Viscosity printing is a good way to print certain zinc or copper plates in multiple colors with only one run through the press. This innovative printing method was developed in the mid twentieth century by Stanley William Hayter. He experimented with applying layers of inks mixed with varying amounts of oil on a single plate. The differences in viscosity, or oiliness, kept the inks from mixing.
Here is my work station. I'm using etching inks in a variety of colors, and with a varying amount of added linseed oil. First, I wipe the zinc plate in the traditional way with the first color, which has no added linseed oil. Next, I roll out another color, which has a bit of added oil, and apply it over the first as a top roll. I do the same with the third color, which is oilier, or "looser" than the first two colors.
And here is my first print! It is exciting to see it, because there is some serendipity built into viscosity printing and you can't quite predict how it is going to turn out before you print.
By the end of the session, I'd printed seven different viscosity prints including ghost prints, ghost prints with newly added top rolled colors, and versions created by starting from scratch with fresh colors. I added stickies with notes to each, so I could recall procedures later.