Heather Coleman wrote:


Now this brings me on to my questions...

While making the final rings I annealed the metal very often to soften
it... sometimes I quenched it in acid while it was still very hot and
the metal surface when beaten on the stake was very silver coloured, not
gold at all (?!)

It is NEVER a good idea to quench hot metal, and especially very hot
metal, directly in acid. Always quench in water and then pickle (remove
fire scale) in acid. Or quench in denatured alcohol.

Other times I quenched it in acid when it was much cooler and the
surface was a pale golden colour.

The final colour of the rings (because the last time I annealed them I
did not quench but left the very black oxide on them) is a deep rich
gold/copper colour which is rather nice.

I assume, that you did remove the fire scale in the acid.


Am I right in saying that this is because the gold still has a lot of
copper in it and the copper oxides are trapped in the structure of the
gold?

No. Every time you remove the fire scale in the acid solution, the acid
removes a bit of the copper from the surface layer of the metal. The
result is, that this will change the color of your alloy.

If you started with a yellow gold alloy, the final color will be paler.
If you started with a red gold alloy, the final color will be more
towards fine gold (a richer yellow).

Yellow gold alloys have more silver and less copper, and red gold alloys
have more copper and less silver. Since in pickling some copper is
removed and gold and silver stay behind, the yellow gold alloys get
paler, the red gold alloys get richer yellow. All of this works much
better with 18K gold alloys.

If you watch the video on my web site (it's a 20 minute video), you'll
see that at the end of the video (from around 15'12" to about 16') I
turn the lights of and work in the dark. I do this so I can easily see
the color of the gold change while I am heating it with my torch to a
dull red. I then let the piece cool to black, at which point I quench
the piece in concentrated hydrochloric acid (DO NOT DO THIS AT HOME!!!)
I repeat this process about 4 to 6 times, and each time in between I
brush the piece with a brass brush to polish the thin layer of fine gold
that has formed on the surface. This process can only be performed with
red gold alloys that contain a large amount of copper and very little
silver. The process is called "depletion gilding". Because it is
"depleted" of copper.


When I quenched in acid from VERY hot (the glow only just died away) the
colour went almost completely silver which was what puzzled me the
most...

That probably means that your alloy contained a large amount of silver
and very little copper. A yellow gold alloy. Since the copper was
depleted, the godly and silver stay behind, and the silver makes the
alloy look very pale.

I assume this is because the gold crystalised at it's surface
due to rapid cooling and so it was reflecting the light in the surface
layers?

No, see above. Crystallization has nothing to do with it. You are
removing copper.


And I assume that if I wanted to change the colour back to the best gold
that I can achieve with this overworked material I would have to reheat
and quench them at a much lower temperature?

No. You have to file or sand the entire piece to remove the layer you
have created at the surface, to get back to the original alloy.


Finally, this is a really daft question to ask but is this how different
coloured golds like red and white etc. are created?

See above. In general the more copper in the alloys, the redder the
alloy will be. The more silver, the paler (yellower) the alloy will be.
If you have gold and silver only, you can get a "green" gold. If you
alloy with small quantities of nickel of palladium, you get "white"
gold. If you alloy with Aluminum, you get a unworkable very brittle,
purple gold.

Here are a few sites that explain gold color a bit further:
http://www.gold.org/jewellery/technology/alloys/
http://jewelry.about.com/cs/goldbuyi...old_alloys.htm
http://tinyurl.com/9xc9v


In conclusion... those two original rings have certainly been through
the fires,

Almost every piece of jewelry on the planet today contains some gold
that has "been through the fires", because through the ages, only a
rather small amount of gold has been mined, which has been recycled over
and over again. And almost all of it is still around. Gold is so rare
that all the gold ever mined could fit into a cube measuring just 20
yards on each side.

Abrasha
http://www.abrasha.com