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Any information on firestain (really any at all)


#1

I would like to know about the most annoying thing about working with silver. We all know it. We all hate it. Firestain. Principally I would like to know how to best prevent. Is it with flux or with an alloy and what that flux or alloy would that be. I also have a few questions about it in general which I will list here:

  • does it go away when you reuse scrap? i.e you have some firestained sheet, melt it and roll some new sheet would that sheet have all the firestain from the old sheet plus all the new firestain from being Annealed

  • How can I remove it without destroying detail?

Additionally, I have decided to alloy sterling using yellow/cartridge brass (70Cu30Zn) and from what I can tell it seems only a smidgen softer than standard sterling and very ductile. It also seems to firescale less but isn’t immune to it, does that sound right?

I will eventually switch to a palladium sterling such as continuum but right now I’d like one that is the same (or similar at least) in price to sterling. No more than a dollar a gram :slight_smile:

Anyway thanks for any help

ArgentumMoon


#2

Hi,
There are many posts on this subject in the archives that offer advice, and here are a few thoughts from myself.

clean the metal so that the flux is able to maintain full coverage

use an anti-firescale barrier flux to protect the metal
(heat metal, apply prips flux, prips flux will dry to a white coating upon contact with the heated metal)
(then apply flow flux only to the area to be soldered)

anti-firescale barrier flux achieves different results than fluxes formulated to wet/clean/flow solder

the barrier flux will take up the surface oxides into the flux solution, until exhausted

(I get best results with Prips flux…sometimes incorrectly spelled Pripps flux in some posts…it has an added ingredient that extends the ability of the flux to absorb copper oxides)

do not heat the metal too hot, and/or too long…

(the flame contains oxygen, so get in and get out, to reduce the amount of time for oxygen exposure to the metal, and to complete the operation before exhausting the barrier flux)

some alloys contain ingredients, such as germanium, which will sacrifice itself to the oxygen, before the copper can interact with the oxygen,or something of that nature…

Julie


#3

Hi again,

actually…a good way to approach this question is to research and answer these questions…
I have done, and have a good general understanding, but probably am not the best person to try to spell it all out in its technical glory!

what is firescale? (surface)
what is firestain? (subsurface)
what causes the firescale and firestain?
how do you avoid firescale and fire stain?
how to control heat/ temp from torch onto metal?
what are the best products to prevent firescale and firestain?
what are the best soldering/ annealing/ heating blocks/ materials/ surfaces to help prevent firescale and firestain?
why and how do these products work?
how do you best use these products?

Julie


#4

I apologize if this sounds mean (?), but you really must learn to start searching our Archives… This topic has been discussed in great detail many times. You will find a great deal of valuable information there. One of the great advantages of using the archives is that you will hear from many very knowledgeable and very experienced Orchidians who no longer read Orchid. It’s really good general advice to everyone to check the archives before asking questions. Nine times out of ten your questions will be answered there…:-)…

Julie has just provided above a good list of firestain questions to start with, all of which have been answered extensively in the archives. After digesting all that has been written already, you will undoubtedly be in a position to ask some really good new questions…:-)…!

Janet in Jerusalem


#5

Get yourself a big bottle of Cupronil and a we small spray bottle.Warm the metal and keep it hot as you spray a nice white even coat. I have been using it for 20 yrs. and no firestain. Of course there is nothing you can use if you overheat the piece to stop it.


#6

I have searched the archives and found information on fluxes and alloys, I was wondering what people’s opinions are today. Actually I stumbled across a post of yours wondering about s88 and s57na from united precious metals. I too have been considering (quite seriously) s88. How did you find that alloy, no firestain? Worked the same as sterling? Decently hard?

If not, have you used fluxes such as cuprinil, how effective is it?


