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Technique to prevent firescale?

I’m hearing many differing views on the prevention of firescale. I’d
love to hear your techniques to preventing and resolving this pesky


Make a mix of boric acid and borax (50/50) and add alcohol. Add
extra Alcohol so the whole mixture can be shaken to mix. Then the
item is dipped in the mixed up solution, taken out and the alcohol if
burned to “stick” the boric acid and borax onto the piece. Solder
away with no fire scale…

John Dach

Prips flux, Stop OX II, Cupronil or Firescoff applied per the
directions often repeated here. Search the archives.

James Binnion
James Binnion Metal Arts


Hello Kelli,

Preventing firescale can be accomplished in two ways: use an alloy
that does not react to form firescale, ie. Argentium, or consistently
coat all surfaces with Prip’s flux. That means you turn the piece
over and around to insure the coating of Prip’s flux is complete.
Prip’s flux has been exhaustively discussed, including the formula,
here on Orchid. Search the archives.

Judy in Kansas

Make a mix of boric acid and borax (50/50) and add alcohol. Add
extra Alcohol so the whole mixture can be shaken to mix. Then the
item is dipped in the mixed up solution, taken out and the alcohol
if burned to "stick" the boric acid and borax onto the piece.
Solder away with no fire scale.... 

That works well with gold. In fact, on gold, the standard method of
preventing undue oxidation is exactly that method, or most commonly,
that method using only boric acid, without the borax mixed in. On
sterling silver, the boric/borax mix does not adequately cover the
silver because surface tension effects will have the coating trying
to bead up in areas. it’s better than nothing, but not in general as
effective as one would wish, especially if the soldering operation
is more prolonged, or you’re using a higher melting grade of solder.
In Prips flux, one of the best ways I know to prevent fire stain and
fire scale, the purpose of the sodium phosphate is to act as a
surfactant, lowering the surface tension of the metal surface, so the
flux coating can evenly spread out and coat it without beading up or
pulling away in areas.


Kelli, I have only one word for about preventing fire scale. PRIPPS.
I just mixed up a new batch and it works wonderful on silver. I only
wish I had known about it when I was first starting out. It saves so
much time, even on a simple jump ring solder that I use it every
time I pick up the torch on a silver item. It’s easy to make, and I
use a paint brush to apply it, so it is not so messy as spraying. I
use a small flame to heat the piece and brush it on until the item is
covered in a white haze. To spare you looking in the archives, here
is the recipe. 64 grams borax, 64 grams TSP, the real stuff, 96
grams boric acid and enough water to dissolve it under low heat on
the stove. Try it, it really works, Best regards, Janine in Northern
California where the fires are still burning.


There are several fire scale preventions fluxes on the market and
one you can make yourself.

All of these fluxes work with varying degrees of success…

Be sure you cover ALL SURFACES of sterling with one of these fluxes
if you do not want fire scale.

The fastest way to apply these fluxes is to heat the metal slightly
then spray on the flux with a fine mist sprayer. If the temperature
is correct the flux will form a white crusty coating as it hits the
metal. Too cold and the flux will bubble up or wash away any crusted

The anti fire scale fluxes will act as a soldering flux at joints
however I find it is best to use a very small amount of paste flux
at any joint that will require strength in its application. If you
use too much paste flux it will wash away the anti fire scale flux
thereby causing fire scale to form around the joint.

You should not dread fire scale on soldered items if you use one of
the fluxes. Lets eliminate fire scale. Just about any major jewelry
supply company sells anti fire scale flux.

The amount of fire scale on castings is worse because of the time it
takes to cool the casting below the fire scale forming temperature.
The longer time at high temperature the more fire scale.

If you vacuum cast see my paper on prevention of fire scale on
castings The simple no cost process will prevent fire scale on

I own Four S Laboratories which manufactures Cupronil, one of the
anti fire scale fluxes. We have been manufacturing Cupronil since
1973. I use it and I know it works very well.

If you have any question Contact me off list.

Lee Epperson

That sounds similar to prips flux but minus the trisodium phosphate
and using alcohol instead of water. I currently use boric acid in
alcohol. Would adding borax (which I also have) improve my flux’s
anti-firestain properties?


That sounds similar to prips flux but minus the trisodium
phosphate and using alcohol instead of water. I currently use boric
acid in alcohol. Would adding borax (which I also have) improve my
flux's anti-firestain properties? 

Not unless you pack the borax that will be in the bottom of your
container onto the surface of the work. Borax is insoluble in alcohol
this is why boric acid is used and why methanol works better than
denatured or pure ethanol. Boric acid is only moderately soluble in
ethanol (denatured or pure) and quite soluble in methanol. The
problem with methanol as you know is it is very toxic to breathe,
get on ones skin or ingest so taking advantage of the safer solvent
ethanol is probably the best idea.

James Binnion
James Binnion Metal Arts


I need to chip in here and highly recommend Pripps above all of the
other methods suggested. It has worked a treat for me over the last
few years, and coupled with a finishing process involving medium
greasy compound on a bristle brush results in a great finish.
Argotech and borax on their own (mixed with water or meths) tend to
flake in heating (for me at any rate) giving you a spotty firestain
pattern at the end, Pripps does not.

