is that the anilox count should be at least four to six times the screen ruling of the plate, so the smallest dots are supported by several cells instead of dipping into one.
Anilox roll (DE: Rasterwalze; NL: aniloxrol)
An anilox roll is an engraved metal or ceramic-coated roll in a flexo press whose cell count and cell volume meter a precise, even film of ink onto the printing plate. Most modern anilox rolls are laser-engraved ceramic with hexagonal cells at 60°, which wear slowly and can be cleaned thoroughly. Fine rolls with small cells suit halftones and detail, coarse high-volume rolls lay heavy solids and whites, and a worn or partially plugged anilox is a frequent cause of colour drift between runs.
See: flexo vs offset vs gravure vs digital printing
Anilox volume (BCM; cm³/m²)
Anilox volume is the volume of ink an anilox roll's cells can carry per unit area, expressed in the US as BCM (billion cubic microns per square inch) and in Europe as cm³/m², where 1 BCM is about 1.55 cm³/m². Typical values run from roughly 1 to 2.5 BCM for halftone work, 3 to 5 BCM for line work and solids, and higher for opaque whites, coatings and corrugated. Volume largely determines the ink film thickness and therefore the strength of solid colours; specifying the anilox together with the ink is how flexo colour is kept repeatable on reorders.
Chambered doctor blade (DE: Kammerrakel)
A chambered doctor blade is an enclosed ink-feed system in which two blades, one doctoring and one containment blade, form a sealed chamber against the anilox roll, with ink pumped through it. It keeps ink in a closed loop, which reduces solvent evaporation and viscosity drift, limits foaming and allows faster colour changes. It is the standard inking system on modern flexo presses for packaging.
Doctor blade (DE: Rakel; NL: rakel)
A doctor blade is a thin steel, plastic or composite blade pressed against an inked roll or cylinder to wipe off excess ink, leaving ink only in the engraved cells. In flexo it scrapes the anilox surface so that a metered volume reaches the plate; in gravure it wipes the cylinder so ink stays only in the image cells. Blade angle, pressure and wear affect ink film consistency, and a damaged blade shows up as fine streaks along the direction of print.
Flat-top dots
Flat-top dots are flexo plate dots with a flat printing surface and sharp shoulders, instead of the rounded tops produced by conventional digital plate exposure, where oxygen in the air limits curing of the smallest dots. They are made with oxygen-barrier or high-intensity LED exposure systems and hold smaller highlight dots, give more stable dot gain under pressure changes and often carry surface screening for denser solids. For buyers, flat-top plates usually mean smoother vignettes and better fine detail, at a somewhat higher plate cost.
Impression (impression setting)
Impression is the contact pressure between the plate and the substrate, and between the anilox and the plate, set by the positions of the plate cylinder and anilox relative to the impression cylinder. Flexo should run at the lightest impression that transfers a full image; excess impression squeezes ink to the edges of plate elements, enlarging dots, causing halos and filling in reversed type. Impression settings are adjusted at make-ready and can drift with plate wear, tape compression and substrate thickness.
Kiss impression
Kiss impression is the minimum contact pressure at which the plate just transfers a complete, even image to the substrate, without visible squash. It is the target setting for flexo and letterpress because it keeps dot gain lowest and fine detail open. On rough or fluted substrates such as kraft paper and corrugated board, slightly more impression is often needed to reach the low points of the surface.
Mounting tape (compressible plate-mounting tape; DE: Klischeeklebeband)
Mounting tape is a double-sided adhesive tape with a compressible foam core used to fix flexo plates to a cylinder or sleeve, typically about 0.38 to 0.55 mm thick. Its foam density changes the print: softer tapes cushion the plate and reduce dot gain in halftones, harder tapes give better ink laydown in solids, and medium tapes are used where a plate carries both. Mounting accuracy and tape choice are part of why repeat jobs on remounted plates can print slightly differently.
Photopolymer plate (flexo plate, cliché; DE: Klischee; NL: cliché)
A photopolymer plate is the flexible relief printing plate used in flexo, made from a light-sensitive polymer layer on a polyester base that is imaged, exposed to UV light and processed with solvent, water or heat to leave the image areas raised. Common thicknesses are 1.14 mm for film and narrow web and 1.70 mm for paper and wide web, with thicker, softer plates of roughly 3 to 7 mm for corrugated post-print. Plates are a one-off cost per colour and design, shown as Klischeekosten in German quotations, and can be stored and reused on repeat orders if the artwork does not change.
See: flexo vs offset vs gravure vs digital printing
Plate cylinder
The plate cylinder is the cylinder in a flexo press that carries the mounted plates, either directly or via a sleeve, and transfers ink from the plate to the substrate on each revolution. Its circumference, together with the plate and tape thickness, fixes the print repeat length, so each press has a set of available repeats. A design whose length does not fit an available repeat needs a different cylinder or sleeve, or an adjusted layout.
Plate distortion (distortion factor)
Plate distortion is the stretching of a flexo plate's printing surface in the around-the-cylinder direction when the flat plate is wrapped onto the cylinder or sleeve. Prepress compensates by shortening the image in that direction by a distortion factor, which depends on plate thickness and repeat length and is commonly in the order of one to a few percent. Without compensation, the printed image comes out longer than the artwork, which matters for bag lengths, panel positions and barcodes.
Sleeve (plate sleeve, bridge sleeve)
A sleeve is a lightweight cylindrical tube onto which flexo plates are mounted, slid over an air mandrel on the press instead of changing heavy steel cylinders. Bridge or adapter sleeves build up the mandrel diameter so that different repeat lengths can run on the same press. Sleeves speed up job changes and allow plates to be mounted off-press and stored ready for repeat orders.
Surface screening (microcell screening)
Surface screening is a very fine pattern of tiny cells or textures imaged into the solid areas of a flexo plate. The pattern breaks the smooth plate surface so that it carries and releases ink more evenly, giving higher solid ink density and less mottle and pinholing, particularly on film. It is applied in prepress or plate-making and does not change the artwork the buyer supplies.
Gravure terms
The vocabulary of gravure cylinders and how they hold ink. Relevant mainly to laminated pouches and other long-run flexible packaging.
Cell depth and cell volume (gravure)
Cell depth is how deep each engraved cell in a gravure cylinder is, and cell volume is how much ink it holds; together with cell opening, they determine how much ink each area prints. Depths typically range from a few micrometres in highlights to around 40 micrometres or more in solids, and varying cell size and depth is how gravure produces tone without visible halftone dots. Cell volume is fixed once the cylinder is engraved, which is the reason gravure colour is so stable over long runs.
