What a finish separation is, and why the printer asks for one
When you order business cards with a spot UV logo, invitations with gold foil, or stickers on clear film with a white underlay, the press needs to know exactly where that extra layer goes. It cannot guess from a flattened picture of the finished design. A gold letter in your mock-up is just yellow-brown pixels to the machine. The printer needs a separate, precise map that says "foil here, nothing anywhere else".
That map is called a finish separation, a mask or a special layer, depending on who you ask. Getting it right is the single biggest factor in whether a special finish lands exactly on the artwork or sits half a millimetre to one side. This guide explains how to set up masks for the three special layers we see most often in online orders: spot UV, foil and white ink.
The ground rules that apply to every special layer
Different finishes have different quirks, but a handful of rules apply to all of them. If you follow only these, most files will pass the check first time.
- Solid, not shaded. A mask is either on or off. Use 100 percent of a single colour, usually 100 percent K or a named spot colour. Gradients, soft shadows and transparency cannot be translated into a layer of varnish or foil.
- Vector where possible. Logos and text in the mask should be live vector shapes or outlined type. A raster mask at low resolution gives jagged edges on the foil or UV.
- Exact position. The mask must sit in the same position, at the same size, on an artboard of the same dimensions as the colour artwork. Build it from a duplicate of the artwork file so nothing moves.
- Named clearly. A spot colour called "SpotUV", "Foil_Gold" or "White" tells prepress exactly what it is. A colour called "PANTONE 871 C" could be read as metallic ink to be printed, which is a different process.
Most online printers accept the mask in one of two ways: as a separate page in the same PDF (page 1 artwork front, page 2 front mask, and so on), or as a spot colour layer set to overprint inside the artwork file. Check the product page or ask before you build it, because each workflow is set up for one of them.
Spot UV masks
Spot UV is a clear, glossy coating applied only to selected areas, usually on top of matte or soft-touch lamination. It gives the contrast between shiny and dull that makes a logo catch the light.
What to put in the mask
Draw exactly the areas you want glossy in 100 percent K on a white background. Everything black gets UV, everything white stays matte. Common choices are the logo, a pattern across the background, or a photo on the front of a brochure cover.
Size and registration
Spot UV is applied in a separate pass, sometimes on a different machine, so it will not line up with the print to the hundredth of a millimetre. Plan for a tolerance of around half a millimetre. That means:
- Avoid UV on very fine lines and small text. Strokes under about 0.5 pt tend to break up or fill in, and small type can look blurry if the varnish is slightly off.
- If you want UV to match a logo exactly, some printers suggest making the mask very slightly smaller than the printed logo, so any shift stays inside the printed area.
- Keep UV at least 2 to 3 mm away from the trim and from fold lines unless it is meant to run off the edge. UV on a fold can crack.
For a wider comparison of coatings and when UV is worth it, see our article on finishing options when ordering print online.
Foil masks
Foil adds a metallic or coloured shine in gold, silver, rose gold, copper and other shades. It is applied either by hot foil stamping, which uses a metal die pressed with heat, or by digital foiling, where foil sticks to a toner or varnish layer printed in the shape of the design. Both need a mask, and both have limits on how fine the detail can be.
- Line thickness. Fine hairlines tend to break. As a rough guide, keep foil lines at 0.3 mm or thicker, and ask your printer for the exact minimum for their process.
- Small counters. The inside spaces of letters like "a", "e" and "o" can fill up with foil at small sizes. Serif fonts at small point sizes are the worst offenders.
- Large solid areas. Very large flat foil areas can show small flaws, bubbles or uneven adhesion. A pattern or outline often looks better than a big solid block.
- One mask per foil colour. Gold and silver on the same card need two separate masks, one for each foil, and each is a separate pass.
Decide what is under the foil. If a letter is to appear only in foil, knock it out of the printed artwork so the foil sits on plain paper or laminate. If you want foil on top of printed colour, leave the colour in place, but be aware that any slight shift will show a coloured edge next to the foil.
White ink layers
White ink is needed whenever you print on something that is not white: clear film for window stickers, kraft paper, coloured board, or metallic stock. CMYK inks are transparent, so without a white base underneath, colours on dark or clear material look weak or almost invisible.
How to build the white layer
- Create a spot colour and name it exactly as the printer asks, often "White" or "WHITE_INK".
- Draw white-layer shapes under every area where you want the colours to look solid and bright.
- Set that spot colour to overprint, so it does not knock out the colours on top. We have a whole article on overprint and flattening traps if that setting is new to you.
- Pull the white layer back slightly, often by about 0.1 to 0.2 mm, from the edges of the colour. This "choke" stops a thin white rim showing along the edges if there is any small misregistration.
If you want a design printed in white only, such as a white logo on a black card or a white outline on clear film, the white layer is the artwork itself. In that case, the CMYK part can be empty, and only the spot white prints.
Checking the file before you upload
Special layers are easy to break at the export stage. A good export can still flatten a spot colour into CMYK or drop an overprint setting. Before uploading:
- Export with a PDF/X preset, which keeps spot colours and overprint settings intact. Our guide to exporting a print-ready PDF goes through the settings.
- Open the PDF in Acrobat and use Output Preview to confirm your spot colours are listed by name and appear exactly where you expect.
- Turn on overprint preview and check that the white or UV layer is not punching holes in the artwork.
- Compare the mask page and artwork page at the same zoom level, switching quickly between them, to check alignment.
- Name the files clearly, for example "card-front-art.pdf" and "card-front-uv.pdf", if the printer wants them as separate files.
Ordering special finishes online with us
We print spot UV, foil and white ink jobs through our digital printing service, with file checks by a person, not only an automated upload check. When your artwork arrives, prepress confirms that each mask matches the artwork in size and position, that spot colours are named correctly and set to overprint where needed, and that lines and text in the mask are thick enough for the chosen process. If something will not print well, we tell you before production and suggest a fix, such as thickening a foil line or simplifying a UV pattern.
Not sure how to set up a mask in your software? Send us the artwork with a short note about which parts should be foil, UV or white, and we can advise, or build the separation for you for a small setup charge that we confirm in advance. Our general printing guides cover related file topics, and our team can be reached through the contact page.
A good test before you send anything: print the artwork page and the mask page on your office printer, hold them together against a window, and check that every black shape sits exactly where the finish should be.