I would add that applying it can be a bit tedious, as you need an
even coat on silver which is just hot enough to start tarnishing
yellow, but with a bit of practice this is easy to manage. I have
also made myself a very primitive air brush to help out here. It was
put together in a few hours using a glass jam jar as the reservoir
and an old tire inflating foot pump as the air source. The spout for
the pripps is a spare bit of brass pipe (internal diameter of about
2mm) through the jam jar lid and epoxyed in place, and I ran a
length of plastic tube from the foot pump and attached this to a bit
of hard tube which I fixed to the top of the jam jar lid, just in
front of, and blowing across the top of, the brass pipe. Very simple
design, no moving parts, and apart from the need to occasionally
clear the pipe, which clogs with crystallising pripps, this has
served me well for the last three years and is a permanent fixture of
my soldering bench.

Chris Penner

That sounds similar to prips flux but minus the trisodium
phosphate and using alcohol instead of water. I currently use boric
acid in alcohol. Would adding borax (which I also have) improve my
flux's anti-firestain properties? 

Boric acid and borax are very similar in the way they protect the
metal. The big difference between them is that borax melts and starts
to become an active flux at a lower temperature, and burns away as
well, more quickly. The boric acid doesn’t become fully active until
a higher temperature, and it lasts longer and withstands that higher
temperature too. So the combination ends up being a bit more
versatile, starting to protect earlier in the process, and
continueing to do so the same as boric acid alone would do.

The sodium phosphate in Prips doesn’t affect the performance of the
flux in it’s protection abilities, but rather, affects the way it’s
applied and how it initially behaves as you heat up the metal.
Without it, surface tension causes the as-yet unmelted flux coating
to start to melt, but not stick to the metal so well, so it balls up
or pulls away from areas. Sometimes the effect will be a mostly
coated piece of metal with lots of small unprotected little islands.
The metal ends up with fire stain in sort of a leopard’s spots

Even with the sodium phosphate, if the prips flux coating is too
thick or uneven in application, the thicker areas will still tend to
pull away. This happens as well if the metal is dirty or greasy or
something. The reason why it’s normally best applied with a sprayer,
rather than a brush, is that getting a uniform light white crust of
even thickness is much easier. With a brush, one tends to chill the
metal enough so some of the flux goes on wet, then boils. That leads
to uneven little “bubble” like areas with a thicker ring of flux
surrounding a mostly bare little area. Spraying, and keeping the
metal hot enough so the flux dries instantly on contact without a wet
looking stage, gives one the uniform coating needed. The fairly new
commercial product, “Firescoff”, also want’s to be applied in the
same way.

The need for some sort of a surfactant added to the classic boric
acid used to protect gold, prompted another "kitchen chemistry"
product also worth mentioning. At some point (in the 60s) after John
Prip formulated and taught the use of prips flux to prevent fire
scale and fire stain, the Richard Thomas, then head of the
jewelry/metals department at Cranbrook Acadamy of Art just outside
Detroit, started playing around a bit. He wanted a product that would
protect against fire stain and fire scale as does prips, but without
needing that sprayed application, which does sort of waste some flux,
and can make a bit of a mess of one’s soldering pad what with
overspray. A dipped or brushed on product would be much easier to
use. He’d seen a photo, I think in Life Magazine of a pond in which
ducks were swimming. As they approached one end of the pond, to
which a new industrial surfactant had been added, they swam lower and
lower until just their necks were out of the water, kind of like
submarines going under… The surfactant was allowing the water to
wet the bird’s feathers, so they lost their water proofing, and with
it, their boyancy. Made for a dramatic photo illustrating how good a
wetting agent the stuff was. So Richard did some experimenting of his
own with the stuff, called “Aerosol OT-solid”, If I remember it
right. Not a grocery store item, one gets it from the manufacturers
as a somewhat waxy looking solid that can take a bit of doing to get
fully dissolved. But Richard found that a mix of this stuff, with
just plain boric acid and water, gave just the protection he wanted
againts fire scale and fire stain. In honor of the light bulb or bell
or whatever that had gone off in his head when he’s seen that photo
and thought to try and produce a protectant with it, he named this
formula “Ring-a-ding” Kind of an in joke, and testament to Richard’s
wry sense of humor. As a fire stain and fire scale protectant on
sterling, it’s very effective, though the end surface after pickling
is not quite as bright as it can be with prips. But it’s simply
brushed on the surface or dipped. Much quicker than spraying prips.
Unfortunately, there’s a bit down side. The surfactant apparently
also acts in other ways, with the result that the mix is almost an
anti flux for soldering purposes. If you are very careful to paint
it on only an areas which are not being soldered, and use soldering
flux for the seams, you can protect work being soldered. But that’s
difficult, and prips works easier when doing any soldering.
Ring-a-ding ends up being wonderful for annealing, but not much help
in soldering. Given that Cranbrook then emphasized a great deal of
hollow ware work, people were doing a lot of annealing of their
silver between courses of hammer work, so this mix was very much
useful and a time saver. The recipe and instructions for mixing it up
were published at least once in Metalsmith, and for a time, C.R.Hill
co near Detroit, was carrying the stuff. But they tended to mix it
way too dilute, according to Richard. I’ve seen it used at only one
other school, Tyler School of art, where I did my MFA work. There,
though it was available, most students didn’t know about it or bother
with it if they did. A bit too bad, since it really is useful for
annealing processes, even if it’s not good for soldering operations.