Chrome plating (gravure cylinders)
Chrome plating is a thin layer of hard chromium, a few micrometres thick, electroplated onto the engraved copper surface of a gravure cylinder. It protects the soft copper from doctor-blade wear so the cylinder can print very long runs, and worn cylinders can be dechromed, repaired and replated. Some suppliers offer alternative hard coatings in response to restrictions on hexavalent chromium plating.
Doctor blade (gravure)
In gravure, the doctor blade wipes all ink from the smooth, non-image surface of the engraved cylinder while leaving ink in the cells. Because gravure prints directly from the cylinder, blade setting is critical: a worn or nicked blade leaves fine lines of ink on the print (doctor streaks), and a poorly set blade can leave a faint film of ink over non-image areas (hazing). Blade angle and pressure are part of press set-up rather than buyer specification, but streak defects are a common reason for rejected gravure reels.
Electromechanical engraving
Electromechanical engraving cuts the cells of a gravure cylinder with a diamond stylus that oscillates at high frequency, controlled by the digital image data, producing thousands of cells per second. Cell size and depth vary together with the tone value. It is the most widely used gravure engraving method, and engraving is a significant part of the cost of a gravure cylinder set.
Electrostatic assist (ESA)
Electrostatic assist is a system that applies an electrical charge between the gravure impression roller and the cylinder so that ink is drawn out of the cells onto the substrate. It reduces missing dots, the speckled appearance that occurs when rough or less compressible substrates fail to contact every cell. It is used particularly on paper and board and in highlight areas.
Gravure cylinder (DE: Tiefdruckzylinder)
A gravure cylinder is the steel or aluminium base cylinder, plated with copper, engraved with the image cells and finished with chrome, that carries one colour in gravure printing. Its circumference fixes the print repeat and its face width the maximum print width. Cylinders are expensive to make but last for very long runs and can be stored for repeat orders, which is why gravure suits stable, long-running designs.
Laser engraving (gravure)
Laser engraving creates gravure cells either by ablating a mask on the cylinder before chemical etching or by directly laser-engraving a suitable cylinder surface. It allows cell shapes and edges that electromechanical engraving cannot, such as very sharp text and line work, and is often used where fine type and vector elements matter. Which method is used is the cylinder maker's choice, but it can affect how fine detail reproduces.
Offset lithography terms
Offset depends on the balance between water and ink on the plate. These terms appear in press reports and in discussions about colour consistency on cartons and cups.
Blanket (DE: Gummituch; NL: rubberdoek)
A blanket is the rubber-surfaced fabric sheet wrapped around the blanket cylinder of an offset press, which receives the inked image from the plate and transfers it to the sheet. Its compressibility lets the image reach the substrate evenly even on slightly uneven board. A damaged or smashed blanket prints a local defect on every sheet until it is replaced, and blanket condition affects dot gain.
Computer-to-plate (CTP)
Computer-to-plate is the process of imaging printing plates directly from digital data by laser, without film. In offset, CTP plates are aluminium with a light- or heat-sensitive coating; in flexo, the equivalent is digital photopolymer plate imaging. CTP gives sharp, repeatable dots and allows printers to remake offset plates cheaply, which is why offset plates are often treated as consumables rather than stored tooling.
Fountain solution (dampening solution, damping solution UK; DE: Feuchtmittel)
Fountain solution is the water-based solution applied to an offset plate to keep the non-image areas wet so they repel ink. It is typically slightly acidic, around pH 4.5 to 5.5, and contains additives that control surface tension and conductivity; isopropyl alcohol has traditionally been added, and reduced-alcohol or alcohol-free systems are increasingly common to cut emissions. Its condition affects ink-water balance, drying and print stability.
Ink-water balance
Ink-water balance is the equilibrium on an offset press between the amount of ink and the amount of fountain solution on the plate. Too much water emulsifies the ink, dulls colours and slows drying; too little lets ink spread into non-image areas, a defect called scumming or toning. Keeping the balance stable through a run is one of the main factors in offset colour consistency.
Offset plate (aluminium plate)
An offset plate is a thin aluminium plate with a grained, treated surface and an imaged coating, on which image areas accept ink and non-image areas accept water; there is no relief. One plate is needed per colour, including spot colours and sometimes a varnish. Offset plates cost far less than flexo plates or gravure cylinders, so a design change mainly costs make-ready time rather than tooling.
Inks, drying and curing
Ink chemistry decides adhesion, rub resistance, odour and food-contact suitability. The ink rules that apply to printed food packaging are summarised in food-contact packaging compliance.
Blocking (DE: Verblocken)
Blocking is unwanted sticking between surfaces of printed material in a reel or stack, so that layers adhere or the ink lifts off when separated. Causes include incompletely dried or cured ink, retained solvent, excessive heat or pressure in storage and over-treated film. It is checked with a block test, in which printed samples are pressed together under heat and pressure, and it matters most for film bags and printed reels stored in warm conditions.
Corona treatment (DE: Coronabehandlung)
Corona treatment exposes a plastic film surface to a high-voltage electrical discharge, which oxidises it and raises its surface energy so that ink and adhesives wet and bond. It is essential for printing polyethylene and polypropylene. The effect decays over time as additives migrate to the surface, so film stored for weeks may need re-treating before printing, and both sides must be treated if both are printed.
Drying and curing
Drying turns a liquid ink film into a solid one by removing water or solvent through evaporation and absorption, or, for oxidative offset inks, by absorption and oxidation; curing turns it solid by a chemical reaction triggered by ultraviolet light or an electron beam. Water-based and solvent-based flexo and gravure inks dry with hot air between and after stations, while UV and EB inks cure almost instantly. Incomplete drying or curing is a root cause of set-off, blocking, odour and migration, so drying capacity often limits press speed and ink coverage.
Dyne level (surface energy; dyn/cm, mN/m)
The dyne level is the surface energy of a substrate, expressed in dyn/cm (numerically equal to mN/m), which indicates whether ink will wet and bond to it. Untreated polyethylene is typically around 30 to 31 dyn/cm, and printers usually aim for roughly 38 to 42 dyn/cm or more after corona treatment, with water-based inks needing the upper end. It is checked with dyne test pens or test inks before printing.
EB-curable ink (electron beam; DE: ESH-Farbe)
An EB-curable ink is cured by a beam of electrons, which polymerises the ink film instantly without the photoinitiators that UV inks need. Curing is usually carried out under nitrogen to prevent oxygen interfering with the reaction. EB inks and coatings are used in offset and flexo for flexible packaging and cartons where high resistance and low migration are required, because there are no photoinitiator residues; the equipment is expensive and found on a limited number of lines.
