I come from an industrial chemical research background, with a
strong safety culture. Making jewellery is a hobby for me.
Sodium bisulphate solution can be regarded as chemically equivalent
to a solution of sodium sulphate in sulphuric acid. The solution
contains both sulphate and hydrogen ions, just as sulphuric acid
does. As used in jewellery work for pickling it is the equivalent
of dilute sulphuric acid.
I use sodium bisulphate solution for pickling. I use it cold. I
quench metal in plain water before putting it into the pickle.
Quenching hot metal in the pickle does produce a little puff of
vapour, which will contain small droplets of the active pickle
ingredient. My reason for quenching in plain tap water first is to
avoid risking getting these small droplets onto nearby tools and
other objects in the same room. With the sizes of object I work
with, and the small number of times I quench, it would not be a
health hazard. I have a lid on my pickle pot, mainly to keep dust
out of it. In other work situations it (vapours from quenching)
could easily become a matter of concern though, as for example more
frequent quenching, or when quenching larger objects. It is nothing
like strong mineral acid mist that has been discussed here though.
Neither is it being breathed for an eight hour shift.
Warm pickle works much faster than cold. It should be warm though,
not overhot. In a hobby situation there is no need for the “boiling
out” sometimes mentioned in older books.
In a professional workshop (by which I mean manufacturing for sale)
there is likely to be a much higher throughput, and real pressure
for faster work. There are also Health and Safety regulations in
most countries too, and these will address issues such a vapours and
the possible need for air extraction.
Citric acid has been mentioned here, and it certainly is safer than
dilute sulphuric acid. There could be a possible concern with
"nasties" growing in it, if it’s cold and unused for some time.
Citric acid is nothing to do with vitamin C.
Sorry, but all sulphur containing compounds do not attack tooth
enamel. The element that sulphur seems to be being confused with is
phosphorus, and it is true that match workers suffered terribly, the
condition being known as “phossy jaw”. It was caused really by the
pure element. Compounds are a different matter. But, don’t imagine
that there is a problem with all phosphorus compounds. Many popular
fizzy drinks contain phosphoric acid. I don’t drink them, but not
because of the acid. And please don’t start to worry about the
phosphorus in TSP used to make Prip’s flux…
I realise that to folk who haven’t had a chemical eduacation it can
all be a bit confusing, especially with somewhat similar sounding
names. I sincerely hope that this may have gone some way to
clearing up some of the confusion, and perhaps allayed a few fears.
Kevin (NW England, UK)
