6

I just read a good book on DTP.

The author stated that one should not overprint black text over metallic spot colours. Unfortunately he doesn't explain this further.

I would like to ask why not overprint black text over metallic spot colours, what is the problem?

  • 2
    This may relate to lithographic inks specifically. Most lithographic inks are transparent/semi transparent. So, if you print something black over a metallic ink, you will see it through the black ink. This could be undesirable. – Billy Kerr Apr 10 at 11:29
  • It would be the same thing if you were applying gold leaf, hologram, or other surface treatment that is incompatible with ink. – Harper - Reinstate Monica Apr 12 at 18:23
  • What book are you referring to? – chicks Apr 14 at 17:50
25

Transparent inks can't stick to the surface of metallic inks.

We've recently had this problem at the offset print house where I work. We wanted to print a black and white image where all the white areas were silver and for unknown reasons we forgot what we already knew.

First we simply printed a solid silver rectangle and printed the black image on top of it.

The result was that the black image became very faint. Almost not discernible. The ink simply didn't stick to the metallic surface of the silver spot color and it didn't look good at all.

The solution was to do the opposite: First print a solid black rectangle and then print the white areas in silver on top.

Since metallic spot colors are opaque the silver covered the black entirely and the black parts was only visible in the holes of the silver image.

It's advisable (if possible) to always print metallic colors on top of black ink (or some other ink, blue for example) since it gives the metallic color more depth than if it's printed directly on paper.

Please note, that the order in which the inks are applied has nothing to do with how you layer your objects in your document. It's a decision made by the printer. It's common to print metallic spot colors last. If you for some reason want to have influence on that, you need to talk to the print house.

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  • 2
    That is a devilishly clever solution. Storing that one in the long-term memory. – Vincent Apr 10 at 14:17
  • @Vincent, thanks. Working with metallic spot colors can be a little devilish compared to ordinary transparent inks because the order of the inks matters and you have to invert your intuition about how colors overprint. – Wolff Apr 10 at 14:23
  • Are there any combinations of transparent and metallic inks that would allow the former to be printed on the latter, so as to allow a variety of metallic colors to be produced by combining silver metallic plus other colors? – supercat Apr 12 at 19:42
  • @supercat, I can't say for sure, but I don't think so. You could of course print CMYK colors first and then print silver on top in some raster percentage or pattern to make some kind of "special effect", but I don't think it would look like multicolored metallic ink. There are a range of colored metallics available, but of course it would be expensive to print with several of those. And there are no color profiles for this, so you would have to freestyle. – Wolff Apr 12 at 19:51
3

My guess would be that either

  1. it complicates the printing process because it means that black ink will have to be applied after the spot ink (while default is spot inks are last) since the metallic ink is opaque;

    or

  2. a metallic spot ink is a bad surface to print on: the black ink may not stick to the metallic ink layer nearly as well as it does to the bare paper.

Possibly both factors play a role.

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3

CMYK ink is thinner and so gets sucked faster, sticks better to the paper without substantially altering the surface of the paper.

Spot ink however is more dense and forms a more elastic layer on top of the paper, think of it like kind of a 'rubber' coating, which is more tricky to print on, dries slower, etc.

In a more extreme comparison, think of painting with a brush, first on a piece of canvas, then, on a piece of glass — which surface sticks better? Where do you get a more predictable distribution of paint?

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