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Alum as pickle


#1

Does anyone have experience using alum as a pickle for fine silver?
I’m just learning to solder fine silver pieces for plique-a-jour
enamel jewelry. Some of the joints are not holding well which I am
thinking is because I don’t clean the metal well enough before
soldering. I don’t like using strong acids because I share my work
space and I’m not sure that I can prevent accidents. I did try the
1qt water to 1 tsp alum that I found in Orchid Shop Tips, but it
doesn’t seem to have done the trick. It was in a heated pot for about
an hour. Help?

Thanks G Spiwak @Spiwak


#2

You may want to check the archives for the thread on using
citric acid as a pickle. It is non toxic and is a substance
commonly used in some foods and in cosmetic products.–Vicki
Embrey

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#3

G spiwak,

I have no experience in using other than conventional pickle, so
I can not help you on this. But what you subscribe as joint coming
lose problem, is not a problem of cleaning but a problem of
covering you joint during heating up. An other problem can be
that you are using an oxidizing flame (overdose oxygen) But to
say more I need to now what you are using as heating source. If
you are making Plique-a-jour you need high temperature solder.
These solders contain very less copper, This copper lowers the
melting temperature, and improves the flowing of solder. Lower
temperature solder for silver even contain often a little bit of
zinc, this reaction with the silver and copper oxides so the
joint will be clean inside. You should use a good flux, a good
one is Degussa H. This one is especially for silver at high
temperatures, and solves oxides during soldering.

martin Niemeijer

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#4

Hello Spiwak!

Your difficulty with silver joints “holding well,” could be a
few other problems in your soldering technique. Soldering gold
is much easier than silver. Use baking soda and a brush prior to
a boric acid dip. You can also use pumice powder for cleaning as
well. A pad of scotch brite is real handy also. Be sure your
joints are as tight as possible; silver doesn’t fill well. Above
all, use a paste flux intended for silver at the joint. More
importantly, your flame should be a reducing to neutral. An
oxidizing flame will burn away the flux, create cuprous oxide on
the surface, and cause you to start all over with recleaning the
surface, etc.! Never point the flame directly at the solder.
Instead warm the metal to temperature, and use the temperature
of the metal to flow the solder, rather than concentrating the
flame on the solder and joint. If you need to solder again after
pickle, use baking soda to neutralize any surface pickle that
could remain.

I am not familiar with the use of Alum as a pickle. I would
concentrate on your flame technique and cleanliness. Any pickle
product should work fine. Good luck!

Tim

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#5

Dear G,

Fine silver works just as well in alum pickle as sterling silver
does. I think that your problem is too little alum!! I use a
handful to about one litre of water. I suppose that is a
(female) handful to approx. one quart of water. I must confess
that I never bother measuring it out. The pickle should only
take about three-four minutes to work. larger pieces will take
longer, but certainly never more than ten minutes.

Best wishes
Felicity Peters in sunny West Oz… far away from the Olympics!

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#6

There is certainly something different here! I have tried using
alum, with no success. I bought a bottle from the drugstore, which I
disolved in an approximately one pint beaker. With the solution hot,
I noticed no difference in about a half hour to a normally scaled
piece of sterling. Having something pressing to do, I turned the
heat off, and left the sterling in the beaker. There was almost no
difference in two to three DAYS! Questions: What is the effective
difference between potassium alum and ammonium alum when used as a
pickle? Are there other "alum"s?? As with other chemicals, are
there different qualities of product that could affect the pickling
effect?


#7

Dear G,

You need to use potassium alum. If you buy the commercial grade it is
MUCH cheaper than pure grade. In Australia I pay equivalent of USD
8.00 per 2kgs. A handful to about a quart of water. There is no
science about it… But the mixture must be heated, crock pot, Pyrex
pot on a low heat, use a heat mat underneath. etc I use it all the
time. Brings up the fine silver etc for keum Boo, cleans well etc…
John Burgess would be able to tell us the difference between ammonium
alum and potassium. Good luck

Felicity in West Oz where the temperatures is hitting 35 degrees
today.


#8
 What is the effective difference between potassium alum and
ammonium alum when used as a pickle?  Are there other "alum"s?? 

G’day; potassium alum is potassium aluminium sulphate, KAl(SO4)2 +
water of crystallization, and ammonium alum is ammonium aluminium
sulphate which has the same formula except that the ammonium ion (NH3)
is substituted for the potassium (K) ion. Yes, there are a large
number of alums; chrome alum, magnesium, manganese, ferric (iron) and
etc. All of them generally have the same crystal shape which looks
much like a cube standing on a corner. The reason why potassium alum
(commonly just referred to as ‘alum’) is used as a pickle is because
the molecule continuously breaks up and rejoins when dissolved in
water (dissociation) and ‘ionises’. The sulphate or acid part of the
molecule tends to seize upon any base it finds, and this includes
copper oxide firestain from sterling and low carat golds. The
solution eventually becomes pale blue due to copper sulphate forming.
I don’t know for certain, but I think that ammonium alum should
behave similarly. There is no simple test you can do to determine
the presence of potassium, other than taking a little on a little loop
of very clean stainless or nichrome wire and holding it in the edge
of a hot flame, when a pale violet (hard to see) colour will be
introduced to the flame to indicate the presence of potassium. If
ammonium alum solution is heated with an excess of strong alkali like
caustic soda (lye) a very strong smell of ammonia (don’t sniff too
hard or it will ‘blow’ your head off! - achoo!!) will be produced.

You may have, I suggest, some plain potassium sulphate which doesn’t
ionise as easily as alum, so isn’t much good for use as a pickle.
Add a solution of your ‘salt’ to washing soda or baking soda
solution, and if it is any use as a pickle it will fizz strongly.

Remember the old ‘strike the knob’ fire extinguishers? They contained
a solution of bicarbonate plus either soap or a detergent, and
striking the knob broke a thin walled glass tube of alum solution. The
reaction produced large amounts of carbon dioxide gas which threw the
resulting foam over the fire and put it out - one hoped. Here endeth
the (chemistry) lesson. Cheers, – John Burgess; @John_Burgess2
of Mapua Nelson NZ