How to Prepare Files for Letterpress: Plates, Impression and Ink

The short answer: letterpress prints from a raised plate made from your file, one plate for each ink, pressed into soft cotton so the ink sits at the bottom of a bite you can feel. Build every color as a 100% solid Pantone U spot swatch, in vector, with type outlined. Keep positive lines at 0.15 mm (0.4 pt) or heavier and positive type at 7 pt or larger; reversed lines and gaps at 0.3 mm, reversed type at 10 pt medium or bold. Keep any solid under 13 cm² (2 in²). No gradients, no tints, no light ink on dark paper.

Letterpress is a pressure process: it moves ink and it moves paper fibers, and a file that ignores either comes back at proof with filled-in counters, blotchy solids or the back ghosting through the front. For the craft background, start with what letterpress is. This guide is about the file.

How letterpress works: a raised plate pressed into soft paper

Letterpress prints from the raised surface of a plate, and on cotton it presses that surface into the sheet, so each line is inked and debossed in the same stroke. We make a photopolymer plate from your file: light hardens the polymer wherever your artwork is, the rest washes away, and your design is left standing in relief. On press, rollers ink only that raised surface. The plate meets the paper under pressure, and soft cotton gives way under the relief instead of resisting it.

That bite is why people choose letterpress; run a thumb across a good card and you feel the crevice of every line. It is also where every file rule comes from:

• Only solids print. A plate surface either touches the paper or it doesn't. There is no 40% on a plate, only a pattern of dots pretending to be 40%, and dots fill in.
• Ink spreads. Pressure squashes ink toward the edges of each stroke, so lines print a little wider than drawn and small gaps close. Positive and reversed elements need different minimums because of it.
• Paper moves. The impression displaces fibers down and out the back of the sheet. The paper, its caliper and whatever is printed on the other side all change how deep you can go.

One plate per color: every ink is a separate pass

Each ink color needs its own plate, its own hand-mixed ink and its own pass through the press, so a two-color card is two plates and two press runs, registered to each other. Between colors the press is washed up, the next Pantone is mixed, and the next plate is brought into register with what's already printed. Plate count, not object count, drives the setup.

The design consequence is simple: each color adds a plate and a pass. Front and back are separate plates, even in the same ink. The flip side is useful: once an ink is on press, everything in that ink prints in the same pass. A navy logo, a navy rule and a navy address are one plate, so reusing one ink across several elements costs nothing extra. Choose colors on purpose, and let one ink do as much work as it can. The same logic runs through all spot color work; see spot color and Pantone.

Solid spot colors only: no gradients, no tints, no CMYK

Build all letterpress artwork as 100% solid spot color. The plate can't print a 40% tint of blue; it can only print a field of raised dots that averages out to something paler, and on letterpress those dots behave badly. Each dot gains under pressure, small dots at the light end may not hold on the plate at all, and on textured cotton the whole screen reads coarse and uneven.

Our spec is plain: avoid halftones and gradients. If one is truly unavoidable, screen it at 85–100 lpi and keep every tint at 15% or above; anything lighter drops out. Photographs are a poor fit for the same reason. If a photo has to be on the piece, print it digitally or in offset on a separate operation and letterpress the type, or convert the image to true line art at 1200 ppi. Our guide to combining print finishes covers how those builds run.

• Want a lighter color? Mix it. A pale blue is a different Pantone and a separate plate, not a tint of the dark one.
• No CMYK builds, shadows, glows or transparency. A C100 M60 object has no plate to go to, and soft effects make tints. Assign every object to a named Pantone U swatch as a hard-edged solid.

Minimum line weight and type size for letterpress

Positive lines need 0.15 mm (0.4 pt) and positive type 7 pt; anything reversed out of ink needs 0.3 mm and 10 pt in a medium or bold weight. The difference is ink gain. The relief pushes ink outward at the edges of every stroke, so a positive line grows a little and stays crisp, while a reversed line is attacked from both sides at once.

Reversed type: bigger, heavier, more open

Reversed type is paper showing through ink, so every letter is a set of small gaps. At 10 pt medium or bold it holds; below that, the counters of a, e and g fill first, then thin strokes break up. Choose open counters and generous apertures, skip hairline serifs, add a little tracking. And since reversed type sits inside a solid, and solids have their own limit on cotton, use it as a small device: a monogram in a disc, a name on a narrow band.

