The manual for an ultrasonic cleaner says:

• “Cold, clean tap water is generally best suited as cleaning fluid. The cleaning effect can be enhanced by the addition of approximately 3 drops of washing-up liquid. Do not use caustic cleaners, ammonia, bleach or heavily perfumed detergents.” (emphasis mine)

I know a professional jeweler with decades experience who cleans jewelry (mostly gold) using “Mr. Clean”¹ and ammonia, diluted, in an ultrasonic tub. The cheap ultrasonic I bought for myself is not for pros - but jewelry cleaning is the advertised purpose and it has a stainless steel tub just like the pro models have.

So the question is, what’s the purpose of the ammonia avoidance guidance, and is the pro jeweler I know making a mistake by using ammonia?

UPDATE: I also have to question why the manual says to use cold water. Pro ultrasonics have built-in heating elements. The pro jeweler waits until the solution is hot before using it.

footnote:

① out of curiosity, is there a brand-neutral name for “Mr. Clean” (aka “Mr. Propre” in French regions)?