Don't know if it would work for what you're doing, but I have some cast iron bagpipers (2 1/2" tall) that I've had since boyhood (1950). Back then they painted a base color, like dark green, then made a few representative strokes over that to represent the tartan..in this case a yellow stroke, painted over with a thinner black stroke horizontally and a couple red strokes vertically. Gives the effect of a tartan.

Ron