Recently I was making parts for a toy from BB plywood and decided I wanted to color them before finishing with a clear sealant. I decided to use some brightly colored alcohol-based ink for the job. The pieces had been scored with a design and by chance I began by applying a tiny bit of ink to an area that was bounded all around by a score line. The result surprised me.
The ink quickly wicked through the wood, but stopped right at the score line, making the bounded area brightly colored while leaving the wood outside the area completely untouched. Since then, I’ve used the technique quite successfully to make multicolored pieces with sharp boundaries between colors. Here’s a whistle, for example:
In addition to inking in the the star, I did the edges with brown ink. I made it that way so I could round over the cut edges with sandpaper (which exposes the light colored wood) and then make the rounded edges match the brown-colored cut edges.
The technique is pretty reliable, but not 100%, so it’s probably best used on parts that are small enough that you can tolerate the occasional failure of the ink to end up where it should… Most of the failures I’ve had are due to me being a klutz with a fine brush, but once in a while the ink does manage to escape, especially if I didn’t make the score line deep enough.