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Silver oxide/sulphide


#1
       I recently started making fine silver chains.   After
awhile of wear they appear a little dingy, so I've been using an
ammonia-based dip to clean them and they do come out looking much
better, but not exactly like new.  When I make a new chain, I     
compare After awhile of wear they appear a little dingy, so I've
been using an ammonia-based dip to clean them and they do come out
looking much better, but not exactly like new. 

G’day Anastasia; My first thought is that I should mention again
the fact that silver oxide is an off-white not black or grey, and it
is difficult to make merely by heating silver anyway, so the problem
isn’t silver oxide. Heat blackening of pure (fine) silver is always a
coating of silver sulphide. The blackening of sterling is due to a
combination of the formation of cupric oxide plus some sulphide from
the copper in the alloy, and black sulphide from the silver. Surface
blackening will be removed by immersing in hot pickle. The grey that
sometimes remains is a deep formation of copper oxide which can only
be removed by abrasive methods. Sometimes a slightly prolonged
immersion in Goddards Silver Dip will help.

I believe that the blackening of silver/sterling which forms afresh
after all work has been completed is due to the metal slowly
absorbing traces of sulphur in the surrounding atmosphere; whether
the chain is kept in a box, worn or laid on the dressing table. Such
tarnishing will occur more rapidly in a town rather than in the
country. A dip in Goddards will remove such tarnish quickly.

Another remedy is to put some aluminium metal in a small bowl -
household foil will do - pour in a warm fairly strong solution of
washing soda (sodium carbonate) and drop in the silver. It will
fizz like mad, and the fizz consists of bubbles of pure hydrogen
which react to combine with sulphide and change it to traces of gas.

Because with either of these methods you have interfered with the
surface, the job will propably need to be re polished to restore
it’s brightness

Another remedy is to put he job in fresh pickle and connect the
positive pole of a battery to the job, and the negative pole to a bit
of scrap silver or stainless steel or even carbon rod. This will
literally plate off a very small amount of the surface, taking the
fire stain with it. It will then need to be re polished properly.

It can also be done with either cyanide OR strong nitric acid but I
doubt whether you would want to dabble with either of these
unpleasant chemicals. – Cheers for now,

John Burgess; @John_Burgess2 of Mapua, Nelson NZ