It constantly surprises me how many people who’ve worked for
quite a while with silver seem to still have significant problems
with fire scale on sterling.
hey folks, it’s not hard to prevent. The cure is called pripps
flux, which you spray coat your pieces with before any and all
annealing or soldering operations. I first wrote a quick
article about pripps flux several years ago, and it’s proved
useful enough that from time to time I republish that
description. It sounds as though some in this thread could use
it again. here tis. enjoy. (sorry about the odd formatting of
the article. I cut and pasted it from a copy with fixed line
lengths into my newsreader…)
Peter Rowe
Pripps Flux
Pripp’s flux is a mix you make up yourself, and it works pretty
much the same as a borax coat, which is the older and more
traditional method. Classical silversmiths would often go through
several sequences of “burning on” a borax coat before annealing
or soldering, but it doesn’t work quite as easily or as well as
Pripp’s.
I’ve been a gold and silversmith since college, and learned
Pripp’s from Prof. Fred Fenster at the University of Wisconsin,
who proclaimed in that 1972 sophomore class that at other schools
people sometimes complained about firescale, but “here at U.W. it
never gives us a problem”. This, by the way, was taught from the
first moment we were shown how to light a torch, just to give you
an idea of how important and basic a technique Fred felt it was.
It’s named after Jack Pripp, who taught at Rochester for many
years, and is considered one of the fathers of the American
metalsmithing community.
To make it, you will need: a quart of water, 120 grams boric
acid, 80 grams each TSP (trisodium phosphate) and borax. Boil to
dissolve it (you might have to add a little more water. It’s the
3:2:2 ratio that’s important, not the concentration.). The Borax
you can get at the supermarket, in the laundry area. (Borateem
is just borax- the little green flecks they put in there too
don’t seem to matter). TSP (trisodium phosphate) is a strong
alkaline cleaner often used in cleaning walls and the like before
painting. You can usually get it in paint or hardware stores, but
be sure it’s actually trisodium phosphate. Because it’s rather a
caustic (though reasonably safe) material, some stores carry a
substitute, which may be confusingly labeled. (eg.TSP brand
wall-cleaner no longer contains TSP.) Read the box carefully.
The substitute doesn’t work for this purpose. If you happen to
have a chemical supply house around, you can also use disodium
or monosodium phosphates. But the trisodium formula seems to be
the most common.
You apply it (and this is an important detail) by spraying it on
the silver while gently heating the silver up enough so the spray
dries on contact, as opposed to hitting as a liquid and
bubbling/boiling off. The best sprayers by far are the cheap
little two-tube-with-a-hinge mouth atomizers that ceramics folks
sometimes use for applying glazes. It gives a much finer and more
uniform spray than any sprayer bottle I’ve seen, and cannot
clog.
To use it, you’ gently brush the metal with the flame, then with
quick short puffs on the sprayer, put the Pripp’s flux on a
little at a time. The idea is to coat the entire piece with a
thin white crusty coating, thick enough so that reflections from
the metal are no longer visible, but no more. Be careful, as you
do this, neither to let the metal cool so much that the flux
stays liquid (it doesn’t coat evenly then), or that the metal
gets so hot that it starts to discolor. It’s easy enough, but
takes a little practice at first. Coat all the parts of your
assembly, then let them cool, set up the joint, and with the
addition of the smallest amount of additional soldering flux only
in the joint (see below) and solder, do the soldering job.
Pripp’s is a much less active flux than the paste fluxes, and
doesn’t burn off easily (though with enough overheating you can
do it), so it gives continuous protection, and thereby completely
prevents fire scale. It will work as a soldering flux all by
itself IF your metal and solder are both completely clean before
you start, and if your heat control is good. Paste fluxes such as
the “Handy” or Griffin brands, oddly enough, seem to provide
little or no firescale protection. In fact, with some metals
(like white golds) you’ll find the firescale is worse where the
flux was. This is why you don’t want to use much, and should keep
it only in the join area. But they are so very active while still
fluid that they greatly promote solder flow, so many of us use
them anyway. Battern’s self-pickling flux is somewhere in
between- it lasts longer and doesn’t give quite the fire scale
problem, but also doesn’t protect quite as well.
In my work, for simple repairs to already-made silver jewelry, I
usually just use a boric acid/alcohol coat, solder with paste
flux, and clean up later, as most of these pieces already have
fire scale, and for a single quick ring shank solder job or what
have you, it’s not worth the trouble to bring out the Pripp’s.
But if I’m making something from scratch, then (with a few
exceptions), every last annealing or soldering step is done with
Pripp’s coating everything.
The added time and bother is more than paid back when it’s time
to finish the piece- when there’s no surface oxide and no fire
scale, then the piece can be polished out as easily as gold
work. This coating, if you are careful and don’t pickle it off
after soldering, can usually last through several soldering
cycles; so for some complex assemblies; if you’ve got everything
fitted before hand, you may only need to coat the parts once for
a number of sequential soldering steps. Also, since the sprayers
tend to cover rather more area than just your silver (like the
tools and bench areas behind your soldering area), you will want
to set up some sort of simple shield behind the area you’re using
for spraying on the flux to catch that over spray. This saves a
lot of mess.
Peter Rowe