Silly question but how Is boric acid different from borax? Leonid
you have answered my questions about how the metal reacts to being
melted, I'm sure it is a very complex process that I stand little
chance of controlling.
Process may be complex, but as goldsmiths we do not have to
understand down to molecular level. Flux is an integral component of
melting, so it make sense to spend some time discussing it.
For melting silver neither borax, nor boric acid are suited.
Adequate flux is sal ammoniac. The best flux has to have additional
components, based on particular circumstances. Generally, the
dirtier the metal, the more complex flux recipe should be.
There are 3 main enemies standing between goldsmith and sound ingot.
They are - oxygen, flux acidity, and common impurities like iron. Sal
ammoniac, at high temperatures will decompose into ammonia and
hydrogen chloride, both powerful oxidizing agents. They will form
oxides that will rise to the surface. Also by-product of reactions is
free oxygen. Use too little and not all of the contaminants will be
removed; too much will result in free oxygen been present, which is
detrimental for silver. Oxygen can be converted to carbon dioxide by
introducing carbon, which is accomplished by addition of flour.
Oxydes has to be contained in some kind of a medium. Borax can be
used for this purpose, but regular soda is far superior. Soda also
neutralizes acidity of flux. It acidity is not neutralized, some of
metal can be trapped inside molten flux, a condition some of you
Iron will be present, no matter what you do! Working metal with
magnet only reduces amount of iron.Complete elimination should be
done in crucible by adding potassium carbonate. One more component
to finish the recipe is powdered glass.
Presence of glass makes flux to retreat to back end of crucible
during pouring. That way one get ingot without flux been trapped in.
Needless to say that working with chemicals is dangerous and can
cause serious injury. Good ventilation is a must.