How do you clean antique tortoise shell?

Apparently you should coat the underside of the whole shell with polyurethane (forgive if the spelling is not correct) boat resin-this will appaernetly stabilise the shell esp. if brittle and killbacteria, then with a cloth polish the topside lightly with jewellers rouge , then coat the top with a fibreglass resin like the first available from a boat shop -you would be best to discuss it with them in case their are better options re-the resin. I myself am starting this today with three shells, good luck.