Letterpress ink is a funny animal. It’s thick and tacky, yet semi-transparent. Last week was the first time I ever printed on colored stock…can you believe that? I’ve been printing on white paper (white, cream, off white, ecru…50 shades of white, right?) for the past 2 years, so even though I always knew letterpress inks were transparent, I didn’t fully understand until printing on colored paper.
Transparent inks allow you to print 2 overlapping colors to yield a third color. Although registration could be difficult, this is a great way to get 3 colors for the price of 2. It’s simple, right? Imagine a venn diagram…a yellow circle on the left, a blue circle on the right, overlap them in the middle, and voila…green in the middle.
So this same principle holds true when printing on colored paper. I recently printed blue ink on yellow cover stock for some little booklets. When I mixed the blue according the the pantone formula guide, it turned out to be a near perfect match when printed on white lettra. BUT, look what happens when I tried that same blue on the yellow cover stock…hunter green. That made perfect sense…blue on top of yellow yields green. But how in the world can you print blue and still see blue on yellow paper?
Although I had warned the client the blue ink would look different on yellow stock, I was pretty sure they weren’t going to be happy with hunter green. So I decided to try a little experiment and swap out my transparent white mixing ink (ink with no pigment) with opaque white. I followed the pantone formula guide again and ran a test print on white stock just to make sure I was getting the right color. Although SLIGHTLY softer than the first blue, blue 2 (mixed with opaque white) was similar to blue 1 (mixed with transparent white).
It was time to try pulling a print on the yellow cover stock–SUCCESS! Let’s think about this for a second, why did this work? Conceptually, when I mixed blue 2 with opaque white, it allows a layer of white to mask out the yellow. Then when the blue is added, it lays on top of the white layer instead of the yellow paper. Even though I didn’t literally print white, then overprint in blue, it’s a similar concept. I’ve read and heard from veteran printers that opaque white yields pastel colors. This may be true, but it’s a GREAT way to print on colored paper.