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[Deja Vu] liver of sulphur


#1

G’day. This is all in the archives, but we’ll repeat it for
convenience sake.

Liver of sulphur (potassium polysulphide) does NOT form
compounds with gold, so it is futile trying to blacken better
than 18 carat gold with it, and the blackening that does occur
with 18ct isn’t very satisfactory. When the sulphide seems to
blacken gold, it is actually the copper and/or silver component
in the alloy that blackens, producing a very thin layer of black
copper or silver sulphide. I have blackened high carat gold by
careful copper plating, buffing off the copper where black wasn’t
required, immersing in a fresh, warm solution of the ‘liver of
sulphur’ and after drying, subsequently gently heating to achieve
a better bond. All over blackening of finger rings is a bit
pointless, for with constant wearing the blackening will wear off
in places over a period of around 6 months , and tend to look a
bit tatty.

Why does the sulphide solution need to be fresh? Because the
polysulphide reacts with the water and air to produce firstly
sulphurous acid, then sulphuric acid, and potassium hydroxide,
then these combine to produce potassium sulphate and water.
Neither of which is much good at blackening. Light shining on
the solution also helps destroy the sulphide. It might last
longer in a brown or dark bottle, but a pea-sized piece of the
solid polysulphide is quite enough to blacken quite a lot of
rings, etc, doesn’t cost very much, and rapidly breaks down on
it’s way to the sewage treatment plant. Why warm? Because
(almost) all reactions occur better at warmer temperatures.
Including the bonding of the copper/silver sulphides with the
alloy.

No apologies for getting a bit academic and ‘technical’, because
I do hate it when people tell you do, or not to do something
without explaining why. Don’t you? Cheers, –

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/ /__|\ @John_Burgess2
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At sunny Nelson NZ 31C on Sunday.