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Grey "ghosts" on sterling silver


#1

Can anyone tell me why my students and sometimes myself are
getting these 'ghosts–gray coloured shadows on our silver when
polishing. We are using a hand torch of propane gas ( due to a
lack of anything else safe here in Saigon) which is difficult to
control into a small flame. I have tried covering the piece in
flux (borax based) but no help. I’ve sanded down a layer to
get rid of it but not all pieces are designed for this to be an
option. HELP!! Sharron, in hot Saigon.


#2

Hello Sharron, It does sound like fire scale from overheating.
The copper is separating from the silver and flowing to the
surface. Fire scale usually shows up in the final polish. The
torch is not the problem. I’ve seen fantastic delicate work done
with the hand held propane torch. Steve Ramsdell


#3

The ghosts you describe are what I know of as fire scale. It
comes from over heating during soldering which I believe can’t
always be avoided. The flux you use can prevent it. Try another
flux. Look up Pripps flux in the Orchid Archives. You will find
a recipe that anyone will find easy to make. I use it and it did
away with my grey ghosts. Net


#4

Sharron, You are experiencing what is called fire scale.It is
very hard not ot get and harder still to get rid of.If you can
evenly heat your pieces and not heat them beyond the point where
your solder "flows"It will help Pickle well.If the fire scale has
not penetrated the top layet of silver too deep you can buff the
fire scale off using tripoli or white diamond.There are many good
suggestions in the orchid archives. Best J Morley Coyote Ridge Studio


#5

Dear Sharon Discussions over the topic of " fire scale’ and the
ways to prevent them took place few times over the last couple of
years at the Orchid forums. You can retrieve the threads by
running a keyword search.

Check out the following address to learn moRe:

http://www.ganoksin.com/orchid/archive/

Best Regards
Hanuman

Dr. E. Aspler
aspler@ganoksin.com
Managing Director
Ganoksin Jewelry Co.,Ltd

Webmaster Ganoksin Online

ICQ # 258 49350


#6

Dear Sharon Sounds like the deadly fire scale is striking
again…there are many postings about this topic ! Most opinion
is that firecoat or pripps flux takes care of the problem and
this has been my experiance you make fire coat by mixing borax
and or boric acid in alcohol and coat the piece with it then
light to burn off the alcohol leaving an oxygen barrier so the
scale won’t form …as for pripps flux the formula for that can
be had in the archives here or T McCreight’s book and many many
more places Hope that helped Ron

PS. Try to keep the heating time as short as possible as that
will also help


#7

Sharron, I had some major frustration with firescale, until a
friend recommended using a cratex wheel to remove the stuff. It
is also possible to heat, pickle and quench the piece multiple
times to bring a layer of fine silver to the surface, hiding
the firescale underneath.

Lee Einer


#8

It sounds as though you are getting firescale. Are the grey
ghosts really purplish in coloration? What I have been told is
to make up a batch of Pripps Flux and coat the pieces with it
prior to soldering. The is available in the archives
but if you can’t find the recipe, contact me off line and I will
send you the “recipe” I was given by one of the very helpful
folks on line here at Orchid. Shael dakotahdog@msn.com


#9

Sharron: yes as someone said its firescale, or oxidized copper.
The best way to get rid of it is to prevent it. Go to the Orchid
archives and do a search on Pripps Flux. This is something
easily made yourself and you spray it on the silver first by
warming the silver with your torch. When you spray it on the warm
metal it coats the piece to protect it during soldering. Its not
100% perfect but it will keep oxygen away from the piece during
most soldering…Dave


#10

Sharron - You are running into the bane of jewelers - firescale.
When copper is heated in the presence of Oxygen, it forms
cuprous oxide - CuO -a black layer which quickly dissolves in
pickle, and cupric oxide - CuO2- a purplish compound that forms
within the metal - your culprit. Tim McCreight’s Complete
Metalsmith suggests a number of practices to prevent its
formation (avoid prolonged heating - the longer and hotter you
heat your work, the deeper the firescale will go; use enough
flux - flux absorbs the oxygen, etc.) and a couple of remedies
to repair it - bright dipping in a 50/50 solution of nitric acid
and water at room temp. ( wear gloves, protective clothing, and
a respirator) rinse and scratchbrush and repeat until scale is
gone, then neutralize with baking soda and polish and finish. Or
electroplate over the scale, or depletion gild. Best of luck.

Mike


#11
also possible to heat, pickle and quench the piece multiple
times to bring  a layer of fine silver to the surface, hiding
the firescale underneath. 

Hey Sharron, The Fine silver only conceals the firescale for a
short time & then it resurfaces. Seems to me to be the better
part of wisdom to make up a Prips solution & use it on your
piece first, than trying to fight firescale after. I have a
brooch which I tried to grind the firescale off of, it has a
huge hole in it’s middle section. I keep it hanging in my shop
to remind me I don’t need to go there again (overheating my
metal) if I pay attention. Good luck, and I will send good
soldering thoughts you way. Helene


#12

Hello Sharron - (btw - I really admire people who write concise
answers . . . here is my wordy one!) In my many hours of removing
firescale - (although I do use preventative measures!) - I
discovered a way to remove specific “islands” of firescale very
effectively. By using a flexible shaft brush - with medium or
stiff bristles - and say, bobbing compound - and by turning the
piece at the appropriate angle to catch the light and be able to
see the splotches of firescale - I could carefully go for it and
remove just those areas with the brush.

It may sound rather inefficient to go back and forth from the
polishing machine to the flex shaft - but I think it saves time
in the long run and definitely saves polishing away too much of
the metal. Besides, the walk is “exercise”. Depending what the
situation is - I will sometimes keep an extra fine sharpie pen
at the polishing site and circle the specific areas remaining of
firescale - so, when I lose my place by walking to flexible
shaft or when coming back to it later - it saves time in
relocating the areas of firescale to remove. Really works well -
and I use this method for larger forged pieces as well as smaller
pieces with textured surfaces that I don’t want to disturb. Oh, be
sure and use a face mask when using the flexible shaft for this
type of polishing - don’t breathe the dirt. A bit messy to use
polishing compound at the bench - but I find this system for
removal works well. I love Tim McCreight’s verbal description of
firescale - something like ##*~! Cynthia


#13

I remember melting and fusing copper wire to form gaskets for
sealing vacuum system flanges years ago . I used oxygen and
hydrogen in a torch. After fusing it was my practice to slowly
play the hydrogen flame with no oxygen all over the copper which
had been heated to reduce the copper oxide formed and slowly cool
the piece down to where the oxide was very much reduced or
eliminated. Does anyone use H2 and O2 torch enough to have
noticed whether the fire scale on soldered items can be
eliminated this way? The problem comes about because Silver at
high temperature transmits oxygen thru it at a very high rate
(compared withthe diffusion of most other substances) and thus
will oxidize the copper in sterling at a fairly good depth in the
body of the piece So the copper may not have to diffuse to the
surface completely to form the black copper oxide of fire scale.
Other methods of reducing the oxide or to remove it with acid
may be possible. Will dilute (5% or so) muriatic acid remove it,
as opposed to pickling with the standard sulphates? Jack T.