This works great, but be careful with gem stones. Some of them like amethyst and emerald and any others which are in the quartz family are heat sensitive. Just put them in once the water has cooled down some. Cubic Zirconia are fazed by anything. They are lab grown under high heat and pressure. I fire them in a kiln at 1650 degrees in silver metal clay jewelry, and they are bothered at all.
If the jewelry is very dirty or very tarnished – like silver or gold – then you may need to repeat the process so just add a little more baking soda and more boiling water – but make sure it’s boiling, that’s key! You can also use a toothbrush to get in all the nooks and crannies of detailed jewelry. Be careful with precious gems, stones and metals.