We have steamed clams and want to save the clam shells to use for baked clams at a later date.Is there a way to clean the shells so they can be used. I don't like using the tin shells. 
Scrape the inside as clean as possible. Soap and water is probably sufficient if there is no muscle on the shell (plus you've already cooked them). If you want to be super careful you could steam, boil or pressure cook to be really safe, but I doubt it would be necessary.  I've even heard of folks putting them in the dishwasher to "sterilize." 