#7

You need to learn how to use the search function…:-)…

Here are hundreds of archive entries on ‘flux’ from the Orchid search engine:
https://orchid.ganoksin.com/search?q=Flux

And here are hundreds of entries on ‘alloys’ from the Orchid search engine:
https://orchid.ganoksin.com/search?q=alloys&expanded=true

A google search of ‘flux’ limited to the Ganoksin site came up with 1,960 results:
https://www.google.com/search?q=site:orchid.ganoksin.com+flux

A google search of ‘alloys’ limited to the Ganoksin site came up with 1,820 results:
https://www.google.com/search?ei=_Rq2XOOPOoKmwQK0-YXYDA&q=site%3Aorchid.ganoksin.com+alloys&oq=site%3Aorchid.ganoksin.com+alloys&gs_l=psy-ab.12...166734.169060..172324...0.0..0.151.804.0j6…0…1…gws-wiz…0i71.TOXNxwicy_4

You can of course narrow the search to get answers to your particular questions.

Have fun!

Janet in Jerusalem

PS If the links don’t work for you, just do the search.
PPS By the way you’ll find hundreds of entries just on Cupronil (if you spell it correctly…).


#8

From searching the archives, it seems that by using prips flus and not overheating my sterling firestain can be pretty much eliminated? Or must I use an alloy such as argentium, continuum or s88 to prevent such firestain?


#9

Hi,

Here is a copy/paste of a reply post by Peter Rowe.

This is a great post and he explains alot about firescale/ firestain and fluxes

This is the post where I learned about what the different properties of the ingredients in the Pripps flux. (heat range, surface tension, etc)

peterrowe
Nov '11

(question from poster)
I have questions about firescale. Is it possible to prevent it? Is
it really possible to get rid of it once it happens? this also is
probably something at the molecular level.

(reply from Peter Rowe)
Sally, go through the Orchid archives looking for posts on the
subject of Prips flux (sometimes misspelled Pripps).

Fire scale is fairly simple to deal with, since it’s a surface oxide
that comes right off in the pickle. The real problem is fire STAIN,
which is that pinkish/greyish “shadow” that shows up on the silver
just as you’re getting to a final polish.

The conjecture that it’s “something at the molecular level” suggests
you don’t fully understand how this happens.

On heating sterling silver, oxygen in the air becomes able to
diffuse somewhat into the silver surface, and to oxidize the copper
in the silver. The copper within the silver is also somewhat mobile
when the metal is hot. Copper oxides too can migrate some, and that
which reaches the surface oxidizes further (the black oxide of copper
rather than the red). It’s then trapped at the surface. That means
there’s something of a one way street going on, and with some
sustained heating and continued exposure to oxygen, you end up with
a four layered surface. At the top is the black copper oxide. Then is
a layer from which the copper is mostly gone, since it was close
enough to the surface that it reached the surface and did not return,
so this zone is then almost pure silver. Below that is a zone where
oxygen reached, forming the red oxide of silver, but here, it did not
manage to migrate (diffuse) out of that layer, being too deep to make
it out. This is the layer that gives you the fire stain problem.
Below it, of course, is the depth to which oxygen did not reach, so
there are no more oxides, and it’s clean silver. When you take this
metal after heating and pickle it, the surface black oxide layer is
removed, leaving you with a matte white surface. it’s the fine silver
layer. If, when you polish the end piece, you don’t cut through this
layer, then you’ll not have a problem with the finish, but it can be
thin, so this is difficult. If you polish into the fire stained
layer, then it contrasts with the fine silver layer, and even more,
with the un oxidized sterling silver below it.

The solution to all this trouble is simple in theory. You simply
have to prevent oxygen from reaching the surface of the metal while
you’re heating it to solder or anneal. The answer is the right type
of fluxing agent.

With gold, a simple coating of boric acid, left by a slurry of
alcohol and boric acid powder into which the metal is dipped, is
enough. But gold doesn’t form the fire stain layer, so it’s less of a
problem anyway, since simple pickling gets you back to clean metal.

