Black Gold

Jewelry Discussion
1

Fellow Orchidites! I have a technical question to pose you all.

Does anyone know of a good formula for Black Gold?

Traditionally the only alternative was from oxidization. Hydro
Tetrachloride giving the richest, deepest black. But this means has
proven to be too carcinogenic.

I have heard of an traditional Ethiopian goldsmiths technique of
alloying a black gold. An example of which can be seen on the
www.yvel.co.il site.

Any suggestions?

Thanks. Kim Lilot. From Sunny San Francisco (Finally!)

2 
  Fellow Orchidites! I have a technical question to pose you all.
Does anyone know of a good formula for Black Gold? Traditionally
the only alternative was from oxidization. Hydro Tetrachloride
giving the richest, deepest black. But this means has proven to be
too carcinogenic.

So far as I know, and I’ve been looking too, all the folks
selling/producing “black gold” are using a surface coloration, not a
true alloy color. Some are more durable than others. The most
durable I know of (I think) is a silicon nitride coating. It is, I
think, a vapor deposition deposit (though I’m not sure) and for
durability over most metals, is a multi step process requireing
several under coats of different materials to provide a secure
attachment to metal, as a direct coating straight on the gold isn’t
well compatible, and it comes off. Rado watchs use it on some of
their cases and watchbands. It’s an extremely hard material which
resists abrasion, damage, scratching, etc. very well. It can also be
manufactured as a solid material, such as tube sections, which can be
incorporated into jewelry, but as it’s a hard brittle material, not
malleable or ductile, one has to carefully consider how it’s used.
Rado (again) also uses the solid machined material in some of their
products. Machining is only possible with diamond tools, as it is
the equal of carbides (or harder), in hardness, I’m told.

The above, by the way, also applies to blue golds, that have also
been described and sold now and then. They’re surface colors, either
patinas or actual coatings. The sole real exception to this that I
know of is the aluminum/gold alloys which produce a lovely
purple/violet color. This is also a brittle material that can be
shaped only really by grinding, same as a lapidary material, though
it can be soldered, and I’d expect, welded (laser?).

Now, if anyone knows that I’m wrong, and can point me to a true
black gold formula, PLEASE do so. My boss is just itching to find
such a thing too, and I’d get major brownie points were someone to
point me in such a direction with success…

cheers

Peter Rowe

3

Thanks Peter, I have always been keenly interested in the Rado watch
finish. It is virtually impossible to learn any facts about cutting
edge technology because of its’ proprietary nature. Ron @ Mills
Gem, Los Osos, CA.

4

At this years Santa Fe Symposium Valerio Faccenda gave a paper
titled “Advanced Technology for Jewelry Industry” in it he talks
about three ways of producing a Black Gold . Unfortunately none of
them is a bulk coloring of the gold. All three are surface coatings;
one is an electroplated coating of ruthenium or rhodium with
blackening agents. the second is a controlled oxidation process on
a gold cobalt and chromium alloy (Au 750-Co 150-Cr 100) with the
comment that the alloy is not “easy” for investment casting, and
finally a plasma assisted chemical vapor deposition technique of a
hydrogenated amorphous carbon developed by a Swiss company called
Bloesch. The process is called Blaktop and it is cited as the
technique used for the Rado watches. Most of the paper is devoted to
testing the surfaces for wear resistance and some oh the
coating process. It is published in the 2002 proceedings of the
Santa Fe Symposium which is available from Rio Grande

Jim
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160

@James_Binnion
Member of the Better Business Bureau

5

Hi Peter, I once had part of a gold pendant “plasma sprayed” with a
black metallic oxide (I forget what it was exactly), along with some
experimental rings. The coating, and it was just a coating, not
actually “black gold”, was virtually indestructable and would not
wear off. The process was very much like air brushing, in that a
fine metallic powder was sprayed onto the surface using a torch-like
sprayer, whose flame both heated the surface and melted the metal
powder prior to it hitting the surface. A large number of metallic
powders were available, I believe even gold, and I had it done by a
gentleman who had a specailty machine shop. He primarily used the
process to build up bearing surfaces that could not otherwise be
repaired or replaced, and then re-machined them. I never pursued it
any further, but if you were looking for a way to create a permant
black color (or other color, depending on the metal used), this was
certainly effective.

Best regards,
John

6 
   Thanks Peter, I have always been keenly interested in the Rado
watch finish. It is virtually impossible to learn any facts about
cutting edge technology because of its' proprietary nature.

