You have to be very careful as it's an extremely brittle material if thin. It sands down quite well using 180 then 240 grit wet n'dry abrasive paper. For cutting, I've found that its better to clamp it to a thin piece of substrate, e.g. thin ply and cut both carefully at once using a very fine fretsaw or Dremel cutter.

I was given a sizeable but thin piece by a local luthier I know well recently (having sold to enthusiasts the thirty or so genuine tortoiseshell picks I had left over from my music shop days aeons ago) and must take the plunge to fashion this into a mandola pickguard!

For anyone interested, use only old or antique tortoiseshell as it's now a protected species due to over-exploitating in former times and trade is banned.

Peace

moo