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Exotic alloys


#1

Hello! Does anyone know of a source for the more exotic gold alloys,
such as blue or purple gold. I know they are difficult to work
with, but I have a design that screams for blue gold accents.

I have never made my own alloys before and would rather buy them if
possible.

If there are no commercial sources, does anyone know where I can
find instructions for making this alloy? Remember I am new to
alloying metal.

Thanks!
Andrea L. McLester
Tampa, FL USA
http://almclester.netfirms.com


#2
   If there are no commercial sources, does anyone know where I
can find instructions for making this alloy?  Remember I am new to
alloying metal. 

Without special equipment (induction or electric melt furnace able
to pull a vacuum on the metal or shield it with inert gas), you can’t
practially make purple gold. It’s an 18K alloy of gold and aluminum.
Melting it in the presence of oxygen, even traces, destroys the
aluminum, and you get a lump of very porous and useless scrap for the
refining bin. Remember too, that this alloy behaves more like a
lapidary material once you made it. It’s hard and very brittle, more
like glass than metal. You can’t work it other than grinding it to
shape and polishing it, and soldering to it (use a good active,
probably fluoride flux) It’s properly called an “intermetallic”, not
actually an alloy, as it doesn’t have the normal crystal structure
associated with our normal jewelry metals. But it is a lovely
violet/purple color.

Blue golds I’m aware of are actually a steel grey color as their
actual metal color. The blue is a surface oxide, or patina, not the
actual color of the alloy. I don’t know the formula. All modern
references to it I’ve seen treat the alloy, and the coloring process
for it, as proprietary trade secrets of the producers. Older books
tell of a gold/iron alloy, in several karat qualities, referred to as
blue gold. The color is darker grey than white golds, and the
references I’ve seen were to such alloys as used in multicolored
victorian goldwork. I’d assume that they call this blue in the same
way they call a high silver/gold, or silver/cadmium/gold, alloy,
green. They’re still yellow, but compared to standard yellow golds,
they appear more greenish. compared to standard white golds, a dark
steely grey might seem more blueish, even if it isn’t. And a bit of
heat color on it might well be actually blue, though again it’s just a
surface oxide. I’ve never tried that, so don’t know how well it
works, but can attest that a torch melted sample of the gold/iron
alloy (in any of several karats) produced a rather nasty cracky
material usable only for small accent decorations, not for anything
needing any structural strength. This may well have been due to the
primative melting methods I used, though. Just a torch with a
standard crucible.

Hope that helps.
Peter Rowe


#3

This site is more to specific and easier to read:

http://www.2globalvillage.com/aaj/042001.htm#feature

Guy…


#4
    Hello! Does anyone know of a source for the more exotic gold
alloys, such as blue or purple gold.  I know they are difficult to
work with, but I have a design that screams for blue gold accents.  

In the March or April issue of Lapidary Journal there is an article
about alloys and various noble metals and it just so happens that the
colors you are looking for were mentioned. I must warn you though,
according to the article these colors are custom alloyed and are not
fabrication/casting friendly (hard and brittle). I will try to pin
point the article so you won’t have to go hunting.

Tom
Arizona USA


#5

Sounds like a great opportunity to add to your skill pool :smiley:

I searched the list and it’s been posted before here is a post from
1999.

http://www.ganoksin.com/orchid/archive/9906/msg00050.htm

Hope it helps,
Guy…


#6

A question for Peter Rowe,

Your posting on the Exotic Alloys is most interesting.

In the Japanese technique of pouring molten metal through water into
a cloth cradle in the water, the billet sits in the cradle and
hisses, burps and whistles as it solidifies and gives up the oxygen
the metal absorbed during melting. Question… What do you think
might happen with a gold/aluminum alloy cast this way?

What is the ratio of 18K gold to aluminum?

Bill in Vista


#7

Bill,

The japanese technique prevents the metal from just sitting in air
as it solidifies, absorbing more oxygen. With many alloys, oxygen
absorbtion is not significant during melting as the flame protects
it. But the only oxygen or gas thats given off while the solidifying
metal is under water, is gas that’s merely dissolved, like CO2 in soda
pop. It doesn’t affect any oxygen that has chemically combined with,
for example, copper, to form copper oxides. Copper containing alloys
cast this way will have less oxides in them than those just poured
into an open air mold, but they’ll still have the same oxides in
them from any oxygen absorbed during melting or pouring, until the
metal reached the water. it’s better, but not perfect. The water
bath (actually for the metal, a steam bath) is also a controlled
cooling rate which can be beneficial for a uniform crystal structure.

46irst, the 18K purple gold alloy is 18K gold, which is 75% gold,
and 25% aluminum. It’s NOT a mix of 18K gold with aluminum.
Technically, the perfect mix is more like 22 percent aluminum, but
that’s not a big difference with a strict 18K proportion, and doesn’t
affect the color.

As to the japanese method of pouring ingots, I expect it might help
some, but I doubt it would help enough. i’ve not tried it. When I
did try to make this alloy, using a torch, I couldn’t even get the
alloy to melt clearly enough to pour. Just the attempt to melt the
two metals together formed, as they combined, a progressively cruddy
gunky mass, not a pourable liquid. Remember that aluminum has far
more of an afinity for oxygen than does copper or precious metals,
and the oxygen it finds combines with it chemically to form an
oxide, it’s not just absorbed, free to be expelled upon cooling. I
expect (but don’t know for certain) that even only partial oxidation
of the aluminum in the mix would prevent the proper formation of the
ordered array structure that gives the exotic purple color. so far
as I know, all the folks I’ve heard of who’ve made this stuff with
good results have melted the mix under truely oxygen free conditions,
such as induction or electric melt furnaces with inert gas shield, or
under vaccuum. Note I say melted, not just the ingot mold, which is
what the japanese method really is. I don’t think a torch is capable
of doing it. Hydrogen fuel, maybe, but again, I’ve not tried it in
many years, so I’m not really sure of that. On the other hand, I do
recall having little difficulty melting just aluminum itself, which
is of course a much lower temperature, in graphite crucibles in a gas
melting furnace, for varous casting projects. Excess oxidation didn’t
get in the way with that. It’s always possible that something
similar might work. But for my part, I have my doubts. Try it,
please. I’d love to find I’m wrong. 20

I’ll mention at this point one other reference to purple gold some
may find of interest. In the 70s, I bought a small paperback book on
various patinas and the like which mentioned this alloy, by a
metalsmith/teacher who’s name I’ve long forgotton, as well as the
book itself, which has long disappeared. What he’d done was to raise
holloware vessels in sheet aluminum, and gold electroplate them.
Then he’d fire them in a kiln, watching them carefully until the gold
just started to dissipate into the aluminum surface. Times right,
he could pull the piece from the heat at just the point where the
gold incorporated a suffient amount of aluminum to form that purple
gold color. Too much, and the gold was gone, too little, and of
course there was just the gold color still. an interesting concept,
but again, not one I’ve tried. I don’t recall the temps he was
using, but expect it to be perhaps in the 600 - 800 range, perhaps?
Just a wild guess…

Peter