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Question about Melting Gold - Changing Colours during annealing

Hi :-)

I was chatting on this group back in November 20th of 2004 about working with gold and have another question that someone might know something about and want to comment on.

I will have to explain my story in order for someone to get the idea of what I have been up to... I am no professional so bear with me! :-)

About 4 years back I took two of my hall-marked gold rings of what I believed to be 18ct gold and melted them in a crucible in my pottery kiln at about 1300 deg Cent... I knew nothing at the time about working with gold and so assumed I would get a blob of gold that I could experiment with as back then I could not afford to buy new.

Well... if I had used a flux it would have helped but my crucible broke and I ended up with several scattered blobs of good looking gold and a load of very nice rich coloured red and black glassy material where I assumed the copper part from the gold had merged with the glaze that was on my homemade crucible!

Next thing I decided to do (still at that time with little knowledge) was take the dozen or so bits of broken crucible out into my garden and blow torch them until the metallic gold ran off them. I scattered some flux on to help them run and eventually after a long time I managed to salvage a blob of gold from the mess I had created.

I think after that I had a go at beating the blob into a disc which worked and then the project got left for another year or so.

When I decided to finally do something with this blob I re-melted it AGAIN in a small pure porcelain (unglazed) crucible that I made with some flux and then beat it into a ring... this time I managed to create it into a small doughnut shape that I beat on a ring making stake and I almost got it to a ring that I could wear but because I did not keep annealing it often enough it split...

So the gold went back and got remelted yet again!

Last week, I decided to have another go :-) and this time I took the blob and reformed it as a little doughnut (blob with a hole in the middle) and this time I managed to form a single ring which I later sliced down the middle and made two beautiful narrow rings from. The appearance is very rugged with beat marks all over and is exactly what I wanted to achieve.

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 (?!) 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.

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?

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... 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?

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?

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

In conclusion... those two original rings have certainly been through the fires, I have learned a few things the hard way, but I now have two lovely rings that I should enjoy for a few more years to come.

regards Heather

Reply to
Heather Coleman
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[That would mostly be the flux, with perhaps a little color from the metal oxides.]
[Quenching in acid will create toxic fumes, and can splash corrosive fluid around. Steel tools anywhere in the vicinity can experience accellerated rusting. Most jewelers use a milder pickle solution based on sodium bisulphate ("Sparex" is one brand - it's also sold as swimming pool Ph adjuster), which works almost as well with fewer bad effects.]
[The acid quenching may have been depleting the copper at the surface.]
[Not the oxides, but the metal itself.]
[I don't know; I've never done that.]
[That seems to have worked...]

[No, that's done by alloying with different metals.]
[At least you didn't hurt yourself; that's the important thing. If you do this again, use a torch, not your pottery kiln, and a real crucible. Flux is good, but don't use too much - it's meant to cover the gold during melting, but is just in the way during pouring, and it can make inclusions if it gets mixed into the metal. Ingots are inherently rather porous, use a purpose-made jeweler's ingot mold to get the best ones you can. Anneal by heating to cherry red and quenching immediately; with high-karat gold you don't need to use acid or even pickle - water will do.]

Andrew Werby

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Reply to
Andrew Werby

You probably could have welded that split back together, if you have a small torch flame.

I don't know anything about this acid quenching, and my little amount of gold work is in the area of reclaiming and refining gold as pure as I can. But, a very small amount of some metals can turn the gold to a pretty white color. Most of the contaminating base metals can be removed with acids when it is cool. But, then, maybe you don't want to remove all the base metal for jewelry.

Jon

Reply to
Jon Elson

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.

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

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.

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.

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

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.

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:

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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

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Reply to
Abrasha

No, that is not possible. the only way to remove "base metals" (whatever you mean by that), is to send the alloy to a refiner, or go through the trouble of refining yourself, which is a rather arduous process if you want to do it yourself.

Abrasha

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Reply to
Abrasha

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