using scrap silver

On Fri, 05 Jan 2007 04:18:45 +0000, Abrasha wrote:

Abrasha schrieb:
Andy Dingley wrote:
Abrasha wrote:

The only way to get a good silver ingot, is to protect the melt with a
reducing flame to keep the oxygen away, and pour the melt through a
reducing gas flame that burns over the ingot mold, again to prevent
oxygen from entering the melt. Setups like this are usually not found
in small goldsmith's shops, but only in refineries.
How about in a hamfisted blacksmith's workshop? 8-)

We're melting silver in a propane-fired kiln / forge / furnace /
carelessly made insulated tin box. It's not too difficult to control
the atmosphere to be reducing. Would you regard this as an adequate
substitute? Would you reckon it worthwhile to try and do the pour
inside this atmosphere too, or is it enough to merely melt the
crucible-full in there, then quickly take it out and pour it in the
open air?


I would try to pour in that atmosphere too, because as soon as you get
the melt into the open air, it will suck up oxygen like there is no
tomorrow.

You cannot possibly be fast enough to prevent oxygen from entering the
melt. The only way to prevent this is to provide a reducing atmosphere.

BTW, I found something online: http://tinyurl.com/ybwcyr and
http://tinyurl.com/yc3xdn (read under Historical)

Molten alloys with Gold and/or Silver are sucking also Hydrogen in ascender.
H-atoms much more than H2 molecules.
This H-atoms are produced within the light blue area of a strong reducing
flame. This is the area between the yellow part and the violet-blue part.
So porosity can be increase enormously if the flame is too long and the
distance to the metal is too short.
We have better results with a flame which is adjusted in th optimum of oxygen
and gas or air and gas and taking a distance of minimum 1 cm between the spit
of bright blue part of the flame and the surface of the metal.
So only the violet-blue part of the flame (the chemical reaction in the plasma
is finished here) should blow to the fluid metal.

With best regards,
Heinrich Butschal

Kendall Davies wrote:
Are there any special precautions I should take when melting and re-using
scrap silver ready for the rolling mill and draw plate?

I intend to use clean offcuts, and some old work that has not sold.

Regards -Kendall
After yo done your melting it seems the oxides and the impurities rise
to the surface of the ingot! So file or sandpaper the outer skin and the
rolling comes perfect! Also prior to melting dip all the scraps in
boiling sulphuric acid to get rid of superficial impurities and check
for other materials other than silver! Then prior to melting dip the
scraps in a solution of boric acid an water. Heat up slowly to build up
a protective flux coating and be soft with the flame!