The other interesting variant on all this was, I’m told, started
when the purchase of TSP for use in making up prips flux because more
difficult. It used to be available in any paint store or the painting
aisle in the hardware store. Then it’s use became discouraged because
its a phosphate, and in waste water, ends up being a wonderful
fertilizer for algae and other undesired plant life in the water
streams, so phosphates in detergents in general became regulated.
Since then, finding TSP has often prooved to be a bit of a fuss and
bother, and in some areas, almost impossible to find outside of
ordering from a chemical’s supplier at higher cost.

So again, a bit of kitchen chemistry raised it’s head. In this case,
it was by Fred Fenster, who’s the teacher who first taught me about
prips flux in 72. Fred figured that there must be other products out
there, easily and cheaply available, that would work as well as the
pure TSP. He ended up with Cascade dish washing powdered cleaner.
Comes in a nice bright green box, and will get your dishes clean and
spot free and all that jazz. Apparently, it’s mostly TSP, with no
doubt some other surfactants and wetting agents and whatever. It can
be substituted directly for the TSP in the prips formula. Fred named
his variant “Frips flux”.

So now you’ve got the whole story as far as I know it, and my
fingers have had their workout for tonight.


1 Like

Hi James,

Thanks for your reply to my question. I have, however, decided to get
some TSP and make my own Prips flux as so many Orchid members have
said it’s the best flux that really prevents firestain. With so much
sound advice I’d be daft not to take it on board and try the stuff.


Hi Peter,

Thanks for your reply. I noticed that you have answered questions
regarding Prips flux repeatedly both on this forum and others, as
this question regarding firestain and how to prevent it crops up
often. From your responses, I’ve gathered that the trisodium
phosphate affects the surface tension of the flux, keeping it on the
surface of the work to be heated, rather than it pulling away or
balling up and thus exposing your sterling silver to atmospheric
oxygen which can creep deep into the surface, creating firestain.
Keep the oxygen away from the surface and you/we won’t get firestain.
Your explanations are very well put and easy to understand - thanks.

As for availability of TSP, there’s a company on Ebay in the UK that
sells many lab/technical grade chemicals and other household
products. I buy my sodium bisulphate, boric acid, borax from them and
I noticed yesterday that they also sell TSP so in the UK it’s not a
problem. If anyone in the UK wants a link, contact me offlist as ebay
links are not allowed on Orchid.

Thanks again Peter.


Thanks for your reply to my question. I have, however, decided to
get some TSP and make my own Prips flux as so many Orchid members
have said it's the best flux that really prevents firestain. With
so much sound advice I'd be daft not to take it on board and try the

Good plan, I would be lost without it.

James Binnion

Hi, Is the TSP you refer to trisodium phosphate? How long can you
keep a batch of this? Are there any special conditions needed to
store this?

Thanks Steven

Good plan, I would be lost without it. 

I’ve been daft enough to have been reading about Prips for the last
year but have not yet used it. You can tell I’m resistant to change
(read stubborn) and have only recently noticed my patches of
firestain as my finishing has improved to the point where firestain
shows up clearly to those who know what it is and what it looks like.
It’s one of those things that once you see it, that’s all you see,
and it detracts from the beauty of whatever piece you’ve made once
you see that telltale patch of firestain.

I’ve ordered my TSP and am looking forward to a bit of kitchen
chemistry to make my new flux. I do catch on to good advice
eventually. Thanks for your continued helpful advice James.

PS. I hope your new venture is going well.

Alright, someone enlighten me.

What is TSP and prips flux? Details for those of us who missed this


the tsp is tri sodium phosphate. the solution will keep indefinitely
but this is a saturated solution and salts will crystallize out as
water evaporates. Add little water.


At the bottom of this email will be a link for orchid archive. I’ll
place it above my sig line. There are a lot of discussions on these
and if you simply type in either TSP or prips flux at the archive
point (make sure to select the entire archive or something,
otherwise it’s not looking at discussions.) The folks here sometimes
have time to do it, sometimes don’t…but imagine having a busy day
of work you love and having to explain (5 or 6 times I recall since
I’ve been on here at least, maybe more) what pripps flux is and what
made of etc.

You can also review the entire discussion there.

Kim Paluch


In Sarah Macrae’s book “Designing and Making Jewellery”, on page 25,
she describes a product called FM Solution. This is a firescale
prohibitor. The recipe calls for Sodium Acid Phosphate and I am
having some difficulty obtaining this item. Could someone please give
me an idea as to a product or products that could be substituted for
this product? Is it the same as TSP, and if so could it be
substituted into the recipe with the same results, and in the same
amount without it causing the recipe to be compromised?

Thanks for your input.
Bea Morris