Hello Ed, Melting old gold is not difficult but can be frustrating.
First separate the gold parts with no solder in it, by cutting solder
parts of. This good quality gold can directly melted with some borax
and sugar. Do not overheat this gold and use a reducing flame
(overdose gas), it will give direct a good alloy back. Cast this gold
of in a sheet form or sand, or Delft clay. Hammer this on the sides ,
anneal, and quench in alcohol (after dull red). a few times before you
can start rolling.
The rest, gold fillings, dust, solder and other sjit can be used for
casting which does not need to be of a good quality. Or it can be made
in a workable alloy. I hope you have not mixed all kind karats so that
you do not know at which alloy you will end. Start by cleaning on steel
particles by stirring it with a magnet. For casting gold, just melt
with a lot of borax and cast something out of this scrap gold.
For a usable ductile alloy it needs to undergo some more
purification. First you have to remove the steel particles with a
magnet. If you are not sure, boil your lemel in sulphuric acid to
remove all steel. Than melt the gold and stir special melting powder
trough the melt, to takes out the first amount of dirt and to binds
some of the wrong alloys. (This powder is the cheep special melting
powder,that the normal suppliers have). For the next step I use Auro
Purifax for cleaning. This Auropurifax is a special gold cleaning
powder, It absorbs the wrong alloys and removes dirt. Just stir it
trough the melt in amount of 5 to 30% depending on the dirt. You will
get a wonderful ductile alloy back which does not crack during
rolling. But if it does so, do the above trick again. Also adding some
zinc will help in making it ductile. And if this does not work, send it
away for refining, or cast something out of it.
If you want to know more, just mail to me.