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G’day: I’m a bit academic here; I don’t like the term
’oxidising’ when ‘blackening’ is meant, referring to jewellery.
You see, silver oxide is white and a bit difficult to make merely
by heating. It would be more accurate to use the word,
‘sulphiding’, for practically all the silver blackening methods
in jewellery depend upon sulphur, for silver sulphide is dead
black. The substance known as “liver of sulphur” is potassium
polysulphide. It is a solid which attracts moisture from the air,
and deteriorates fairly quickly when wet, to produce hydrogen
sulphide gas (rotten eggs) and finally leaves potassium sulphate,
which isn’t much good for blackening silver. However there are
several allied compounds such as ammonium polysulphide; a yellow
liquid which used to be sold in joke shops, contained in fragile
glass bulbs and which, when kids, we bought to crush in school,
the cinema, or in pompous company because it really stinks of
rotten eggs. (!!!) [evil little blighters] Anothur sulphur
compound is sold in plant or gardening shops as a yellow liquid,
and one dilutes and mixes it with lime to spray on shrubs, etc as
a cure for fungus. Most of these shops sell it as "lime-sulphur"
It is probably calcium poly-sulphide and is not only cheaper than
’liver of sulphur’ but can be bought almost anywhere, works just
as well, and smells just as bad. On a ring or similar (or low
carat gold) item which will get a lot of rubbing the blackening
will quickly wear away unless in a recess. Pickle or silver
cleaning dip solutions will also remove it. Indeed, some Orchid
members will remember that a while ago I was asking about a
substance called niello which is an ancient black recipe for
putting into recesses in jewellery for just that purpose.
Unfortunately it is not only difficult to make, but produces
heaps of toxic fumes of sulphur dioxide, a very choking gas. I
did try it, but decided that I would use an epoxy resin coloured
with black pigment. (my ancient lungs can only take so much)
Black, hard, epoxy works well, but only in fairly deep recesses
in the work. To use all these sulphur substances for blackening,
you dissolve a little of the potassium sulphide - or whatever -
in warm water, and drop in the freshly-pickled item, leave for a
few minutes, then dry and buff gently. So there you are, more
than you ever wanted to know. I just can’t keep my nose out of
things, can I?

   / /    John Burgess, 
  / /
 / //\    @John_Burgess2
/ / \ \

/ (___)