Ink coverage
Ink coverage is the share of the printed area covered by ink, and by extension the total amount of ink laid down on a design. High coverage, such as large solids or full-bleed images, uses more ink, needs more drying, raises the risk of set-off, curl and show-through on thin papers and can affect recyclability assessments. Converters often review heavy-coverage designs on wraps and tissue before quoting and may suggest a lighter pattern.
See: printing on greaseproof paper
Ink trapping (wet trapping; DE: Farbannahme)
Ink trapping, in the press sense, is the ability of an already printed ink film to accept the next ink printed on top of it. Poor trapping makes overprinted colours, such as red built from magenta and yellow, look weak or mottled. It is measured with a densitometer and expressed as an apparent trap percentage, commonly using the Preucil formula. Not to be confused with prepress trapping, which is a deliberate overlap of adjacent colours (see Trapping under Prepress and artwork).
Low-migration ink (DE: migrationsarme Druckfarbe)
A low-migration ink is an ink system formulated and applied so that migration of its components into food stays below applicable limits under the intended conditions of use. It is not a single legal status: suitability is assessed for the specific application, typically with reference to EuPIA guidance and the Swiss Ordinance SR 817.023.21 (Annex 10), and the ink must be correctly dried or cured, under good manufacturing practice as required by Regulation (EC) 2023/2006 in the EU. From 1 January 2027, Germany's Printing Ink Ordinance adds a positive list for substances in inks on food-contact materials.
See: food-contact packaging compliance
Mineral-oil-free ink (DE: mineralölfreie Druckfarbe)
A mineral-oil-free ink is an ink formulated without mineral oil components, mostly relevant to oxidative sheet-fed offset inks, which traditionally used mineral oil distillates and now commonly use vegetable oil derivatives instead. Buyers specify it because mineral oil hydrocarbons (MOSH and MOAH) can migrate from packaging into food. It removes the ink as a source but does nothing about mineral oil already present in recycled fibre, which needs a barrier or virgin board.
See: mineral oil barriers and food-safe cartons
Pigment
A pigment is a finely ground, insoluble colouring particle dispersed in the ink's binder; it gives the ink its colour, strength and resistance to light and solvents. Packaging inks are almost entirely pigment-based, while dyes, which dissolve in the vehicle, are used in some inkjet inks and special applications. Pigment choice limits which Pantone colours can be mixed with a given ink range and affects lightfastness, opacity and price.
Retained solvent
Retained solvent is the small amount of organic solvent left in printed and laminated film after drying, measured by gas chromatography and usually expressed in mg/m². High retained solvent can cause odour, taint, blocking and weak lamination bonds, so solvent-printed flexible packaging for food is commonly released against an agreed limit. It is mainly a concern with solvent-based flexo and gravure on film.
Set-off (DE: Abliegen)
Set-off is the unwanted transfer of ink from the printed surface of one sheet or web layer onto the back of the next in a stack or reel. On food packaging it is a food-safety issue as well as a cosmetic one, because ink can reach the food-contact side; Regulation (EC) 2023/2006 requires that inks on the non-food side are not transferred to the food-contact side, through the substrate or by set-off, in amounts that would breach the food-contact requirements. Converters control it through ink selection, drying, ink coverage, reel tension and stack pressure.
See: printing on greaseproof paper
Solvent-based ink
A solvent-based ink uses organic solvents, such as ethanol, ethyl acetate or similar blends, as its liquid vehicle, typically with nitrocellulose, polyurethane or polyamide binders in flexo and gravure. It dries fast, wets low-energy film easily and gives strong adhesion, gloss and density, but releases volatile organic compounds that must be extracted and treated. It remains widely used for printing film and laminated flexible packaging.
UV-curable ink (UV ink, LED-UV; DE: UV-Farbe)
A UV-curable ink contains monomers, oligomers and photoinitiators that polymerise almost instantly when exposed to ultraviolet light, rather than drying by evaporation. LED-UV systems cure with narrow-band light, typically around 365 to 395 nm, using less energy and heat than mercury lamps. UV inks give high gloss, rub resistance and fast handling; for food packaging, residual photoinitiators and monomers can migrate, so low-migration UV systems and full curing are required.
Viscosity (DE: Viskosität)
Viscosity is a liquid ink's resistance to flow, which controls how much ink an anilox or gravure cell picks up and releases and how the ink spreads on the substrate. Flexo and gravure inks are liquid and are measured with flow cups in seconds, while offset inks are pastes characterised by tack and rheology. Viscosity rises as solvent or water evaporates during a run, so presses add diluent to hold a target; uncontrolled viscosity is a classic cause of colour drift in flexo.
Water-based ink (DE: wasserbasierte Druckfarbe)
A water-based ink uses water as the main liquid vehicle, with acrylic or similar binders and small amounts of amines or co-solvents to keep the resins dissolved, controlled through pH. It has low emissions and odour and is the standard for flexo on paper bags, wraps, napkins and corrugated board. On film it dries more slowly, usually needs higher surface treatment and more drying capacity, and can be slightly less glossy than solvent-based ink.
See: printing on greaseproof paper
Zahn cup (viscosity cup; DE: Auslaufbecher)
A Zahn cup is a small dip cup with a calibrated hole in its base, used at the press to measure liquid ink viscosity as the number of seconds the cup takes to empty, described in ASTM D4212. Cups are numbered by orifice size, with Zahn #2 common for flexo inks; in Europe DIN 4 mm and ISO flow cups (ISO 2431) are also widely used. Readings are only comparable on the same cup type at the same ink temperature.
Colour standards and measurement
How colour is specified, measured and held within tolerance. The buyer's decisions on spot colours, CMYK and tolerances are explained in Pantone vs CMYK in packaging.
CIELAB (Lab, L*a*b*)
CIELAB is the colour space, defined by the International Commission on Illumination (CIE) in 1976, that describes any colour with three values: L* for lightness, a* for the red-green axis and b* for the yellow-blue axis. It is device-independent, so a Lab value measured on an approved sample can be given to any printer as a numerical target. Delta E tolerances are calculated as distances between Lab values.
See: Pantone vs CMYK in packaging
CMYK (process colours; four-colour process; DE: Skalenfarben)
CMYK is the four-colour printing process that uses cyan, magenta, yellow and black inks, printed as halftone dots, to reproduce a wide range of colours and images. It reproduces photographs efficiently, but it matches brand colours only approximately, varying with substrate, dot gain and ink balance. Many packaging designs combine CMYK images with one or two spot colours for logos.
