Often a sizing / repair has to be done on jewelry which has gemstones set in it. A cabochon set in silver or gemstones set in gold can be protected in this manner when the repair is done.
Fill a stainless steel egg cup with coarse river or builders sand. Add water. Stand the ring in the sand with the gemstones facing down, protected by the sand and water. The soldering operation must be quick. The water will boil, which does not harm the gemstone. During the soldering operation caution must be taken that the water does not boil away.