Paper Coatings & Surfaces · The Complete Guide

Paper coating is a layer of mineral pigment and binder applied to the paper surface during or after the papermaking process. It fills the micro-roughness of the raw paper surface, the gaps between individual fibres, with a smooth, uniform mineral layer. The result is a surface that is fundamentally different from the raw paper in every property that matters to printing: smoothness, whiteness, ink holdout, dot reproduction, and light reflectance.

The difference between coated and uncoated paper is one of the largest single quality variables in printing. The same design, printed on the same press with the same inks, will look noticeably different on a coated versus uncoated surface. Colours are more saturated, dots are sharper, and the image has more apparent depth on coated paper, because the coating prevents ink from being absorbed into the fibres and keeps it on the surface where the light can interact with the pigment fully.

The coating formulation

Paper coating is a mixture of three main components applied as an aqueous slurry:

• Mineral pigments, kaolin clay (for smoothness and ink holdout) and calcium carbonate (for brightness and opacity). The ratio of kaolin to calcium carbonate determines the surface character: more kaolin gives a smoother, more ink-receptive surface; more calcium carbonate gives higher brightness. Cast coated papers use clay almost exclusively for maximum smoothness.
• Binders, typically styrene-butadiene latex or starch-based systems. The binder holds the pigment particles together and adheres the coating to the paper. The binder content determines the coating's strength, flexibility, and ink absorption rate. Too little binder and the coating is weak and dusts; too much binder reduces ink holdout and gloss.
• Additives, optical brightening agents (OBAs or FWAs, fluorescent whitening agents) that absorb UV light and re-emit it as blue-white visible light, increasing apparent brightness. Also includes lubricants, cross-linkers, and viscosity modifiers.

Application methods

• Blade coating (knife coating), the most common method for commercial coated papers. A steel blade meters the coating to a precise thickness as the paper passes beneath it. Produces a smooth, uniform coating that follows the surface contour rather than levelling it. Result: very smooth, uniform surface. Standard for coated art papers.
• Air knife coating, a high-velocity air blade removes excess coating after application. Produces a more textured surface than blade coating. Used for some specialty papers and certain packaging boards.
• Cast coating, the coated paper is pressed against a highly polished, heated chrome drum while the coating is still wet. The coating dries in contact with the mirror surface, adopting its smoothness perfectly. Produces the highest-gloss surface available, essentially a mirror finish. Energy-intensive and slow, hence the premium cost of cast coated papers.

Calendering · the final surface quality step

After coating, most coated papers pass through a calendering operation, a stack of hard steel or soft elastic rollers that compress and smooth the coating surface under high pressure. Heavier calendering produces higher gloss. Lighter calendering (or no calendering) produces matte or silk surfaces. The calendering conditions set the final gloss level of the paper.

• Supercalender (SC), produces very high gloss on mechanical papers
• Machine glazed (MG), one side dried against a polished cylinder, one side against felt, C1S papers for labels and wrapping
• Soft nip calendering, produces silk/satin surfaces with intermediate gloss
• No calendering (mat-formed), produces very low gloss matte surfaces

Gloss coated art · the commercial standard

Gloss coated art paper (also called art paper or art coated) is the most widely used commercial printing paper in India. The calendering process compresses the coating to a smooth, reflective surface. Gloss level: 60–85 GU at 60° geometry.

• Produces the richest colour saturation, the glossy surface reflects light uniformly, and the ink sitting on the surface has full contact with the light for maximum visual impact
• Sharpest halftone dot reproduction, the smooth surface holds dot edges precisely. Fine screen work (175 LPI+) performs best on gloss coated
• Some readability disadvantage on text-heavy pages, reflections from overhead lighting can make extended reading less comfortable. Not ideal for text-heavy publications under direct artificial light.
• Standard for product catalogues, brochures with strong imagery, packaging with colour photography, and magazines

Matte coated art · the professional standard

Matte coated paper has the same mineral coating as gloss but with matting agents (fine silica particles) in the top coat that scatter light rather than reflecting it uniformly. Gloss level: 8–20 GU. The surface is smooth to the touch, it is not rough or textured, but it does not reflect light like gloss.

• Excellent readability, no glare, no reflections. The standard for publications with significant body text: annual reports, corporate documents, books, training manuals.
• Colours appear approximately 10–15% less saturated than on gloss coated, the scattered light gives a softer, more subdued colour rendering. This is the trade-off for readability.
• The highest-quality combination in print finishing: matte lamination + spot UV. The matte base provides the flat, professional background; the spot UV creates high-contrast gloss accents on selected elements.
• Fingerprints are less visible on matte than gloss, matte paper is more forgiving of handling marks

Silk / satin coated

A middle ground between gloss and matte, produced by soft-nip calendering that smooths the coating less aggressively than gloss calendering but more than matte. Gloss level: 25–45 GU. The surface has a soft sheen that reads as elegant without the full reflectivity of gloss.