See: Pantone vs CMYK in packaging
Colour gamut
A colour gamut is the full range of colours a printing process, ink set and substrate combination can reproduce. CMYK on coated board has a wider gamut than CMYK on uncoated kraft, and many saturated brand colours, such as some oranges, greens and blues, lie outside any CMYK gamut. An out-of-gamut colour has to be printed as a spot colour, built in extended gamut or accepted as an approximation.
Colour profile (ICC profile)
A colour profile is a data file, in the format standardised by the International Color Consortium (ICC), that describes how a device or printing condition reproduces colour, linking its CMYK or RGB values to device-independent Lab values. Prepress uses profiles to convert images to the target printing condition and to simulate it on proofs and screens. Supplying artwork in the wrong profile, or in RGB, is a common cause of colour that looks right on screen and wrong in print.
Delta E (ΔE; colour difference)
Delta E (ΔE) is a single number expressing the difference between two colours, calculated from spectrophotometer measurements in the CIELAB colour space; the lower the number, the closer the match. Packaging tolerances are agreed between buyer and printer rather than fixed by law, often around 2 to 4 ΔE00 for spot colours depending on substrate and importance. The formula must be stated with the tolerance, because the older ΔE76 and the newer ΔE2000 give different values for the same pair of colours.
See: Pantone vs CMYK in packaging
Delta E 2000 (ΔE2000, ΔE00, CIEDE2000)
ΔE2000 is the colour-difference formula published by the CIE in 2001 that adjusts the simple Lab distance of ΔE76 for lightness, chroma and hue, so that the same number corresponds more closely to the same visible difference across the colour range. As a rough guide, about 1 ΔE00 is close to the limit a trained eye can see under controlled lighting and around 2 is noticeable side by side. It is the recommended formula for packaging colour tolerances.
See: Pantone vs CMYK in packaging
Densitometer (DE: Densitometer)
A densitometer measures optical density, the light-absorbing strength of a printed ink film, through filters matched to the process inks, using status E (common in Europe) or status T (common in the US) responses. Printers use it on press to control solid ink density, dot gain, ink trapping and print contrast. It measures ink film strength rather than colour, so it controls a known ink well but cannot judge whether a spot colour matches its target; that needs a spectrophotometer.
Extended colour gamut (ECG; CMYK+OGV, seven-colour printing)
Extended colour gamut printing adds fixed process inks, usually orange, green and violet (CMYK+OGV), to reproduce a much wider range of colours, including many brand spot colours, from one standard ink set. Instead of mixing a new spot ink for each design, colours are built from the seven inks, which cuts ink changes and wash-ups when many designs run on one press. It suits flexible packaging and labels with many SKUs; for a single critical brand colour, a true spot ink is still the safer specification.
See: Pantone vs CMYK in packaging
Fogra (Fogra characterisation data, FOGRA39, FOGRA51)
Fogra is the German graphic technology research association that publishes characterisation data sets describing standard printing conditions, which are used to build the ICC profiles common in European prepress. FOGRA39 describes sheet-fed offset on coated paper under the 2004 edition of ISO 12647-2, while FOGRA51 and FOGRA52 describe coated and uncoated paper under the 2013 edition. A file prepared for a stated Fogra condition, and proofed to it, gives printer and buyer a shared colour reference for CMYK work.
G7
G7 is a calibration method, published by Idealliance, that adjusts a printing system so that its gray balance and neutral tonality match a defined target, making different presses, processes and proofs look visually similar. It is widely used in the US and increasingly in packaging, where it helps align flexo, offset and digital output for the same brand. A printer can be qualified as a G7 Master facility, but the method aligns overall appearance; it does not replace agreed spot colour targets.
Gray balance (grey balance; DE: Graubalance)
Gray balance is the combination of cyan, magenta and yellow tone values that prints as a neutral grey without a colour cast on a given process and substrate. Holding gray balance keeps neutrals and skin tones natural and is a sensitive indicator of whether the three process colours are in balance on press. It is the basis of G7 calibration and is checked on colour bars during a run.
Ink drawdown (drawdown)
An ink drawdown is a thin film of mixed ink spread on the actual substrate with a hand proofer or drawdown bar that approximates the press ink film, used to check a spot colour before printing. It shows how a Pantone colour will look on the real kraft, greaseproof or film rather than on white reference paper, and it is the best early check for spot colours. A signed drawdown is often kept as the colour reference for the production run.
See: Pantone vs CMYK in packaging
ISO 12647 (process control for halftone colour printing)
ISO 12647 is the series of international standards that sets process-control targets for halftone colour printing, such as solid colours in Lab, tone value increase and tolerances, with separate parts for different processes: part 2 offset, part 4 gravure, part 6 flexography, part 7 proofing and part 8 validation prints. It allows a buyer to specify CMYK work against a known printing condition rather than one Delta E per colour. ISO 15339 complements it with characterised reference printing conditions that are independent of the print process.
Measurement conditions (M0, M1, M2, M3)
Measurement conditions are the standardised illumination settings of colour-measuring instruments defined in ISO 13655: M0 is legacy, undefined UV content; M1 matches D50 including its UV component; M2 excludes UV; and M3 adds a polarising filter. Because many papers and boards contain optical brighteners that react to UV, readings of the same sample can differ between conditions. A colour specification should state which condition is used, together with the formula and tolerance.
See: Pantone vs CMYK in packaging
Metamerism
Metamerism is the effect in which two colours match under one light source but differ under another, because they reflect different spectra that happen to look alike under the first light. It is common when a colour is matched with a different ink set, substrate or process from the original. Viewing approvals in a light booth under more than one source, and knowing where the packaging will be seen, reduces surprises.
Pantone (Pantone Matching System, PMS)
The Pantone Matching System is the most widely used commercial spot colour reference in packaging, a numbered library of colours with mixing formulas published in printed guides. Each reference exists in coated (C) and uncoated (U) versions because the same ink looks different on glossy and absorbent stock, so the uncoated reference is the more realistic guide for kraft and uncoated papers. A Pantone number names a target; how closely it is reproduced depends on the substrate, process and agreed tolerance.
See: Pantone vs CMYK in packaging
Solid ink density (SID; DE: Volltondichte)
Solid ink density is the optical density of a 100 % ink patch, measured with a densitometer, used on press as a quick indicator of ink film thickness. Typical targets for sheet-fed offset on coated board lie roughly between 1.0 for yellow and 1.8 for black, depending on ink set, substrate and densitometer status, although current ISO 12647 editions define solids in Lab rather than density. Rising density increases colour strength but also dot gain, so it is controlled within a narrow window.
