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Roberts-austin alloy


#1

Hello everybody! I�m a novice in the goldsmithing wonderworld and am
dying to solve one great mistery that has been puzzling my curiosity:
Does anybody know something about the roberts-austin alloy (purple
gold, 79Au, 21Al)? How fragile is it? How do you generate it? I�m
thrilled by the prospect of the purple color, hope it�s not just an
illusion! Go create, Emanuele


#2

The purple is indeed pretty. But the compound is not properly an
alloy, but what is called an intermetallic compound. It is
completely non-malleable and non-ductile, meaning it is very
brittle. Treat it as you would a lapidary material (stone), with the
exception that you can solder to it, unlike stone. So far as my
limited experience with it goes, making it will require atmosphere
controlled melting aparatus, to exclude oxygen during melting.
People I know who’ve made it used induction melting equipment under
vacuum, but I’d assume an inert gas shield would work too. My own
attempts with a torch melt were not successful, but maybe someone
using different fluxes has had sucess. I don’t know. Although the
stuff is only usful as an ornamentla inlay or similar use, it is
nevertheless a pretty color, and unlike the so-called blue golds and
a number of similar exotic colors that are surface patinas, in this
case the purple/violet color is indeed the color of the material.

One old little pamphlet I’ve got somewhere described on interesting
variation of the stuff, whereby aluminum was used to create an object
(in this case, a holloware vase), and it was then gold plated. This
was then fired briefly in a kiln, just enough so the gold started to
dissipate into the aluminum, forming this coumpound at the surface.
It was removed from the kiln as soon as the color started to form,
after which the color remained stable at room temps.

I never tried that, but it sounded interesting. Wish I could
remember the name and author of the pamphlet/paperbound book.

Peter


#3
     My own attempts with a torch melt were not successful, but
maybe someone using different fluxes has had success. 

Peter, If you find yourself in a mood to experiment, and have some
24k just lying around, try mixing up some purple gold without using
an induction melting apparatus. Roll the 24k into foil and wrap it
tightly around the aluminum. Use a good bit of flux and melt the
packet. Here’s the tricky part: just as the aluminum starts to melt,
pour sugar on top of the melt! The sugar will instantly melt, and
carbonize. When the stuff starts to cool, just fish your lump of
purple gold out of the sticky black mess and “voila!”…a lump of
purple gold!

Now, you just have to carve it into something usable...and clean

your crucible!

Sounds simple, right? Sure it does! Unfortunately, if you wait too

long to pour the sugar, you will have a lump of black gold. Pour too
early, and you will have 24k with purple spots/stripes. But if you
get it right, this can cause metalliferous insanity!

Douglas Zaruba