With silver, it’s a bit more complex. plain boric acid is also the
fluxing agent most effective at blocking atmospheric oxygen from
reaching the surface, but though some jewelers will use the above
simple boric acid/alcohol dip by itself, boric acid alone is not
fully effective since the surface tension of the silver can prevent
the boric acid from properly coating the silver. And the boric acid
doesn’t, by itself, fully cover the whole temperature range you wish
to protect the silver through. Mixing borax with the boric acid
solves that temperature range proglem. Mixing in other wetting agents
allows the flux to properly cover the metal. Prips flux uses
trisodium phosphate (TSP) to do this. There are other commercial
fluxes, such as cupronil, or firescoff, that also are effective at
protecting the silver during heating. Note that many soldering
fluxes by themselves, are not totally effective. The highly active
white paste fluxes, such as Handy flux or Dandix, for example, do not
seem to properly block oxygen from the metal, even though they are
dissolving oxides from the surface. So with them, even with the flux,
fire stain can sometimes form. The less active Prips flux or
similarly acting fluxes, do not do this.

If you learn to properly apply and use Prips flux (which you make
yourself. Its very cheap. Using it takes a little practice, as it’s
best used by spraying it on, not just brushing), your problems with
fire stain, and fire scale, will be gone. When I first learned silver
work back in the 70s, in an undergraduate metals course, Fred Fenster
taught us to use Prips flux, with the same statement, that it would
never be a problem. And he’s been right, at least for me. The only
times I get fire stain in fabrication, is when I’ve been too lazy to
use the Prips. Casting is another issue, though. Here, fluxing isn’t
something you can do to prevent fire scale or fire stain on the
castings. There are other ways that help, but the simplest is to use
one of the newer fire stain free casting silver alloys.

Peter Rowe


#10

I use propane flame. But cover the holes of the burner with a movable ring. This makes the flame oxigen-poor. Very little problem with firestone this way.
Another thing is never quench your piece in pickle. That makes the problem worse. It etches the copper out of the surface of the metal and leaves a layer of fine silver, but creates more firestone underneath.
Always quench in water first.


#11

Quenching in pickle creates neither fire stain nor fire scale. I always quench in pickle and have neither.

Janet in Jerusalem


#12

Perhaps it should be stated not to put silver into a pickle with steel of iron tongs. There is some alchemy that goes on between the silver and the iron and the pickle that creates scale of one type or another. A nightmare to clean off, maybe not a nightmare but certainly more work than you need to do.

Use copper or wooden tongs.

Don Meixner


#13

Hello, I’m not an expert in jewelry making but here is some information I have experimented with that seems to work on fire scale on sterling silver.

This is some of the stuff I think we are talking about.

I make a salt water solution 4 parts water and one part salt. I put a copper conductor on one side of my beaker and a copper conductor on the other side. The negative side(left side) is on your part side(Ring) with a hook on it to hang your part or ring.Not sure if the part side needs to be copper but it works. The positive side is on the right side with just a copper piece of metal.

If you reverse your connectors you put more firescale on your part.

You can use a 1.5 volt battery but it takes longer. I used an adjustable rectifier an apllied 3 volts. It takes about 1 1/2 minutes.

1.5 volts applied will take longer.

I did not use any preventitive measure like boric acid or and alcohol or cuprinoll prior to soldering. I did not pickel it after my soldering . I did try to polish it with a yellow Rio cloth which just shined up the fire scale.

So I let it fizzle in my salt water bath at 3 volts for 1.5 minutes.

When I pull it up it looks like this.

When I wipe it off with with just a paper towel, it looks like this.

When I buff it up with Rio’s yellow cloth it looks like this. Didn’t have to use any sand paper.

I put it to a buffing wheel.

I put it back into my salt water bath with the terminals reversed after I had polished up and it puts the fire scale back on it.


#14

Thanks, I was wondering how quenching in pickle would cause firescale or stain. I always quench in pickle, which still might be a bad idea for health concerns. Got it in my eye once, that was not a fun afternoon…


#15

Hi,

I believe it is safer(?) to quench in water, then put item in pickle. so that you don’t get splattered with pickle.

Julie