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Grey stains on silver


#1

Hello, I would like to know why most of the time do I have grey
stains on my silver pieces? Is there a way to avoid these stains?
I have the same problem with casted silver : grey stains appear
when I polish the pieces. I use 3M paper to rub out them, but
they don’t want to go!

Thank you for your answer,
CAMILA, from Buenos Aires, Argentina


#2

Camila, the grey stains are commonly known as firescale, less
commonly known as fire bloom. To avoid in the future, you have to
reduce the oxygen in soldering and casting. For soldering use
something with a borax or boric acid in the composition to coat
your piece before working. Reduce your oxygen mix on your torch.
If there’s a problem getting the metal up to the proper
temperature, use a larger tip. When casting, use a pinch of
borax or boric acid (presuming you’re doing your melt in a
crucible), and reduce the oxygen mix in the torch. If you’re
using scraps for your melt, also use a carbon rod which has been
dipped in borax to stir the melted metal, bring up to heat again
before casting into your mold. If you are doing vacuum casting,
you’ll need to get additional help from someone who does this
type. Good luck! K.P. from Wyoming


#3

Camila,

It's called firestain/firescale, and it's a layer of cupric

oxide that builds up within the structure of the metal itself
when the piece oxidizes. A “skin” of fine silver comes up to the
surface of the metal when you quench it, so you don’t see the
firestain until you polish through the fine silver…

Having said that, you can help prevent it by using a boric acid

solution (boric acid and methyl hydrate, mixed in quantities and
then you dip the piece in it and burn off the alcohol), LOTS of
flux, and use a reducing flame as much as possible. It gets worse
as you reheat the metal several times, so try and do your heating
in one shot.

If (I should say when.. :) happens to everybody) you get it,

work it out with 400 or 600 sandpaper, which is fine enough to
let you see it but gets it out relatively quickly. If it’s on a
part of the piece you can’t polish, I recommend Liver of Sulfur
if it suits the design of the piece. ZAM (a cut and polish
compound) also helps.

Hope this helps -- Kieran

#4

This sounds like “fire scale” and I don’t know of any way to
avoid it. Do you use a tumbler to polish? I do, and find that
stainless steel medium in a vibrating polisher gets rid of most
fire scale. Hope this helps!


#5

I sometimes get these stains when cleaning in the ultrasonic
that has gotten really hot. I think it is a form of tarnish. Very
annoying! I remove them with a a very fine cratex polishing
wheel - the pink one - in my flex shaft.

Cheers
Virginia Lyons
Metalsmith


#6

Has everybody forgotten about Pripps flux? I find prevents all
the fire scale from star to finish. We just had a thread on it
not to long ago. Should be in the archives. Janine In Redding Ca


#7

The ‘grey stain’ that you are describing is called fire scale.
The way to prevent having fire scale on your work is to cover
your whole piece with flux (or borex) before soldering, and not
only around the soldering area. If you still get fire scale try
to aneal the piece softly and than drop it into water for a few
times and the fire scale should be reduced.

Hope it helps
Iris Saar Isaacs, Australia


#8

Hi Camila

The grey stain on the silver is called firescale. It’s copper
oxide (or is it cupperous oxide?). It can form on sterling silver
when it is exposed to high temperatures such as in casting or
soldering. You can minimize its formation by thouroughly coating
a soldered piece with paste flux and using a reducing flame
instead of an oxidizing flame. A reducing flame shows a little
yellow at the tip. The new de-oxidizing silver alloys should
eliminate firescale in castings, since they don’t contain copper.
I don’t know of an easy ways to remove firescale other than
sanding and polishing through the layer. Best of luck, Tom Tietze
-The Artisan Workshop


#9

What you are describing is probably fire scale. It is not
really visible until you start to tripoli or polish the piece.
Some oldtimers explained to me that if someone who worked in
silver told you they never got fire scale, they were either
fibbing or were doing wire-wrapping. In any event, I use white
diamond tripoli to remove the fire scale. It has always seemed
senseless to use sandpaper and then use the tripoli when it
could all be done by just using the tripoli. I have found that
if the piece is heavily stained with fire scale, oxidation with
liver of sulphur does not cover it and it is extremely hard to
solder another piece to it (i.e., ring shank, leaves, etc.).

I constantly reinforce to my students that a “little bit of fire
scale” is unacceptable. It takes just a little more work to
bring up the purity of the silver. Of course, some of them have
totally covered the whole piece with fire scale and don’t notice
it until they break through it a little bit. I also stress that
file-finishing or using a satin finish does not cover it and it
shows carelessness or lack of craftmanship.

Good luck.


#10

Have you ever heated a piece of sterling with flux on it and
then let it cool without quenching. The area covered with flux
stays white while the rest tarnishes. The area under the flux
was protected from tarnishing because it was not exposed to
any/or as much oxygen, therefore it didn’t oxidize. It is the
copper in the sterling that causes the fire scale and tumbling
with stainless steel shot will only hide it unless your liquid is
very caustic or acidic so that the silver surface is removed
below the fire scale. The only way we have found to 95% prevent
it is to use a boric acid and borax mix coating the surface and
forming a shell over the sterling during soldering which is then
removed in a hot pickle solution. Be careful quenching a piece
too quickly since that could cause stress fractures.

These are my own observations taken from 25 years of silver
jewelry making, and 100’s of hours of polishing to remove fire
scale.

Pickle or Sparex is an acid and should be handled as such.

Hope this helps
Fred Krauter Specializing in Jewelry techniques
Gristmill Craft School and Hand cut stones
P.O.Box 453 http://www.Handworks.com
Doylestown, PA 18901 @Fred_Krauter1


#11

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


#12

Peter, I have read in it’s entirety (and printed out the 3
pages) your Fred Fenster, Pripp’s anti-firescale formula and
utilization instructions. You are to be complimented for taking
the time in dedicated sharing of your talents. Blessings, and
keep your sage counsel available for those of us that thirstingly
drink at the Orchid oasis!


