Hi Tom,
You can burnish the handle with almost anything smooth. First start out by sanding the handle until all the washers are even and you have the contour you want. Do the sanding while the leather is dry. A drum sander mounted in a drill press will work well to do most of the work, then sand by hand to finish it off. 100 grit for the shaping and 150 for finishing it off.
When you are ready to burnish it, wet the leather with a sponge just enough to get the outside damp. Then take whatever you have to burnish with and rub like crazy with a fair amount of pressure. As the leather burnishes it will begin to get slick and darken in color. You know you are doing a good job when you hear the leather start o squeak a little. Continue rubbing a little after you hear the squeaks.
A smooth wooden dowel or piece of hardwood like maple or ash are good for burnishing. Cocobolo wood makes the best burnishers. Smooth plastic will work too. Another good way is to rub a little glycerin saddle soap on a piece of canvas and rub with that. Just be careful because it tends to get hot and your fingers tips will get burnt.
A dowel mounted in the drill press spinning around 800 rpm can make the burnishing go a lot faster.
Here's a pic of the burnisher I had made from Cocobolo wood.
