The handles are made by casting acrylic resin with wood. The colors come in when you dye the wood and also when you mix colored inks in the acrylic. This is another art form by itself.
I needed a pressure pot for casting acrylics and a vacuum pot to stabilize the wood. I didn't make the ones on these knives. I bought blocks that people had cast for making duck calls and shaving brushes. I cut them up on my bandsaw to the size I need. The ones on the fillet knife came from the Ukraine!
I'm all set up to make my own now!