Spectrophotometer (DE: Spektralfotometer)
A spectrophotometer measures the full spectrum of light reflected from a sample and calculates colour values such as Lab, from which Delta E is derived. It is the instrument used to set and verify colour targets on proofs, drawdowns and printed samples, and modern press-side and inline versions also report density. Graphic arts instruments usually use 45°/0° geometry, and the measurement condition (M0 to M3) must be stated.
Spot colour (Pantone colour; DE: Sonderfarbe, Volltonfarbe; NL: steunkleur)
A spot colour is a pre-mixed ink printed in its own unit to reproduce one specific colour, usually specified from the Pantone Matching System. It gives cleaner, more consistent brand colours and flat areas than CMYK builds and reaches colours outside the CMYK gamut, but each spot colour adds an ink, a plate and a wash-up. In artwork, spot colours must be named exactly as agreed, because each name becomes a separate plate.
See: Pantone vs CMYK in packaging
Standard viewing conditions (D50, ISO 3664; light booth)
Standard viewing conditions are the controlled lighting and surroundings under which printed colour is judged, defined in ISO 3664 with D50 illumination of approximately 5000 K. Printers and brand owners use light booths built to this standard so that both sides of an approval see the same colour. Colours checked under shop LEDs or daylight at a window can look different, especially where metamerism is involved.
Prepress and artwork
What happens to artwork between the designer's file and the printing plate, and the artwork rules that come from it. File preparation is covered step by step in packaging artwork preparation.
Artwork (print-ready artwork)
Artwork is the graphic file that defines everything to be printed on a pack: text, images, colours, marks and codes, positioned on the dieline. Print-ready artwork is supplied at 1:1 scale, usually as a PDF/X file built on the manufacturer's dieline, with vector logos and text, images at sufficient resolution, named spot colours and bleed. Artwork that is not print-ready is a frequent cause of delay after an order is agreed.
See: packaging artwork preparation
Bar width reduction (BWR)
Bar width reduction is the deliberate thinning of the bars in a barcode file to compensate for ink spread on press, so that the printed bars reach their nominal width and the code scans and verifies correctly. The amount depends on the print process, plate and substrate and is set by the printer, typically larger for flexo on absorbent paper than for offset on coated board. On flexo, bars are often oriented in the direction of print travel to limit distortion.
See: packaging artwork preparation
Bleed (DE: Beschnittzugabe, Anschnitt; NL: afloop)
Bleed is artwork extended beyond the cut line so that small cutting variations do not leave unprinted edges. 3 mm is common for sheet-fed offset cartons and cups; flexo, corrugated and reel-fed bag work often needs 5 mm or more. The required bleed is set by the manufacturer for each product.
See: packaging artwork preparation
Choke and spread
Choke and spread are the two ways of creating a trap. A spread enlarges a lighter foreground object slightly into the darker background around it, while a choke expands a lighter background slightly into a darker object, effectively shrinking the object's knockout. The rule is that the lighter colour moves into the darker one, so the overlap is hardly visible; prepress software chooses the direction automatically, with manual correction for critical elements such as logos and small type.
Dieline (cutter guide; DE: Stanzkontur)
A dieline is the flat outline of a pack before it is cut and folded, showing cut, crease, glue and perforation lines. Artwork should be placed on the manufacturer's own dieline, kept on a separate non-printing layer set to overprint, because board thickness and machine settings change panel dimensions.
See: packaging artwork preparation; carton dielines, cutting dies and prototyping
Distortion compensation (arced and pre-distorted artwork)
Distortion compensation is the adjustment of artwork so that it looks correct on the finished product after forming, shrinking or wrapping, as opposed to plate distortion, which compensates for the press. Paper cups and cup sleeves are printed on fan-shaped blanks that become cones, so elements are placed along the arc and rotated to their local vertical; shrink sleeves need artwork pre-distorted for uneven shrinkage. The manufacturer's template for the exact size is the starting point.
See: paper cup printing; cup sleeve printing
Eye mark and registration marks (print mark, photocell mark)
An eye mark is a small solid printed block, usually in a dark colour on a light background, placed once per repeat so that a photocell on a bag machine, sealer or sheeter can cut or seal each item in register with the print. Registration marks, such as crosshairs, microdots and colour bars outside the trim, help the printer align colours and plates. Their position and size are agreed with the converter, and eye marks often sit in seams, gussets or areas later hidden.
Knockout (DE: Aussparen)
Knockout means removing the colours beneath a top object so that each ink prints on bare substrate, rather than one ink printing over another. It keeps colours true, because inks are largely transparent, but any misregistration between the object and its knockout leaves a visible gap unless a trap is added. Knockout is the default for most coloured elements in packaging artwork.
See: packaging artwork preparation
Overprint (DE: Überdrucken)
Overprint means printing a top colour directly over the colour below instead of knocking it out, so both inks mix where they overlap. Small black text normally overprints so it never shows a white gap through misregistration, and dielines, varnish layers and technical marks are set to overprint in the file. White objects and light colours must never be set to overprint, because they disappear or shift colour on press.
See: packaging artwork preparation
PDF/X (PDF/X-1a, PDF/X-4)
PDF/X is a family of PDF subsets standardised in the ISO 15930 series for reliable exchange of print-ready files. PDF/X-1a requires CMYK and spot colours only, embedded fonts and flattened transparency; PDF/X-4 allows live transparency, layers and ICC-based colour management. Both are common in packaging, and the printer specifies which version and output intent to use.
See: packaging artwork preparation
Preflight
Preflight is the automated and manual check of a supplied file before prepress work begins, testing items such as fonts, image resolution, colour spaces, spot colour names, bleed, overprint settings, minimum line weights and text sizes. A preflight report lists problems for the designer to correct before proofing. Preflighting catches common file errors early and avoids paying for plates made from faulty artwork.
Prepress (repro; DE: Druckvorstufe; NL: prepress, drukvoorbereiding)
Prepress, also called repro, covers all the work between receiving artwork and producing the image carriers: preflight, colour separation, trapping, distortion compensation, step-and-repeat, screening, proofing and making plates or cylinders. Packaging prepress adapts the same design differently for each process and substrate. Its cost appears on quotations as repro or origination charges, usually once per design.