Why letterpress holds finer lines than foil

Our letterpress positive minimum is 0.15 mm; foil's is 0.6 mm. Letterpress only has to carry ink on a narrow ridge of polymer; foil has to break a film cleanly along every edge of the die, and fine lines break or fleck. If one mark runs in both, build it to the foil rule; see foil artwork preparation.

Keep solids under 13 cm² (2 in²) on cotton

Any single solid ink area larger than 13 cm² (2 in²), about a 36 × 36 mm square, will mottle on cotton: the ink goes down uneven, with the texture of the sheet showing through in patches. Cotton is soft and irregular, and a flat plate can't push an even film of translucent ink into every hollow across a large area. Push harder to fill it and the plate bottoms out; the coverage gets splotchy anyway, and the fine type sharing that plate gets crushed.

If the design calls for a big field of color, there are three honest fixes:

• Let the paper be the color. Build a duplex card with a dyed ply for the field and letterpress the detail on the other side. The color is even because nothing was printed.
• Accept the texture. Some designers want the mottle. If that's you, say so in writing so we don't treat it as a fault at proof.
• Go blind. Press the shape without ink and let shadow do the work. See blind letterpress below.

For an opaque or metallic field, foil is the other route; it goes down as a film, not an ink, so it doesn't mottle the same way.

Impression depth: 0.2–0.6 mm, and what controls it

We run letterpress impression between 0.2 and 0.6 mm deep, and where a job lands in that range is set by the paper, the artwork and the back of the sheet, not by a number in your file. You don't draw depth. You choose the conditions that allow it.

• The paper. Soft, thick cotton takes the deepest bite; harder, smoother sheets take a shallower, crisper one. See best papers for letterpress.
• Printing area on the plate. Press force spreads across every raised surface, so the same force bites shallower on a large solid than on fine type. A plate mixing both is set as a compromise.
• The other side. A deep bite pushes through a single sheet, and a printed back fights it. That's the next section.
• Shadow. Deep impression casts a shadow line along each stroke, so small type reads heavier than on screen.

Printing both sides: why deep impression needs duplex

If both sides of a card carry letterpress with real depth, use 32 pt (0.8 mm) duplex or heavier. On a single sheet, each side's impression pushes through to the other: the front bite raises a bruise on the back, the back bite raises a bump on the front, and where the two overlap each one pushes the other back out, so both print shallow and uneven.

Duplex solves it mechanically. Each ply is printed on its own, backed by a flat platen, so it takes a full-depth bite; then the plies are mounted and the bruises face each other inside the glue line. The plies don't have to match, so the back can be a different paper color. On a single sheet, keep the back to a light impression, away from the deep areas of the front.

Where colors meet: trap, gap and registration

Separate letterpress plates register to each other within ±0.3 mm, so colors that touch need a 0.3 mm trap and colors that don't touch need at least 1 mm of paper between them. Registration is mechanical: the sheet goes through once per color, and each pass can sit a fraction of a millimeter off the last. A butt join, where two colors meet exactly edge to edge, opens a line of bare paper as soon as they drift (see the bottom row of Fig. 2).

Ink is translucent: dark paper, white ink and paper color

Letterpress ink is translucent, so it can only darken the sheet it lands on. Light ink on dark stock is not offered: it reads chalky and uneven, or disappears. White ink on uncoated cotton is not offered for the same reason. For light-on-dark, use foil, which goes down as an opaque film; for white, the term to ask for is white pigment foil. For tone-on-tone, a blind deboss.

Translucency also means the paper tints every ink. Blue ink on cream stock shifts greener; any ink on ivory reads warmer than on bright white. Always pick colors from the Pantone Uncoated (U) guide for cotton, and judge them against a real sample of the paper, not a screen. Our guide to spot color and Pantone goes deeper, and the paper library and sample pack show the actual shades.

Blind letterpress vs deboss

Blind letterpress is a letterpress plate run with no ink; a deboss is pressed with a metal die. Blind letterpress gives the same soft, pillowed edge as inked letterpress. A deboss die presses deeper, 0.3–1.0 mm, with crisper walls, and can carry foil in the same strike. Either way, blind is its own plate or die and its own pass: one plate can't print ink in some places and none in others.

