For what it's worth, I've done this with baking soda (bicarb)
and a little dish detergent, and it worked fine, though I was
cleaning just silver, no pearls. --Noel
As I understand it, the bicarb or carbonate is there mostly to make
the water electrically conductive. the contact between the silver
and the base metal creates an electrolytic potential, which is what
then reduces the sulphides, cleaning the tarnish off of the silver.
I could be wrong, but near as I can see, about the only difference
between them is that sodium carbonate, being more alkaline, would
provide a bit more wetting power and some cleaning power to get
through any oil or grease, and it might allow greater soluablity of
the sulphide ions, but in that, I’m just guessing a bit… For
that matter, I’d bet, though I’ve not tried it, that a number of
other chemicals would also work as the powder added to the water.
TSP, for example, comes to mind, since it’s what I use to mix up the
electrolyte in anodizing titanium or niobium. It’s
detergent/cleaning power is useful in that application…
So far as cleaning pearls, TSP might be a little harsh, but I’d
guess that so long as it’s dilute, it would work safely enough.
Just don’t try cleaning pearls with acidic chemistries…
Any of you real chemists out there know?