Repeat length (print repeat; DE: Rapport)
Repeat length is the distance along the web after which the printed image repeats, equal to the circumference of the plate cylinder including plate and tape, or of the gravure cylinder. For bags, wraps and reels it must match the product length or a whole fraction of it, so the available repeats on a press partly decide which sizes can be printed economically. Repeat length and eye-mark position are stated in reel specifications for printed rolls.
See: printing on greaseproof paper
Rich black
Rich black is a black built from 100 % black ink plus percentages of cyan, magenta and yellow, giving a deeper black in large areas than black ink alone. It should not be used for small text, fine lines or barcodes, because any misregistration of the four colours creates coloured fringes. The total amount of ink in a rich black must stay within the total area coverage limit for the process.
RIP (raster image processor)
A RIP is the software that converts a print-ready PDF into the high-resolution, screened bitmap data used to image plates or cylinders, or to drive a digital press. It applies the screening method, screen ruling and angles, dot-gain compensation curves and, in flexo, distortion. Flexo plate imagers typically work at resolutions such as 2,400 to 5,080 dpi.
Safe zone (safety margin)
A safe zone is a margin inside cut and fold lines where text, logos and barcodes should not be placed, because cutting, folding and forming vary slightly. A safe zone of around 3 to 5 mm from cuts and folds is common, with larger margins on corrugated and around cup rims and seams.
See: packaging artwork preparation
Separations (colour separations; DE: Farbauszüge)
Separations are the individual image layers, one per ink, into which artwork is divided for printing: the four process colours, each spot colour, white underprint and varnish. Each separation becomes one plate, cylinder or screen. A separation preview or proof confirms the number of plates and which elements print in which ink, which is how buyers check that plate costs on a quotation match the design.
See: packaging artwork preparation
Step-and-repeat (ups; DE: Nutzen)
Step-and-repeat is the multiplication of a single design across and around the printing plate or sheet so that several items, called ups, print at once. The number of ups depends on the item size, press width and repeat length, and it strongly affects material yield and cost. Different sizes of the same design usually need separate step-and-repeat layouts and, on flexo, separate plates.
Total area coverage (TAC; total ink limit)
Total area coverage is the maximum sum of cyan, magenta, yellow and black tone values allowed at any point of an image, expressed as a percentage up to a theoretical 400 %. Each printing condition and colour profile defines its limit, for example around 300 to 330 % for common coated offset profiles and lower for uncoated papers and many flexo conditions. Exceeding it causes drying problems, set-off and loss of shadow detail.
Trapping (prepress trapping; DE: Überfüllung)
Trapping is a small deliberate overlap between adjacent colours that hides slight misregistration, the misalignment of colours on press. Trap widths depend on the print process and are generally larger for flexo and corrugated than for offset, typically fractions of a millimetre, and most packaging printers apply trapping in prepress because the right width depends on their press, plates and substrate. Not to be confused with ink trapping, the ability of one ink to accept another on press (see Ink trapping under Inks, drying and curing).
See: packaging artwork preparation
Varnish plate (varnish layer, varnish separation)
A varnish plate is the separation that defines where a print varnish or coating is applied, supplied in artwork as a separate spot colour layer set to overprint. It is used for spot varnish effects and, just as often, to leave varnish-free areas for glue flaps, codes printed later and heat-seal zones. The varnish layer should be named clearly, such as "Varnish" or "Varnish_free", so it is not mistaken for an ink.
White underlay (white underprint; US: white base)
A white underlay is an opaque white ink layer printed beneath colours so they stay bright on brown kraft, transparent or metallised film and some coloured boards. It is set up in artwork as a separate spot colour layer that becomes its own plate, usually slightly choked so it does not peek out at edges. On porous kraft a single white layer is rarely fully opaque, so the result is brighter but not identical to white stock.
Screening and halftones
How continuous tones become printable dots, and the limits each process places on gradients, highlights and image detail.
AM screening (amplitude-modulated screening; conventional screening)
AM screening reproduces tones with halftone dots at a fixed spacing, the screen ruling, whose size varies: small dots for light tones, large dots for dark ones. It is the conventional screening method for offset and flexo, predictable on press and well understood by plate makers. Its weaknesses are rosette patterns, possible moiré and the loss of the smallest highlight dots in flexo.
Dot gain (TVI, tone value increase; DE: Tonwertzunahme; NL: puntvergroting)
Dot gain, also called tone value increase (TVI), is the growth of halftone dots between the file and the printed result, so that a 50 % tone prints darker than 50 %. It comes partly from mechanical squeeze of ink under pressure and partly from optical effects as light scatters in the substrate, and it is higher on soft and absorbent papers such as uncoated kraft. Printers compensate with plate curves in the RIP, and standards such as ISO 12647 define target TVI values for each printing condition.
See: Pantone vs CMYK in packaging
FM screening (stochastic screening)
FM screening reproduces tones with very small dots of a fixed size, often in the range of about 20 to 35 micrometres, whose number and spacing vary with tone. It produces no rosettes or screen moiré and renders fine detail well, but it demands stable plate-making and press control, and on flexo the tiny dots are hard to hold on rough substrates. It is used mainly in offset and in highlight areas of flexo hybrid screening.
Halftone (DE: Raster)
A halftone is the reproduction of continuous-tone images, such as photographs and gradients, as patterns of dots that the eye blends into tones, because a printing press can only print ink or no ink at any point. The size, spacing and shape of the dots are set by the screening method and screen ruling. All CMYK images and tints of spot colours are printed as halftones.
Hybrid screening (XM screening)
Hybrid screening combines AM and FM methods in one image, typically using FM-style dots in the highlights and sometimes the shadows, where AM dots would be too small or fill in, and AM dots in the midtones. In flexo it lets gradients fade much further towards zero without the hard edge caused by the minimum printable dot. Plate makers apply it in the RIP; buyers see it as smoother vignettes.
Image resolution (ppi, dpi, lpi)
Image resolution describes detail at three different stages: ppi (pixels per inch) for images in the artwork file, dpi (dots per inch) for the imaging device or digital press, and lpi (lines per inch) for the halftone screen ruling. Images are typically supplied at about 300 ppi at final printed size, and bitmap line art at 1,200 ppi or as vectors. Confusing the three is a common cause of low-resolution artwork.
See: packaging artwork preparation
Minimum dot (highlight dot; bump curve)
The minimum dot is the smallest halftone dot a plate and press can hold and print consistently; below it, dots either disappear or print as a sudden step. In flexo the minimum dot is typically a few percent, depending on plate, screen ruling and substrate, which is why gradients that fade to zero can end with a hard edge. Prepress raises the lightest tones to a printable value with a bump curve, or uses hybrid screening.
