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Iron meteorites and gold

This is well known in the electronics industry, and well
documented. Google "solder bond." I have had such micrographs in
the past, done by our met lab to analyze failures. 

Soldering and brazing both involve diffusion but with the exception
of very specialized type of brazing there is a significant amount of
solder or braze alloy that remains in/on the joint. Full diffusion
of the braze or solder alloy requires a significant amount of time
and a very tiny amount of braze alloy to begin with, diffusion is
slow. To diffuse to the point of where there is no braze alloy left
in the joint typically takes hours.

James Binnion

He will not because it is a fantasy. Diffusion brazing does occur
but requires very special prep and tiny amounts of the alloy. 

All true, except the fantasy part.

Leonid Surpin
www.studioarete.com

With white gold alloys, I can often see a slightly different colour
on the joint after soldering - is that the solder left behind as a
filler, or a modified alloy in the area of the joint? 

I hope you do not mind if I pass the chance of commenting of use of
lead solder. It simply does not interest me, in any way. About your
question on white gold soldering, let me answer it the following way.

When was taught to work with platinum - platinum solders were not
available in Russia, so we use fine silver to solder it. Joint
visibility was never a problem, because joints were carefully
prepared, and neither was the hallmarking.

Leonid Surpin
www.studioarete.com

When the hard solder penetrates into the metal to be joined this
is actually a weld, is it not? 

It can be looked at that way.

I always try to find answers in history of a technique. The art of
joining metal with fire started with blacksmith began soldering with
copper. Iron was brought to red head and copper was introduced into
the joint. Copper was not used as filler. It actually diffused into
the joint. The method fall out favor with blacksmiths, after forge
welding was discovered.

Goldsmiths perfected this technique by using alloy instead of copper
to lower required temperature. So, from that perspective, it can be
called welding.

The confusion arises because modern welding fills the joint with
welding alloy. Someone lowered the temperature of that alloy and we
have brazing. To me distinction always was in function of joining
agent ( whatever name one want to use ) In one case we have diffusion
bond, and in another case we have joint filled with other substance.

It has very important differences in practice. Soldered joint cannot
be unsoldered. If someone teaches you to unsolder, you are taught
brazing, not soldering. It may look like a shortcomings, but
technique of soldering allows one to do many soldering in small area,
without worrying about previously soldered joints. The purest form of
soldering is granulation.

Leonid Surpin
www.studioarete.com

“Real” is what exists even if we do not believe it in…all else is
conjecture.

As to molecular bonds in metal…I thought all metals were
crystalline in nature, not molecular…I believe it has to do with
weather or not the bonds between atoms are covalent (between two or
more atoms in a set arrangement) or metallic in nature in which
there is a shared electron cloud among the atoms which allows for
things like forging hot and cold.

I have recently obtained a metallographic microscope and will soon
have a Tukon micro hardness tester. I would be happy to have a look
at one of your brazed bonds when I am set up to do so. If I had a
way to sample the chemistry of the joint interface and the base
metals I would do that as well…maybe through the university.

Over the years I have been quite stunned by the actual study of
things rather than relying on blacksmiths have told me is happening.

I guess in the end it does not really matter to a craftsman if he is
doing one thing while thinking it is another…provided the
technique does its job I see no possible damage. There are great
problems which develop however when we teach without knowing as that
propagates misunderstandings and false truth.

I know many knife makers who can make a great blade, but have no
idea as to what really occurs upon quenching other than the steel
gets hard…nor can they describe a solid phase forge-weld and yet
they make beautiful pattern-welded work.

We live in a time now that such things can be known and even tested
in our own shops…with some equipment designed for that. The tests I
have seen show:

the base metal…a diffusion bond with new alloy…solder or braze
metal…diffusion bond with new alloy…base metal. So there you have
five metals and four interfaces all may have different properties
and will show under a cross-sectional metallographic examination. I
would think if the bonded area were held at temperature X for a time
X (both vary) then the diffusion would increase to a point where
there may be only base metal/interface/base metal, but this may be
an undesirable bond…hard to say without specifics. Extremely thin
(several atoms thick) solder joints can do this in “normal” time I
would think, but again…just conjecture.

