If you’re going to scrimshaw porous material you need to use a filling agent for the material you are working on, or a colorant that doesn’t penetrate much. Dipping the bone, or antler, in hot wax, and then driving it into the material with a heat gun works. You have to Scotchbrite the heck out of it afterwards, and fill the etching with unthinned artist acrylic paint, and then Scotchbrite it again. Sometimes just unthinned acrylic paint works without bleeding into the surrounding material. Every application is different.
Hungry Horse