See: packaging artwork preparation
Screen angle
Screen angle is the angle at which the rows of halftone dots of each colour are set, chosen so that the screens of different colours form a fine rosette rather than moiré. In offset, cyan, magenta and black are commonly set 30° apart, for example at 15°, 75° and 45°, with yellow, the least visible colour, at 0°. In flexo, angles are usually offset by 7.5° from these values to avoid interference with the 60° cell pattern of the anilox.
Screen ruling (screen frequency, LPI; DE: Rasterweite)
Screen ruling is the number of rows of halftone dots per inch (lpi) or per centimetre, and it sets the fineness of printed images. Indicative values are about 150 to 200 lpi for offset on coated board, roughly 100 to 150 lpi for flexo on paper, up to about 175 lpi or finer on film with HD plates, and about 40 to 100 lpi for flexo printed directly on corrugated. Higher rulings show more detail but need smoother substrates, finer aniloxes and tighter control.
See: flexo vs offset vs gravure vs digital printing
Vignette (gradient, fade; DE: Verlauf)
A vignette is a gradual transition from one tone or colour to another, or to the unprinted substrate. Vignettes print smoothly in offset and gravure but are a classic flexo challenge, because tones below the minimum printable dot break off with a visible edge, and long gradients can band. Designs for flexo often end gradients in a light tint rather than zero, or the printer adjusts the vignette in prepress.
Proofs and approval
The proof types used to approve packaging before and during production, and what each one can and cannot show. The complete approval workflow is in packaging artwork preparation, and sample and QC stages in packaging sampling and quality control.
Contract proof (colour proof; DE: farbverbindlicher Proof)
A contract proof is a colour-accurate print, usually made on a calibrated inkjet system to ISO 12647-7, that simulates a defined printing condition and serves as the agreed colour reference for CMYK work. It is verified by measuring a control strip such as the Fogra Media Wedge printed alongside the image. It is useful for CMYK on white board and less meaningful for spot colours on kraft or film, where a drawdown or printed sample is the better reference.
See: Pantone vs CMYK in packaging
Master sample (approved reference sample)
A master sample is a signed, approved printed sample of a design on the production substrate, kept by both buyer and printer as the reference for every following run. Recording the measured Lab values of brand colours on the master sample turns it into a numerical target that other plants and suppliers can match. Master samples fade and age, so they are stored dark and replaced periodically.
See: packaging sampling and quality control
PDF proof (digital proof)
A PDF proof is a digital file sent for approval of content and layout: text, positioning on the dieline, separations, barcodes and regulatory marks. It does not show accurate colour or material feel, and it is the stage at which spelling and legal text must be checked, because changes after plates are made cost money. Many printers send a separation view with the PDF proof so the buyer can confirm the number of inks.
See: packaging artwork preparation
Press approval (press check; DE: Druckfreigabe)
Press approval is the sign-off of colour and registration on the production press at the start of a run, either with the buyer present, remotely by photographs and measurements, or by the printer against agreed targets. It is the last chance to adjust colour, not artwork. Approved sheets or a length of reel become the reference for that run's quality checks.
See: packaging sampling and quality control
Soft proof
A soft proof is a colour-managed simulation of the printed result on a calibrated monitor, using the ICC profile of the target printing condition. It is fast and free and useful for checking layout and approximate colour, but screen viewing conditions and the monitor's own gamut limit its accuracy. It is not suitable for approving spot colours on kraft, film or other non-white substrates.
Wet proof (press proof; DE: Andruck)
A wet proof is a proof printed with real inks, plates and substrate, either on a dedicated proofing press or on the production press. It is the only proof that shows the true interaction of ink, substrate and process, including dot gain, opacity and gloss. Because it requires plates and press time, it is expensive and is usually reserved for new designs on critical substrates or where a contract proof cannot represent the result.
Registration and print defects
The names printers and quality teams use for print faults. Inspection methods and acceptance levels are covered in packaging sampling and quality control and in the testing, quality and defects glossary.
Banding
Banding is a pattern of visible stripes or bands in areas that should be uniform. In flexo it usually runs across the web and comes from mechanical causes such as gear marks, cylinder bounce or a damaged anilox; in inkjet it runs along the print direction and comes from blocked or misfiring nozzles. Long gradients and flat tints in mid-tones show banding most clearly.
Bridging (dot bridging, fill-in)
Bridging is the joining of adjacent halftone dots or fine elements by ink, so that shadows fill in, reversed text closes up and fine lines merge. In flexo a frequent cause is dot dipping, where dots smaller than the anilox cells dip into them and pick up excess ink, along with excess impression or low ink viscosity. It is controlled through anilox-to-screen ratio, impression and ink, and through minimum sizes in artwork.
Dirty print
Dirty print is flexo print with random spots, filled-in reverses and fuzzy detail caused by dried ink, paper dust or fibres building up on the plate. It worsens as a run progresses and is common on dusty uncoated papers and with fast-drying inks. Remedies include plate cleaning, ink drying-speed adjustment, web cleaning and appropriate impression.
Feathering
Feathering is ragged, hairy or irregular edges on printed elements, where ink spreads beyond the intended outline. It can result from excess impression, low ink viscosity, ink drying on the plate or ink wicking along fibres in absorbent papers. It degrades small type and fine lines and is most noticeable on uncoated kraft and tissue.
Ghosting (DE: Schablonieren)
Ghosting is a faint, unwanted repeat of an image element appearing elsewhere in the print. In offset it is usually mechanical: a large element depletes the ink on the form rollers, so the next pass of the same rollers prints a lighter shadow of that element in a solid area. It is reduced at design stage by avoiding solids directly in line with heavy elements, and on press by ink and roller settings.
Halo (haloing)
A halo is a dark outline around the edges of printed solids, type or dots, with a lighter centre, typical of flexo. It is caused by excess impression squeezing ink to the edges of the plate image. The same word is used for a light ring around a dot and for the coloured edge visible where trapping or misregistration leaves an outline, so it helps to agree which meaning is meant.
Hickey (DE: Butzen)
A hickey is a small spot of ink surrounded by an unprinted ring, or a white spot in a solid, caused by a particle of dried ink, paper dust or debris on the plate or blanket. Hickeys are mainly an offset defect and repeat in the same place on every sheet until the plate or blanket is cleaned. They are counted as cosmetic defects in print inspection.
