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Alum as a pickle for firescale

#1

Someone recently told me that alum can pickle off firescale. Anyone
have any

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
slow.

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
www.tamizan.com

#2

Hi Tamizan,

Someone recently told me that alum can pickle off firescale.
Anyone have any

I use sodium bisulfate solution bought from a chemical supply
company. It is the main ingredient used in Sparex #2 but without the
horrible binders, etc which make it a horrible sludgy mess. It is
also the equivalent of what pool owners use to reduce the pH of
their swimming pools - pH down. It is chemically related to the
alum-type pickles.

You say that nitric acid pickle “gets the firescale off”, but then
you say that it turns it black so that you can brass-brush it off. So
really it’s identifying where it is more than removing it? If that’s
the case, then my pickle would seem to be doing the same thing - BUT
over a matter of weeks. I’ve recently found that little bits and
bobs that I’ve chucked in my pickle pot and essentially discarded,
have later shown black patches.

The problem is, that with a weak pickle such as alum, even if it
does identify patches of firescale/firestain (I can never remember
which is which), it may take up to a few weeks to do so, and who’s
got time to wait weeks to move onto the next stage in a piece’s
fabrication?

Hopefully someone else can shed more light on your question.

Helen
UK
http://www.hillsgems.co.uk
http://helensgems.ganoksin.com/blogs/

#3

Tamizan- Have you tried good old fashioned Sparex? It’s available
through most jewelry suppliers and works just great on fire scale.
I’ve used it on enamelled pieces with no adverse effect. As to how
American jewelers finish the backs of their pieces… Please go to
our web site www.timothywgreen.com. Click on “pendants” and you will
see a couple of examples of the backs of our pieces. We take special
pride in azuring our work, hiding gemstones or special little designs
on the insides of our rings and on the backs of our pendants,

Have fun and make lots of jewelry.
Jo Haemer

#4 
Someone recently told me that alum can pickle off firescale.
Anyone have any

Alum will work as a pickle just like sparex or citric acid, but will
be no better at removing fire stain than either one.

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,

I do not know if this will work or not but these are both highly
reactive chemicals. Hydrogen peroxide at high strength can cause
instant fires or explosion if it contacts flammables. And we have
had recent long discussion on high strength ammonia so i will not go
back there. Anyhow I would probably want a lot more information
before trying that suggestion.

Jim

James Binnion
James Binnion Metal Arts

#5

Hi Jo,

Tamizan- Have you tried good old fashioned Sparex? It's available
through most jewelry suppliers and works just great on fire scale.

Another very good pickle is Ph Minus or Ph Down. It’s sold to adjust
the Ph of the water in swimming pools & spas. Depending on where you
live its available in grocery, drug, swimming pool supply stores &
home centers. A couple things that make Ph Minus/Down nicer than
Sparex is the cost (its less expensive) & there’s now brown scum that
sometimes occurs with Sparex. The Ph Minus/Down is the same thing as
Spare (sodium bisulfate) without the scum producing ingredient.

Dave

#6 
I do not know if this will work or not but these are both highly
reactive chemicals. Hydrogen peroxide at high strength can cause
instant fires or explosion if it contacts flammables.

Reactive Metals has a paper on hydrogen peroxide pickle that can be
purchased (.50). Click on Publications at this link:

http://www.reactivemetals.com/documents/RMSVol1.3-19-09.pdf

I haven’t read it myself and don’t know if it answers questions
about removing both of the firestain copper oxides, but I would be
surprised if it didn’t deal with safety issues. Maybe Bill Seeley
will comment here?

Beth

#7 
http://www.reactivemetals.com/documents/RMSVol1.3-19-09.pdf

Beth, Bill’s paper deals with the use of 3% hydrogen peroxide, a
relatively safe chemical combined with a small amount of weak acid
like pickle or vinegar to remove fire scale from copper alloys and
it does a great job for that purpose. But the posters description of
generating a lot of heat led me to assume the hydrogen peroxide in
this case would be the higher concentration variety (30%) that is
quite dangerous. It is used as an oxidizer in some types of liquid
rocket fuel and must be handled with great care.

This is like the recent ammonia thread where the concentration of
the chemical makes all the difference in the world.

A little vinegar in your salad is a wonderful thing but in its
highly concentrated state acetic acid (vinegar) will burn you
severely.

Regards,
Jim
James Binnion
James Binnion Metal Arts