Ric
Sturgeon Bay, WI
www.doorcountyforgeworks.com

Duh, it appears that we are no closer to clarifying a long standing
misunderstanding of the terms ‘fire stain’ and ‘fire scale’ than we
were before, with all due respect to James and others who have tried
to clearly describe these terms.

If one reads Charles Lewton Brain’s article available in the
archives, it indicates that the terms are interchangeable though one
apparently refers to the Cu20 (cuprous oxide) which has a reddish
color and the other to Cu0 (cupric oxide) which is black. He goes on
to explain that the black cupric oxide does not just affect the
surface of the metal but it penetrates deep inside the metal as well.
(Note: There are very good pictures in the Orchid Archives of
’firescale’ which shows it penetrating well over 10 microns into the
surface of the metal.)

From Charles Lewton Brain’s article in the archives;

'....Firescale or firestain is a reddish purple toned bloom or
stain that appears on silver/copper alloys such as sterling
silver when they are heated in the presence of oxygen. It even
occurs in gold alloys with high copper contents. As it generally
appears in the form of blotchy patches following abrasive
polishing, it is seen as a blemish which destroys the clear
reflectivity of finished silver surfaces. It is usually observed
best when the silver object is placed on a piece of white paper.
Sometimes it is chosen as a surface finish in order to emphasize
texture as when a silversmith like Lois Betteridge uses firescale
to accentuate the visual depth of the hammer marks on a surface
by polishing off the tops of the resulting texture leaving them a
lighter gray than the reddish tones of the firescale in the
recesses. 

Firescale is caused by oxygen combining with copper present in
the silver-copper alloy. A sterling silver alloy contains 925
parts out of a thousand parts silver, and 75 parts out of a
thousand parts copper. When the alloy is exposed to oxygen in the
air at higher temperatures during annealing or soldering
procedures, the copper at the surface is converted to Cu2O
(cuprous oxide) which has a reddish color, then to cupric oxide
CuO which is black. It is, however, not just the metal at the
very surface that is affected but deep inside the metal as well.
Silver has the ability to absorb oxygen at high temperatures and
conduct the oxygen to the interior of the metal itself where it
can bond with copper atoms present thus causing deep firescale to
occur."..... 

In Mark Grimwade’s excellent book ‘Introduction to Precious Metals’,
on page 95, he also combines the two terms but then goes on to
explain the difference between the black Cupric oxide as it appears
on the surface of the metal while the Cuprous oxide is a sub-scale of
reddish gray! He then describes the pickling process to remove the
surface oxide layer (cupric oxide) but that the cuprous oxide
sub-scale will remain and be revealed as a fire stain layer!!

If we are now saying that ‘firescale’ is easily removed by pickle,
we are not quite correct. In fact, the surface oxides of 'firescale’
are removed by pickle but the portion that has penetrated the surface
is not removed by pickle. To remove that portion of ‘firescale’ one
must bombe it with hot nitric acid (not at all recommended) or
sand/grind/polish it away.

In other words, while we are aware there are two different actions
taking place, there is no clear definition as to which term is which.
Perhaps the term is not the important thing but understanding the
process is.

I have always referred to ‘fire scale’ as the hard purplish/grayish
sub-scale described by Grimwade, while the reddish stain on the
surface I believe is ‘fire stain’ and is easily removed with a swipe
of the finger or a brushing with a brass brush and soap as
lubrication.

At the risk of being wrong, and for want of a better definition, I
will continue to refer to the reddish stain on the metals surface as
’fire stain’ (Cuprous oxide) and the hard purplish/grayish sub-scale
as ‘fire scale’ (Cupric oxide).

I know many knife makers who can make a great blade, but have no
idea as to what really occurs upon quenching other than the steel
gets hard...nor can they describe a solid phase forge-weld and yet
they make beautiful pattern-welded work. 

I have a very pronounced slavic accent, when I speak. Once, I
purchased a course on accent correction, but I quickly realize that,
if every time I need to say something, I have to think, where to
stick my tongue and how to twist my lips, I would not be able to
speak at all.

In manual arts, it is the same situation. We love to engage in
high-minding discussions about diffusion bonds and etc…, but does
the understanding of the processes, from science point view actually
relevant? I do not think so. In the final analysis, it is what you
can do, rather than what you can explain, or formulate, or describe.

