Foil and spot UV: how to prepare the mask file

Foil and spot UV are finishing touches that catch the light and make a cover feel special in the hand. The press cannot guess where you want them, so you tell it with a second file called a mask. A clean mask is simple to make once you know the few rules it has to follow.

What foil and spot UV are

Foil is a thin metallic or colored film pressed onto the cover with heat. It is most often used for titles, author names and small ornaments, and it shines in a way printed ink cannot.

Spot UV is a clear, glossy coating applied only to certain areas of the cover. It adds shine and a slightly raised feel to the parts you choose, such as the title or one element of the illustration, while the rest of the cover keeps its own finish.

Both look best against a calm background. Spot UV is most striking over matte or soft touch lamination, where the contrast between dull and shiny is strongest. We do not offer spot UV over gloss lamination, because a shiny coating on an already shiny cover barely shows.

What a mask file is

A mask is a black and white map of your cover. It tells the printer exactly where the effect goes and where it does not.

• Same size as your cover file. The mask has the same dimensions as your cover, including bleed, spine and any wrap area. It lines up with the cover like a sheet of tracing paper.
• Solid black where the effect goes. Use 100 percent black, with no tints or shades of gray.
• White everywhere else. Anything that is not solid black gets no foil or spot UV.

Each effect needs its own mask. If you want foil on the title and spot UV on an illustration, that is two separate mask files, plus your cover.

How to make one

The easiest way is to build the mask from the cover itself, so everything lines up.

1. Open your finished cover file and save a copy.
2. Delete or hide everything except the elements that will get the effect.
3. Turn those elements solid black, and make the background pure white.
4. Export at exactly the same size and settings as your cover.

In InDesign, Affinity or Illustrator, the cleanest method is to keep the effect on its own layer in your cover document. Export the cover with that layer hidden, then export the mask with only that layer showing, colored black. If you use the same document for both, the positions cannot drift.

Use vector shapes and live text where you can. Edges stay crisp at any size. If the mask has to be an image, export it at 300 DPI or higher so curves do not turn jagged.

Common mistakes to avoid

• Gray or soft edges. Feathered edges, drop shadows and anti-aliased blur are not solid black, so the printer has to guess. Keep edges hard.
• Gradients. Foil and spot UV are either on or off. A fade from black to white cannot print as a fade.
• Lines that are too fine. Very thin strokes and tiny type can fill in or break up. Minimum sizes vary by printer and by effect, so check your template and keep details on the bold side.
• A mask that does not match the cover. If you move the title on your cover after making the mask, make the mask again. A mask built for an older version will land in the wrong place.
• Effects too close to a fold or trim. Treat foil and spot UV like text: keep them inside the safe area, at least 0.25 inch from the trim, and away from the spine folds. Your printer may ask for more room, and we will tell you if so. The bleed, trim and safe area guide explains why.

Expect a little variation

Foil and spot UV are applied in a separate step after printing, and the alignment between that step and the printed ink can shift very slightly. Designs that place foil exactly on top of a thin printed outline are the hardest to get perfect. Designs that let the effect stand on its own, or overlap the printed art a little, are much more forgiving.

A digital proof shows where the effect is placed, but it cannot show the shine itself. If the finish matters a lot to you, a sample pack lets you see and feel foil, spot UV and the laminations in person before you choose.

Ready to add a finish

Choose foil or spot UV in your specs, then download the free cover template from the spec picker. It is built for your exact book, so your mask will be the right size from the start. When you upload, the mask goes in its own slot next to the cover, and our file check compares their sizes and flags anything that does not match. If you would rather not build the mask yourself, we can help prepare your files.