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
firescale is the visible black oxide coating left after heating.
Pickle the metal and the firescale is gone, leaving a nice matte
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
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