I have used a heated ultrasonic and Joy liquid detergent, for years.
The unheated ones I tried did not work well. Joy because it smells
better than ammonia and I was told it would not leave a film. The
heated ultrasonic is very effective for removing buffing compounds.
At one time I estimated it ran at 140 degrees F, a little too hot to
put my hand in. I leave it on all the time to maintain temperature.
The top stays on so the water will not evaporate below the level of
the heating elements. Mine is Otto Frei's house brand, the smallest
The ultrasonic can frost a sterling surface. But if you can hang
your piece in the hot solution to soak for awhile, you can then
clean it with a short burst. I never trust it with fragile stones,
like emeralds and opals.
I hope this helps.