Someone recently told me that alum can pickle off firescale. Anyone
Please note, this is not a question about how to avoid creating
firescale (or Firescale 101 you could say…which has been discussed
at great length before) as I do various things to reduce it,
argotecting the backs and so forth.
As an enameller, I spend a lot of time tediously abrading the
firescale off the backs as that suits the quality I’m aiming for.
(Apparently in the US you care far less about the backside of pieces
but that’s a different kettle of worms!) I have used fine silver,
935 and 965 silver, but they are all too soft for much of my work and
I’ve gone back to sterling.
Alum can definitely remove cuprous oxide, but it is the more
tenacious and tedious cupric oxide that’s in question. The advice was
to use a warm saturated solution of alum in water, apparently quite
On pieces with heavy soldering (eg boxes) : before enamelling, I put
the piece through 69% nitric acid - nasty stuff - but it gets the
firescale off. [Nitric turns the firescale black and you can brass
brush it off, then redip until no more appears] A safer and more
gentle way would be great.
A metallurgist advised that high vol. hydrogen peroxide combined
with ammonia would work, but I have not done the tests.
Here is what he said:
Hydrogen peroxide from the chemists (pharmacy) plus the strongest
ammonia you can buy. Goggles, tongs & gloves of course, mixed in a
glass container with a lid ( eg Pyrex ). This mixture gets hot and
boils (ventilate!! or work outside). He advised experimenting to find
the best strength for this solution, you can reduce it with water.
Any on this method, alum or anything else which removes
firescale would be great, thanks.
Tamizan, Bristol UK