Brownell's Acraglass dyed black works perfectly. You will need to find some polymer similar in construction to the frame material to fill the voids. Let the Acraglass dry about 24 hours, then shape with a file and finish with 600 grit wet sandpaper. Be very carfull when you build up the inside of the void so you don't get into a situation where you can't re-assemble the pistol. Easy to do if you're not carefull. PM me if you want to discuss the process.