Safely Tumbling Freshwater Pearls and Silver?
(Toronto, ON, Canada)
As pearls are soft, it's the banging around in there and the abrasiveness of the shot or other hard items in the tumbler that will damage them.
You can wash pearls with a gentle unscented soap and water mixture, taking care to rinse thoroughly. This is a good idea to do occasionally to remove perfume, oils, etc. that can rot (for lack of a better word) the strings from the inside of the pearl out. If the pearls are strung on silk or another natural fiber string, lay them out flat to dry to avoid drying kinks in the string.
I would not tumble pearls in any medium as to not scratch/damage the nacre. You can "lift off" tarnish by using a solution of 2 tablespoons baking soda and 1 teaspoon salt in a shallow dish lined with aluminum foil. Pour boiling water over the solution to dissolve. While the water is still very hot - not boiling, place the silver item in in the foil-lined dish. Let soak. Within a few minutes to half an hour the tarnish will be dissolved.
Be sure to warm up your pearls by immersing them in increasingly hot water as from your tap before putting them into the very hot solution. Boiling pearls in NOT a good idea! :)
NOTE: This method will remove ALL the tarnish, including antiquing. It also removes silver plate, so be sure you are putting solid silver items into it.
This is a simple reaction between the aluminum metal and the silver sulfide (tarnish). The salt acts as an electrolyte allowing the reaction to happen.