• Better colour saturation than matte with better readability than gloss, the practical choice for many premium brochures and corporate communications
• Increasingly common in premium packaging where gloss feels too commercial and matte too flat, silk provides a midpoint that communicates quality without either extreme
• Takes lamination, spot UV, and embossing well, compatible with all standard finishing processes

Cast coated · the highest gloss available

Cast coated paper has the highest gloss level of any commercially available paper, 85–100 GU at 60°. Produced by drying the wet coating against a polished chrome drum, the coating surface replicates the drum's mirror finish exactly. The result is a surface indistinguishable from a glossy photograph.

• Used for premium labels (product and wine labels), premium business card stock, packaging inserts, and any application where the maximum possible gloss is the design intent
• More expensive than standard gloss coated art, the slow, energy-intensive production process commands a significant premium
• Excellent ink density, the very smooth, sealed surface keeps ink entirely on the surface, producing the maximum possible colour density from a given ink weight
• More sensitive to scratching and marking than standard coated art, the mirror surface shows any contact marks. Apply a protective varnish or lamination for applications involving handling.
• Available in C1S (one side cast coated, one side uncoated) for label applications where the back is adhesive-coated

Uncoated paper

No mineral coating, the print surface is the paper fibre itself. The surface absorbs ink into the fibre structure rather than holding it on the surface. This produces a softer, more natural appearance that coated paper cannot replicate.

• Lower ink density and more dot gain than coated paper, the ink spreads slightly as it is absorbed. This requires adjustment to plate curves and ink quantities when switching from coated to uncoated printing.
• Warm, tactile quality, uncoated paper communicates a different set of brand values from coated. Heritage brands, sustainability narratives, premium stationery, and craft market positioning often favour uncoated.
• Can be written on, essential for letterheads, forms, notepads, and any paper that will receive handwriting or inkjet/laser overprinting
• Requires higher ink coverage to achieve equivalent visual density to coated paper. Ink costs are higher per unit for equivalent visual result.
• Available in a wide range of textures: smooth wove, laid, felt, linen, and various embossed textures. The texture itself is part of the design communication.

C1S means Coated One Side, the paper or board has a mineral coating on the print (front) side only. The back is uncoated. C2S means Coated Two Sides, both faces have a mineral coating. The choice between C1S and C2S depends on whether the reverse face is printed, visible, or must accept adhesive or lamination.

Ink holdout is the ability of a paper surface to retain the printed ink on the surface rather than absorbing it into the substrate. High ink holdout means the ink stays on the surface, it dries by oxidative polymerisation on top of the coating, retaining its full pigment concentration and producing maximum colour density. Low ink holdout means the ink vehicle is absorbed into the paper fibres, leaving behind a depleted pigment layer with lower density and a chalky, flat appearance.

How different surfaces affect ink holdout

• Cast coated, maximum ink holdout. The very smooth, sealed surface prevents virtually all ink vehicle absorption. Colours at maximum achievable density. Risk: ink takes longer to dry, oxidative drying is slower when the vehicle cannot absorb into the substrate at all.
• Gloss coated art, very high ink holdout. Small amount of ink vehicle absorbed into coating pores during impression. Produces excellent density with reliable drying speed. The standard for most commercial colour work.
• Matte coated, good ink holdout, slightly lower than gloss. The matting agents (silica) in the coating create more micro-porosity than gloss coatings, allowing slightly more vehicle absorption. Colours appear approximately 10–15% less dense than on gloss at same ink weight.
• Silk / satin, between gloss and matte ink holdout. Intermediate density and drying speed.
• Uncoated offset, low ink holdout. Significant vehicle absorption, ink density is limited by the amount of vehicle that remains on the surface. Dot gain is 30–40% versus 10–20% on coated papers. Total ink coverage must be reduced to avoid show-through and drying problems.

Ink holdout and drying speed

There is a direct relationship between ink holdout and drying speed. The more the ink vehicle is absorbed into the substrate, the faster the remaining oil in the ink oxidises and sets. High-holdout surfaces (cast coated, gloss) hold more vehicle on the surface, they take longer to dry. Low-holdout surfaces (uncoated) absorb the vehicle rapidly, they dry faster but at lower density.

In practice this means: jobs on cast coated or high-gloss papers require longer inter-unit drying times on press, more IR dryer output, higher anti-setoff powder quantities, and lower pile heights. Jobs on uncoated paper dry faster and can be handled sooner after printing.

The surface of the paper or board is the foundation that all finishing operations work on. Lamination, UV varnish, foil stamping, and embossing all interact differently with different surfaces. Getting the surface right before specifying the finish prevents costly failures in production.

These are typical values, actual measurements vary by specific paper brand, mill, and production batch. For critical colour-managed work, always characterise the specific paper with a printed characterisation chart and build an ICC profile or plate curve from the actual measured values, not from nominal specification values.