OK, an evaluation of the oil pencils method on rawhide.
Caveats:
1) All I had was a bend of cow rawhide, which is probably not going to be used to make drum with anyway, It's just too thick.
2) I just don't have the hand strength to stretch it transparency and smoothness.
So all in all, it's thick, rough, and about as rough as 120-180 grit sandpaper. Not exactly conducive to drawing smooth lines.
3) I also did not have my good ink pen, so I used a brush marker that was much to thick for the size of the example--the figure is only about 2 1/2 inches tall.
Pros:
1) Greasy spots? No problem. It accepted the pigments quite nicely, and the Testors smoothed the surface and blended the colors.
2) The Testors thinned the pigment to the point where it was absorbed into the hide.
3) The Testors evaporated away, leaving the pigment on the leather and dry.
Cons:
1) If you have a thick layor of pigment, it can rub into adjacent areas or bleed a bit with the Testors. See the hind legs and the far wing.
2) The rougher the hide, the coarser the details have to be.
3) The oils will need to be sealed in some way to prevent the oils from rubbing onto uncolored portions or to the beater (if used). A spray fixative meant for oil pencils would probably work. It tends to be non-crazing, flexible, and non-yellowing.
So all in all, it might be worth exploring, but I don't think it will be what you want to do. You need to find someone who has used alcohol-based inks, I think. The water-based might not work on greasy spots well?