A blind impression reads by shadow alone, so detail that holds in ink can vanish blind. Build blind elements to the deboss rules: 0.5 mm strokes, 1 mm gaps, 10 pt type. Put the art on its own layer in a spot swatch named DEBOSS and write “blind letterpress” in your order notes. More in embossing vs debossing.

Letterpress with foil: knock out, never stack

Foil lands on bare stock only, so knock the letterpress ink out wherever foil goes and leave a deliberate 1 mm gap between foil and ink rather than butting them. Foil doesn't bond reliably over an ink film, and it registers to print at ±0.5 mm, so a butt join shows either a sliver of paper or foil sitting on ink. Put the foil art on its own layer in a swatch named for the foil, such as FOIL-GOLD, set to overprint. The full rules for mixing processes are in combining print finishes.

How to build a letterpress file

Run this list before you export. It is the same list our prepress team checks against; the general version for every process is in how to build a print-ready file.

• Artboard at trim size, 3 mm (0.125 in) bleed on anything that touches the edge, 3 mm safety margin for all copy.
• Every ink is a named Pantone U spot swatch at 100%, for example PANTONE 2955 U. No CMYK, RGB or Lab objects anywhere.
• One swatch per ink, no duplicates: PANTONE 2955 U and PANTONE 2955 C in one file are two plates.
• All artwork vector. Type outlined, or fully embedded.
• Any raster line art is a 1-bit bitmap at 1200 ppi, colored with the spot swatch.
• No tints, gradients, transparency, shadows or glows. Halftones only if agreed: 85–100 lpi, nothing under 15%.
• Positive lines at least 0.15 mm (0.4 pt), positive type at least 7 pt.
• Reversed lines and gaps at least 0.3 mm, reversed type at least 10 pt medium or bold.
• No single solid over 13 cm² (2 in²), unless you've chosen the texture and said so.
• Touching colors trapped 0.3 mm; separate colors at least 1 mm apart.
• Foil, blind and cut art each on its own layer in its reserved swatch (FOIL-GOLD, DEBOSS, CUT), set to overprint; ink knocked out under foil.
• Right-reading art. Don't mirror anything; we make the plates.
• Exported as PDF/X-4, which keeps spot channels and layers. PDF/X-1a and native AI are accepted.

Separations, overprint and trap directionAGENCY LEVEL

Swatch names become plate names

Each spot swatch in the PDF becomes a separation, and each separation becomes a plate. Use the exact name from the current Pantone Uncoated library, and check the output in Separations Preview (Acrobat Output Preview or InDesign) before you export: you should see your Pantone plates and nothing else, with the CMYK plates empty. Stray swatches from placed logos are the usual culprit; merge them into the right ink.

Overprint: when it helps and when it lies

By default, spot inks knock out of each other: where black sits on blue, the blue is removed underneath. Keep it that way. Letterpress inks are translucent, so an overprint doesn't cover, it mixes; overprint only when you want the third color the overlap makes, and tell us. Finish layers (FOIL-GOLD, DEBOSS, CUT) are set to overprint so they don't punch holes in the ink artwork. The flip side: an overprinting foil layer won't knock the ink out for you. Cut the ink away under the foil in the ink artwork itself, with the 1 mm gap built in.

Trap direction: the lighter color spreads

Where two inks touch, spread the lighter color 0.3 mm under the darker one. The darker ink defines the visible edge, so the shape the eye reads doesn't change, and the overlap disappears under it. The quick way: give the lighter shape a 0.6 mm stroke in its own color, centered on the path and set to overprint. Half the stroke, 0.3 mm, falls outside the shape and under the neighbor. Where both inks are close in value, spread the one whose outline matters less.

Kiss vs deep impression, and the caliper it needs

Counting plates and passes

Tolerance stack-up near the trim

Letterpress registers color to color at ±0.3 mm, foil to print at ±0.5 mm, and the stack is cut at ±0.8 mm. The largest is the cut. A thin border 3 mm inside the trim reads a visibly different width from card to card because the knife moved, not the press. Keep borders well inside or bleed them off. How proofing works explains what we check at proof.