I can teach soldering by launching into long winded explanation about
solidus and liquids, or I can simply say - watch for the rounding. I
can write out a thermo-dynamic equation, modeling the temperature
equilibrium, or I can say - turn you cheek slightly, so you can feel
the heat. Human senses are far more superior than any instruments.
All one need to do is to learn to use them.

Leonid Surpin
www.studioarete.com

Duh, it appears that we are no closer to clarifying a long
standing misunderstanding of the terms 'fire stain' and 'fire
scale' than we were before, with all due respect to James and
others who have tried to clearly describe these terms. 

The problem is that there are no universally accepted definitions
for either term, many seem to use them interchangeably. My
understanding is the fire stain (as in stained, cannot be easily
cleaned) is the subsurface oxide and fire scale is the "scaly"
red/black surface oxide that can be easily removed. But both are
imprecise terms to refer to the cuprous and cupric oxides whose
descriptions you quoted from Grimwade and Lewton Brain. I doubt we
will come to a consensus on this.

James Binnion
James Binnion Metal Arts

As to molecular bonds in metal..I thought all metals were
crystalline in nature, not molecular...I believe it has to do with
weather or not the bonds between atoms are covalent (between two
or more atoms in a set arrangement) or metallic in nature in which
there is a shared electron cloud among the atoms which allows for
things like forging hot and cold. 

Not sure what you mean by molecular bonding, there are 4 forms of
atomic bond Metallic, Ionic, Covalent, and van der Waals. Bonds
between non metals are typically covalent and between metals and non
metals they are typically ionic and of course between metals it is a
metallic bond.

James Binnion
James Binnion Metal Arts

In other words, while we are aware there are two different actions
taking place, there is no clear definition as to which term is
which. Perhaps the term is not the important thing but
understanding the process is. 

I am going to give very simple solution to firescale problem, and
fancy fluxes is not it. The solution is do what french silversmiths
do. Silver, hallmarked according to french standard is 95% silver.
Not every french silver object was done by that standard, but the
fact that some were, should trigger some thinking.

In any silver alloy, with less than 95% silver, the copper phase is
going to separate approaching 900 degrees. And that makes it
available to react with oxygen. A few pennies of increase in cost of
material, will save you a lot of trouble.

Leonid Surpin
www.studioarete.com

Hi Guys,

I doubt we will come to a consensus on this. 

Being a blacksmith, I come across fire scale, and it’s a really hard
crust that can in some instance be picked of, but in most it has to
be ground off.

I first came across the term “fire stain” when I was soldering
sterling silver, and it was due to the copper.

I keep the terms separated by disipline, “fire scale” blacksmithing,
“fire stain” jewellery.

It’s only my view.

We may never come to a consensus (we don’t even spell words the same
way), but I wont rule it out :wink:

Regards Charles A.

...we are not quite correct. In fact, the surface oxides of
'firescale' [on silver/copper alloys] are removed by pickle but the
portion that has penetrated the surface is not removed by pickle.
To remove that portion of 'firescale' one must bombe it with hot
nitric acid (not at all recommended) or sand/grind/polish it away. 

I repeat my earlier suggestion, that occasionally bright-dipping the
silver/copper item in dilute nitric acid (no need for it to be hot)
or in a mixture of PhDown and hydrogen peroxide (takes longer) may
get rid of the red cuprous oxide. I have to deal with this all the
time, when soldering/brazing/reticulating brass, which is generally
85% copper and cannot be heated without the red oxide appearing (the
black cupric oxide indeed easily comes off with pickling in PhDown
alone). I never have problems with any kind of “scale” – I’d love
to hear someone who works with silver say that they have tried
bright-dipping and they still got the firescale when finishing their
jewelry piece.

Judy Bjorkman

I repeat my earlier suggestion, that occasionally bright-dipping
the silver/copper item in dilute nitric acid (no need for it to be
hot) or in a mixture of PhDown and hydrogen peroxide (takes longer)
may get rid of the red cuprous oxide. 

While this works to remove surface oxides it will not remove the
fire stain which is actually deep in the metal matrix not just on the
surface. If you use a strong enough nitric solution and keep the
work in the acid long enough you can remove fire stain but this
involves literally etching the whole surface away till getting beyond
the fire stain. Brass and copper do not get fire stain they just get
surface oxides which are easily treated by the solutions you
recommend.

