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Blue Pickle


G’day; I have noticed that the term ‘blue pickle’ has cropped up
several times lately. May I point out that this - in well used
pickle - is almost certainly due to the presence of copper
sulphate. The blackening of strongly heated sterling is due to
oxidation of a little of it’s copper content. Allowing it to
stand or heating it with sulphuric acid or Sparex (sodium acid
sulphate, sodium bisulphate) allows the copper oxide to dissolve
in the acid, producing blue copper sulphate. If iron forceps are
used to get silver jewellery pieces out of the pickle bath,
expect a red stain of copper to be plated on the silver due to
electrolytic action between the dissimilar metals. But this is
easily buffed off. If nitric acid acid is used to pickle nickel,
expect to see a greenish colour of nickel nitrate; although some
nickel alloys also contain a little copper. My suggestion is that
the pickle should not be allowed to become more than very pale
blue; Sparex is cheap enough to discard frequently, or use the
sodium bisulphate sold as a pH adjuster for swimming pools - that
is very cheap indeed and is the same stuff. I would also suggest
that brand new pickle which is blue contains a harmless blue dye.
Sodium bisulphate is colourless –

    /\      John Burgess
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(_______) Mapua NZ is a pleasant spot even in midwinter