Misregistration (out of register)
Misregistration is the misalignment of printed colours relative to each other, or of print relative to the cut, fold or seal positions. It shows as colour fringes, gaps between adjacent colours, blurred small multi-colour text or logos that sit off-centre on a panel. Small amounts are hidden by trapping; larger amounts come from web tension, film stretch, plate mounting or press mechanics, and print-to-cut register is controlled with eye marks on converting machines.
Missing dots (speckle, snowflaking)
Missing dots are areas where gravure cells fail to transfer ink, producing a speckled or snowflake appearance in tones and solids. They occur when a rough or incompressible substrate does not contact every cell, and are most visible in highlights. Electrostatic assist, smoother substrates and suitable impression rollers reduce them.
Moiré
Moiré is an unwanted interference pattern that appears when two regular patterns overlap at slightly different angles or frequencies, such as two halftone screens, a halftone screen and the anilox cell pattern, or a screen and a pattern in the image like fabric. It is prevented by correct screen angles, by choosing an anilox count that is a sufficient multiple of the screen ruling and by FM or hybrid screening for problem images.
Mottle (mottling; DE: Wolkigkeit)
Mottle is an uneven, blotchy or cloudy appearance in areas that should print as a smooth, uniform solid or tint. It comes from uneven ink absorption by the substrate, poor ink transfer or trapping, or press conditions, and is common on uncoated and recycled papers and on film without surface screening. It is judged visually and can be measured as variation in density across a solid.
Pinholing
Pinholing is the appearance of tiny unprinted dots in printed solids, where ink has failed to wet or cover the substrate. Causes include low surface energy on film, foam in water-based ink, too little ink volume, ink drying on the anilox or plate and substrate surface defects. Raising anilox volume, adjusting ink and treatment or using surface screening on the plate usually cure it.
Registration (in register; DE: Passer; NL: register)
Registration is the accurate alignment of each printed colour with the others and of the print with the product's cut, fold, seal or form positions. Register tolerances are process-dependent and are agreed in the specification, with CI flexo, gravure and offset holding tighter register than stack flexo on stretchy film. Designs with small multi-colour text or hairline-fit colours demand tighter register than bold, separated elements.
Slur (DE: Schmitz)
Slur is the smearing or elongation of dots and edges in the print direction, caused by slippage between plate or blanket and substrate, typically from excess impression, speed mismatch between cylinders or web tension problems. It makes halftones darker and edges blurred on the leading or trailing side. It is checked with slur targets in control strips.
Washboarding (fluting)
Washboarding is a striped pattern in corrugated post-print, where the ink prints more heavily on the flute tips under the liner and lighter between them, making the flute structure visible in solids and halftones. It is more pronounced with thin liners, coarse flutes and fine screens. Thicker liners, finer flutes, soft plates and coarser screens limit it, and pre-print or litho-lamination avoid it.
See: pizza box printing
Print varnishes
Clear coatings applied by a print unit or coater as part of printing. Foil stamping, cold foil and embossing are defined in the converting glossary, laminates in the materials glossary, and carton finishes are compared in carton finishes.
Aqueous coating (water-based coating; DE: Dispersionslack)
An aqueous coating is a water-based clear coating, usually acrylic, applied over print in gloss, satin or matt to seal the ink, speed up handling and resist scuffing in transit. It is applied inline from a coating unit on offset presses or from a flexo station and dries with hot air. It is distinct from an aqueous dispersion barrier, which is formulated for grease or water resistance rather than print protection.
See: carton finishes
Gloss, matt and satin varnish
Gloss, matt and satin describe the surface sheen of a varnish or coating: gloss reflects light directly and intensifies colours, matt diffuses it for a soft, low-reflection surface, and satin sits between them. Matt finishes mute colours slightly and can show scuff and burnish marks more readily than gloss. The chosen finish should be approved on a printed sample, because it changes how spot colours and images look.
See: carton finishes
Overprint varnish (OPV; DE: Drucklack)
An overprint varnish is a clear varnish printed over ink through a normal print unit, in offset traditionally an oil-based varnish that dries like the inks. It is low in cost and gives limited protection and gloss compared with aqueous or UV coatings. In flexo and gravure the term covers any clear varnish run from a print station, often water-based or UV.
See: carton finishes
Spot varnish (spot UV; DE: partielle Lackierung)
A spot varnish is a varnish applied only to selected areas of a design, defined by its own varnish plate, often a high-gloss UV varnish over a matt surround to highlight logos or images. It can be applied inline or offline by flexo, offset or screen printing, with screen giving the thickest, most tactile layer. It needs tight registration to the print, so very fine spot varnish details should be agreed with the printer.
See: carton finishes
UV varnish (DE: UV-Lack)
A UV varnish is a clear coating cured instantly by ultraviolet light, giving higher gloss, a harder surface and better rub and scuff resistance than oil-based or many aqueous coatings. For food packaging, residual photoinitiators and monomers can migrate, so a low-migration UV varnish processed under good manufacturing practice is needed. Heavy UV coatings can also affect folding and gluing, so glue areas are normally left varnish-free.
See: carton finishes
Varnish-free area (varnish knockout)
A varnish-free area is a part of the design deliberately left without varnish or coating, defined on the varnish plate. Glue flaps and seams need it so adhesive bonds to the board, and areas for later inkjet coding, date marking or heat sealing often need it too. Missing varnish-free areas are a common cause of carton gluing failures on the folder-gluer.
Turning print terms into a specification
A print specification that a printer can quote and hold to needs only a handful of these terms, stated clearly. For a packaging enquiry, the useful print lines are:
- Print process, if you have a preference, or the reason you need a particular one (for example fine type, photographic images, short run).
- Number of colours per side, split into process colours, named spot colours (Pantone C or U), white underlay and varnish.
- Colour targets: the reference (Pantone, Lab values or an approved master sample), the substrate it applies to, the tolerance and formula (ΔE00) and the measurement condition.
- Approval steps you need: PDF proof, contract proof, ink drawdown on the real substrate, printed sample or press approval.
- Ink requirements for food packaging, such as low-migration or mineral-oil-free systems and which side may be printed.
- Any print-to-converting requirements: repeat length, eye-mark position, varnish-free glue areas, barcode grade.
The packaging RFQ guide shows where these lines sit in a complete request, and the packaging cost drivers guide explains how colours, plates and coverage affect price. 9 Packaging is an Istanbul-based manufacturer and exporter of printed packaging for business customers, including fast-food and chain-style foodservice operations. If a printing term on a proof, specification or competing quotation is unclear, send it with your enquiry through our contact page and it will be clarified during technical review.