James Binnion
James Binnion Metal Arts

Judy,

I'd love to hear someone who works with silver say that they have
tried bright-dipping and they still got the firescale when
finishing their jewelry piece. 

your bright dip methods, as you say useful with brass, don’t work
for fire STAIN, which is the name used for the penetrating red oxides
of copper that are found under the layer of black oxides. A bright
dip will remove oxides from the surface, yes, but so would ordinary
pickle. The problem is that, unlike what you deal with in brass, the
red oxides penetrate into the metal, sometimes to a significant
distance. Bright dipping removes it from the outer surface, but the
acids cannot affect what’s under the surface.

Again, fire scale is not the same as fire stain. Close relatives,
but the first, the black surface oxides, are easily removed by
pickling, without even needing peroxide. The reddish oxide of copper
is almost impossible to remove without removing the whole layer it’s
in, silver and all, simply because you cannot reach it chemically.
It’s in the metal, not on it. This happens because with silver, when
heated, oxygen is able to not only react with the surface, but it
penetrates into the silver, and can oxidize copper that’s within the
crystal structure near the surface too. That shows up as a sort of
"creamy" slightly pinkish toned shadow on the metal when you polish,
usually only easily visible when you get to the rouge stage, where if
you’ve cut through that layer in some places with the buff, and not
in others, it creates a really blotchy look. Bright dipping helps
slightly, but then you have to repolish, and the problem reappears,
because the acid couldn’t get below the actual surface. You can use a
more aggressive bright dip, an actual etch, to remove enough of the
surface to get below the fire stain, but this is difficult to
control, and still leaves you with a surface that then needs a good
deal of polishing.

The main solutions to fire stain are either to plan on completely
removing all of it with aggressive buffing, which can be destructive
to good work), or by carefully preserving that layer intact, so the
whole surface is that color. Or better, proper use of anti fire stain
fluxes, like Prips flux or Cupronil, prevent it’s formation in the
first place, which is much easier than dealing with it. Or the
easiest modern solution, the use of different silver alloys, like
Argentium, which simply don’t form this subsurface oxide layer. Fire
stain problems were the entire driving force behind the development
of Argentium and similar alloys. If fire stain were as easy to deal
with as a simple bright dip, nobody would ever have bothered to
develop Aregntium.

Your peroxide pickle, by the way, is not fixing your brass by
removing red oxides of copper, it’s removing an actual surface layer
of metallic copper. The red color is because your heating has removed
the zinc from the surface layer of brass, leaving a slightly
porous/dull copper rich film, which is then reddish. If you pickled
it, the copper oxides on the surface were removed, but that red
copper layer stays. The peroxide enhanced pickle gets that copper
layer off, so you’re then back to the brass color. This is not the
same as fire stain. Perhaps the references to it as being caused by
the red oxides of copper are confusing. That’s true, but fire stain
is diffuse enough in the silver that the color is not actually red.
More a faintly warm or pinkish creamy colored shadow, distinct from
the clearer, brighter, darker polish you get on clean sterling
silver.

And yes, back to your “I’d love to” statement. I did try all sorts
of acids and bright dips at one point, long ago, just to see, since
Oppi Untracht also mentions bright dipping as a possible solution.
but I never got anything that approached a good result unless I let
the acid dissolve enough of the silver to actually get all the way
through the whole layer, copper oxide and silver both. That wasn’t a
good solution at all.

Peter

Charles Anderson, blacksmith, offered:

Being a blacksmith, I come across fire scale, and it's a really
hard crust that can in some instance be picked of, but in most it
has to be ground off. I first came across the term "fire stain"
when I was soldering sterling silver, and it was due to the copper.
I keep the terms separated by disipline, "fire scale"
blacksmithing, "fire stain" jewellery. It's only my view.

A view that makes complete sense to me, taking into account the
difference between what happens to Ag and to Fe when they both get
hot. Iron scale (" the thin film which forms on the surface of
wrought iron in the process of forging. It consists essentially of
the magnetic oxide of iron, Fe3O4." ) is very hard and doesn’t come
off easily, and does look and act like a scale, a distinctly
different layer of material than what it’s on top of, that can behave
like a skin or scale that flakes and chips to some degree. Not fun to
deal with, and since iron and steel are mostly worked in oxidizing
atmoshpeheres, hard to avoid. it will dull files and laugh at
anything but aggressive sanding or grinding.

Dar
sheltech.net