The foil backing found on some rhinestones has been noted to be able to be removed in a solution of salt (table or Kosher) and cider vinegar. The solution should be liquid enough to cover the stones. Allow them to soak for about three hours. Check on them as the process could go faster depending on the type of foil and process used to adhere it to the stones. Jewelry cleaner will often remove any remaining silver on the rhinestones.
The foil backing on Swarovski crystal is added in the manufacturing process. It is difficult to remove the backing deliberately. However, the foil will break down with the use of adhesives not suited for the foil back and the true color of the rhinestone will be compromised.
- Sandra Lupo, Jewelry Designer and Instructor and Swarovski crystal Ambassador