I have worked on several and I used acrylics for the painting. I also used a dremel tool to remove the outer layer of the surface which leaves an ivory coloured under side exposed. If you want to paint on the outside of the antlers, you could paint directly on the outside after a quick wash to make sure they are clean. If you remove the outer layer (which is quite hard) you may have trouble getting it smooth or level to paint on. I have also used the dremel to shape the forms of the paintings before painting them. If you have any other concerns, I’ll keep an eye on your thread.
The one post that I did is in the “sculpture” forum on page six near the bottom of the page if you want to see an example. The birds are all painted with acrylics and no problem with the application or the texture.