Is a soft, worn toothbrush a good tool for cleaning gemstones?
Cleaning gemstones is not rocket science. First and foremost DO NOT use a sonic cleaner and you will pretty much be safe. I always use a gentile soap, a soft brush and warm water. Opals and Turquoise I just use water, soft brush and warm water. Water is the best solvent in the world and a goo soaking will loosen most any gunk. I have never had any problems with jasper, Opal, pearls, Turquoise, coral, sapphires and emeralds. These are the stones that I am most familiar with. I have been cutting these since I was young, we will not mention how many years, I learned how to cab these in high school and how to clean them then. I have tried other methods and I have screwed up a few softer stones along the way. I do own a sonic cleaner but I use it for watch parts and for cleaning up castings only. Nothing worse in the world than checking in on your sonic cleaner and finding a stone has crumbled to a thousand pieces or it goes in one color and comes out all together something different.
All the best.