Aloha Barbara! I've bought many OLD collections over the years & there isn't any easy answers. Basicly larger non-porcelan surfaced shells I put into the dishwasher. This works great w/Tritons & Helmets. Soaking in light clorox solution, say 20%, works well on most shells. Sometimes brushing w/soap & hot water helps if there's a oily film. A combination of cleaning methods works wonders. Last year I acquired a HUGE collection from the 1950's that must number in the thousands and after cleaning most of the World Record Sizes & other rarities I still have 90% to ponder over. I wish you luck. Mahalo! Chris Takahashi