I use 10% sulphuric acid solution and change it when it begins to have a
tinge of blue from the copper in it (put white paper under your glass
pickle dish.) If you use a pH indicator even on quite dilute acid it will
still read about 2 - 3 as sulphuric acid ionises very freely in water.
This acid is so cheap that you can afford not to keep it too long, and the
same, of course goes for sodium bisulphate. Did you know that the latter
is a byproduct in the manufacture of hydrochloric acid? The sulphuric
acid is heated with salt and the resultant HCL gas is passed into water.
Which is why bisulphate (NaHSO4) is - or should be - dirt cheap; other
than for jewellers it has few uses.
/ / John Burgess
Hi John, a couple of notes to add, sulfuric acid solutions if left on their
own concentrate (or evaporate) until they reach 49% acid which is
hazardous, not to mention the storage issues of the containers and the
possibilities ofr breakage while handling the bootles (seen this-always
hold the bottle with two hands, one underneath…) The reason to use Sparex
(sodium bisulfate) is that it is a slat and dissociates in water to make a
constant dilution of sulfuric acid, more dissociates as the acid is used in
reacting with copper oxides maintaint the dilution. Sodium bisulfate is the
main ingredient in toilet bowl cleaners (Vanish for example) which may say
something about disposal. It is also called PH reducer or swimming pool
acid and can be bought far more cheaply from the swimming pool supply than
the jewelers, if you want more even cheaper janitorial suppliers sell drums
for toilet cleaning. It is also used for picling steel in the steel
Note that a dilute solution of Alum (from the supermarket) (perhaps 30
grams or so (1oz) to about 3.8 liters of water (1 gallon) is apparently all
that is needed. The solution does not outgas as much as a sparex one and
copper flashing does not occur if you put your steel tweezwers in -or so I
hear. I’m used to Sodium bisulfate and bnuy it at the swimming pool supply.
Box 1624, Ste M
Calgary, Alberta, T2P 2L7