#13

Speaking of firescale, have any of you used any of the firescale
resistant silver alloys currently on the market? Several major
alloy manufacturers offer them, and they’re supposed to
significantly reduce the amount of firescale that occurs. But
manufacturer’s claims are often one thing, actual experience
another. Have any of you tried one of these firescale free
alloys? If so, what was your experience? I look forward to
hearing about it!

Suzanne Wade


#14

Peter, Thanks again for all your valuable I have
been using Pripps with great success ever since I found your
formula. I only wish that I had found it twenty years ago. The
only problem I have is that I can’t find one of the sprayers you
mention. The 99 cent one that I have been using works OK, but
today it clogged and I ended up using a brush to paint it on.
Any hints on where to look for a hinged sprayer? Thanks again, I
would like to meet you if you ever get down to Redding. Janine


#15
    The only problem I have is that I can't find one of the
sprayers you mention.  The 99 cent one that I have been using
works OK, but today it clogged and I ended up using a brush to
paint it on. 

they are made for ceramics use, for spraying on glazes. You
could probably make one easily enough if you really can’t find
one. Email me if you need more details on how they look.
Another possiblity is a type of air brush that sometimes is
available. The key feature is that it be an external mix, so
the 'brush" handpiece blows a jet of air across a plain, open
topped vertical tube, which sucks the fluid from the jar it’s
attached to, instead of the more common internal mix ones. The
external mix air brushes are really cheap types, often sold for
hobby level simple work, like painting crafts. I think I saw
one in harbor freight the last time I was there… More bother
and setup than a mouth atomizer, but it would work. If you do
use an ordinary spray bottle, then the key is to not keep the
flux in it, but to put it in when you need it, and clean it back
out when you’re done. then residues don’t have a chance to dry
in the nozzle and clog it.

Peter Rowe


#16
   Speaking of firescale, have any of you used any of the
firescale resistant silver alloys currently on the market? 
Several major alloy manufacturers offer them, and they're
supposed to significantly reduce the amount of firescale that
occurs.  But manufacturer's claims are often one thing, actual
experience another.  Have any of you tried one of these
firescale free alloys?  If so, what was your experience? I look
forward to hearing about it! 

The fire scale free casting alloys are generally designed for
casting, rather than for fabrication. In that use, they work as
described, giving you essentially fire scale free castings. But
they have some drawbacks. They are softer than sterling, and
don’t take to heat treatment as well either. Plus, in addition
to being fire scale free, since they contain no copper, they
also don’t tarnish so much. fine as far as it goes, but when you
bring out the liver of sulfur to antique the pieces, you’re in
for a nasty surprise. Doesn’t work so well.

They do have their uses, and for some items, are a god send.
But I generally prefer sterling. Nicer working metal, more
durable when done, and i’m used to it…

Peter Rowe


#17

Peter Rowe: I really need to agree with this statement. I read
your article about pripp flux 6 months ago and tried it. It is
amazing at the time it cuts down on fire scale. The only problem
I had was trying to find something to make it spray from. Still
looking, but you did explain better what I need in your last
instructions. Thank again for the info. Someone also suggested
using citri-sol as a wax solvent. I think it was J. Henkel. If
so it works great on the wax let alone cleaning other things up.
So to sum it up. Thanks to all for Orchid. I could never be
without it. Ron


#18

Hello Susan,

I have been using united precious metals firescale resistant
alloys since they originaly came out.(they are the originators).7
or 8 years ago, the metal had more of a greyish tint , but no
firescale unless the metal or flasks were cast to hot.

Over the years, they have improved their alloys,and the alloys
they now sell are a perfect match .I personally buy the alloy
instead of the prealloyed silver and the reason is that when i
cast 1000’s of oz. of silver , there is a big cost savings. In
small quantities… probably not much. This metal is much easier
to cast… far more forgiving as far as porosity…if there is
any, it polishes out. however, it takes a good caster to
determine the proper flask casting temperature of the items
being cast.This is where most casters make their mistakes…also
the type of casting equipment… digital oven controls(they are
more accurate )Vacuum casting instead of centrifuge etc. there
is a big difference in the quality .

All the items that i do (big volume as well as custom

castings)for my customers are polished to a mirror finnish.This
is the most difficult finnish to achieve .From Trophy Handles to
12mm wide band rings ,to filigree parts, we have had no problem
with united’s metal.

The alloy i use is the S88 alloy.(united’s tel.800-999-3463 ask
for Karen) I hope this helps you.If i can be of further
assistance, or if you need castings, please contact: Dan

http://www.racecarjewelry.com
tel: 401-461-7803


#19

I work mostly in fine silver so I usually don’t have firescale
problems. Sometimes I use a firescale preventive but I don’t like
the fumes. My problem is if I get heavy handed with the solder
the solder creates stains. I will sand and sand and sand and it
seems like it has gone away but when the solder “tarnishes” I have
stains again- The fine silver is always fine.Any suggestions on
how to handle “dingy” solder stains?

DeDe


#20

Hi all - Cindy Eid, who teaches at DeCordova Museum in MA and at
a number of other fine arts schools, has told us to try one of
the little metered nasal spray bottles – the ones you get with
prescription meds like Vancenase (19 g capacity). They’re small,
can be operated with one hand, and have a very fine spray
pattern. Once one gets over the initial revulsion and cleans an
old bottle out, it seems to work very well.

Cindy is a fabulous teacher, if you get a chance to study with
her.

Best

Ann D
@agd