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Firescale/Firestain - was Strange casting results


#1
The top or first layer is black and is called cupric oxide.  The
layer that is typically under that layer is reddish and is called
cuperous oxide.  It is this red layer that is called "fire scale". 

Speaking of which … has anyone ever deciphered Oppi Untracht’s
descriptions of “firescale” and “firestain” ("Jewelry Concepts &
Technology, p. 416-417)? As I read it, his definition of “fire
scale” includes both cupric and cuprous oxide, with the primary
distinction being how deep the layer of scale goes.

That’s fine and good except that his definition of “firestain"
sounds exactly like what he has already defined as the deeper of the
two layers of “firescale” in the section above. And nowhere does he
give the chemical makeup of what he calls “firestain” as opposed to
"firescale.” Furthermore, everything he says about "firestain"
applies to what I’ve always considered to be “firescale,” i.e.,
cuprous oxide.

Are these two sections just poorly written or are there actually two
kinds of “firescale” as distinct from “firestain”? I tend to think
it’s the former (no disrespect intended – it’s an amazing book).

Beth


#2
   Speaking of which ... has anyone ever deciphered Oppi
Untracht's descriptions of "firescale" and "firestain" 

don’t overanalize it by looking at chemistry. Look instead at the
metal.

firescale is the visible black oxide coating left after heating.

Pickle the metal and the firescale is gone, leaving a nice matte
white surface.

Polish that surface and discover the whitish/reddish odd color in
the silver which, if you polish deep enough, gives way to the clearer
more silvery clean metal underneath. That smudgy layer is fire
stain.

The distinction is clear when you consider the difference to be
visual and practical, rather than chemical. Chemically, they’re not
quite so distinct, since each has a bit of both types of oxide.
Amounts differ, of course, and the structure is different too, with
fire scale being a layer of nothing but oxide that sits on the
surface, formed of copper oxides that have migrated out of the
surface layers of the silver. Fire stain, by contrast, refers to
the remaining oxides that are still imbedded within the silver’s
surface layers.

Peter


#3

Peter, your description of fire stain and firescale confused me. I
always though cuprous oxide, that purple stain, you get on soldered
or cast sterling was called firescale (or many other words that are
not used in public). I had never heard the word firestain.

I did a search on the web on the word firescale and firestain. It
appears that that a majority of the articles use firescale or
firestain to describe the purple stain. There are several articles
that use firescale to describe the black oxide.

I guess it again proves that there are no standards in our art. Lee
Epperson


#4

Hi Peter,

  Don't overanalize it by looking at chemistry.  Look instead at
the metal. 

And I thought I worded my post so carefully that no one would try to
tell me what firescale and firestain are . I really do
know for all practical and chemical purposes what the differences
are; and I really did want to know if Oppi Untracht was talking
about a third type of oxide since he describes two kinds of
"firescale" and then goes on to describe “firestain” as if it’s
something different. Oh well. As I said in my original post, either
those sections are poorly written or he knows something we don’t!

Thanks anyway,
Beth