How true. If you want to play with some of the stuff, you might try
contacting Lee Marshall at Bonny Doon. They had some sections of
ring sized tubing of the stuff that they were using the press to
“set”, by expanding silver tube placed inside it, with the
anticlastic methods their press is so good at. Gave a band ring with
silver liner and edges, with this black inlay. He probably knows
where/how to get more of the stuff.

Peter

7

My standard source for patents relating to gold is the Gold
Bulletin, a scientific journal put out by the World Gold Council .
They used to have a section in every journal giving abstracts of new
patents, including ones used in jewelry production. A more recent
companion journal geared to the jewelry trade is Gold Technology.

I ran a quick search on black gold (www.gold.org) but failed to come
up with anything. I know I’ve seen a technical article on black gold
somewhere (I was an avid collector of colored gold alloys), but
can’t locate it. Perhaps I was dreaming? Will keep looking…

Janet in Jerusalem

8

Hi Folks,

I see it wasn’t clear from my last post that www.gold.org is the url
= ofthe World Gold Council, the body which publishes both journals
mentioned (the Gold Bulletin and Gold Technology).

Janet in Jerusalem

9

Hi All, Found this reference to Black Gold on the web.

“The color of gold is determined by which chemicals it is found with
or which metals it is alloyed with. Black gold from Brazil gets its
color from the chemicals found with it. Alloying with malachite gives
gold a black or near-black purple color.”

From:

http://comspark.com/chronicles/gold.shtml

Steve
San Diego

10

Hello all, I have checked the archives and have found very little
info on “Black Gold”, so I come to you all for any you
might have. In my readings, some have said that there is no such
thing, while others say that it can be bought (at Argen among other
places). I have also read that black gold is alloyed with Iron and/or
cobalt, silver and copper. Does anyone know if Black Gold can be
cast? Any info please!

Cheers from Bali.
Marcus Terrey

11 
  "Black Gold"... some have said that there is no such thing, while
others say that it can be bought (at Argen among other places).

We just purchased a bit of Argen’s 18K black gold to try out. As
supplied, it’s a yellow color typical of 18K gold. It consists of
75%gold and 25%cobalt. It seems to work about the same as other
yellow golds, maybe a bit stiffer, but no real problems. The color,
of course, is yellow, not black. You get the black as a fairly
durable and tenacious surface oxide when you heat the gold in air to
around 1500 F (I forget the exact temp, but it’s a nice bright glow,
so forget treating it after you’ve set stones). The literature I
had didn’t mention casting, but I’d assume you could cast it, so long
as you used a machine capable of properly covering the metal during
melting and pouring with an inert or otherwise oxygen free gas shield.
I’d rather hoped to be able to color it chemically, rather than with
heat, to allow doing setting of colored stones and diamonds in it
before coloring, but Argen says the heat treat is the only way, (I
might play with anodizing anyway, since they may not have considered
that) Plus, they implied that it worked best only the first time.
Not sure why that might be. Their literature called the heat treat
step “degassing”, which sounds like what dental techs do with cast
crowns prior to applying porcelain, in order to keep it from
bubbling. It’s a heat treat in vacuum, rather than what’s done here.

And that’s all I know 'bout it.
Peter

12

Marcus,
All types of “Black Gold” are surface effects. In other words the
bulk metal is not black, the surface of it is turned black through
some process. The Argen black gold is an surface oxidation there are
some other types that rely on electro plating or CVD (chemical vapor
deposition) to produce a black coating. The Argen metal can be cast
but must be cast in an inert gas shielded casting machine.

Jim

13

I happen to be in the alloy biz. There is no commercially available
black gold alloy suitable for ordinary use as we see it. There are
many ways to get the surface to be black, and that is what we see
with the odd artisan style exception. On several occasions folks have
brought black gold rings for analysis and found it was a coating
(black rhodium, plasma coating, whatever) I may call Argen to see
about the report…

Allow a alloy guy a short rant if you will… Every uncommon color of
gold is uncommon for very good reasons, like the brittleness of blue
and purple if you can get it at all. If these odd colors were
reasonably available and or well behaved as casting or fabricating
gold, you would see them in showcases all over the world.

I bet one guy the cost of the “black gold” ring from Italy that it
was just a coating. I took a graver and cut right through the coating
revealing the white gold underneath. Boy was he disappointed.

Daniel Ballard
Precious Metals West