alloy compositions

[goldenchild]

Can anyone tell me a typical 10k yellow gold alloy composition? I have a chain that I had xrf'd so that I could make a matching custom pendant. Both readings for each element were different by a few percentages. I'm guessing because it was calibrated for very high karat gold of course. I went ahead and got the average of the two readings and came up with 17% silver 38% copper 5% zinc and 40% gold. Not plumb but we already know this is usually the case.

After alloying the metals it was pink. A very light pink. The yellow almost showed through depending on the angle it was held in the light. I tried even adding a little more gold but it was still pink. So I decided to refine it and start over. I added silver to the alloy to inquart and I wish I would have weighed it. What resulted was the best looking cornflake I've ever made and it was almost the exact hue of gold I wanted. If I would have just added a little more silver and it came out a little more pale it would have been perfect but no longer 10k.

So anyway. I've scoured the internet looking for typical 10k yellow gold alloy compositions and the numbers are all over the place. Based on this experience I think the best formula I found was 41.7% Au, 33% Ag and 25% Cu. I'm looking for a paler yellow. If I have time later I will post a picture of the chain for reference. Thanks in advance for any help.

 

[nickvc]

Most low karat alloys are really a copper alloy with gold in them.
9 k yellow is in English alloys 10% Ag 37.5% Au 7% Zn 45.5% Cu.
If you increase the gold content to 41.6% I'd be tempted just to drop 2%off the silver and the balance off the copper, many imported goods here have little or no silver in the low karat alloys.

 

[goldenchild]

Interesting. So is it the zinc that is offsetting the pink hue created by the copper? I've read that zinc is a "decolorizer". But to which metal? With an even higher Cu content than I was using I would think that you'd get an even more pink to red hue. What could have happened in my melt to cause the pink hue?

 

[nickvc]

Possibly overheating the alloy and burning the base metals out. When you melt just get it molten give it a good stir or swirl in the pot and allow to cool or pour direct into cold water. Try polishing the metal and see what colour it actually will finish up been.

 

[4metals]

One trick alloy manufacturers use to prevent evcessive zinc loss is to mix zinc and copper together and melt into a grain, this is added to the molten silver and gold and results in less zinc burning off.

 

[goldenchild]

So I did some melting tonight and successfully created the 10k alloy I was after. I thought of a plan to test combinations of alloys using 1 gram of pure gold as the .417 percentage for each sample. Working with quantities that small in not fun.

I first tried the combination nickvc suggested. After filing it a bit I still got a pink gold (left button second picture). It is the ratio I found most while researching but maybe I was doing something wrong while melting. So then I tried the .417 - .33 - .25 combo and success. After filing a nice yellow like I was looking for.

Interestingly enough there was a silver film on the ingot after it was done like what happened here
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=7315.
Kind of like what happened here This is what happened the first time I created the pink alloy. A reddish film on the ingot. I suppose the predominant base metal comes out most. Anyway after giving it a little bit of filing action the nice yellow appeared.

Thank you nickvc and 4metals for your help.

Copper alloy on left

 

[Harold_V]

Kind of like what happened here This is what happened the first time I created the pink alloy. A reddish film on the ingot. I suppose the predominant base metal comes out most.

Not exactly. What you witnessed is the oxide of copper, often referenced as *fire coat*. Pickling in sulfuric acid (or Sparex) is used to eliminate the oxide coat, revealing the color of the alloy within.

When working with alloys of gold, remember that copper shifts color towards red, and silver shifts color towards green.

Harold

 

[goldenchild]

So here is the final product. Since the piece was so simple it was actually rolled and cut out instead of cast. I wish I had remembered to take a picture of when I first sanded it. Now that I have all the equipment I will be casting my own pieces. Video coming soon...

 

[samuel-a]

Nice work man.
Clean and simple!

 

[goldenchild]

So here is my very first cast piece. Enjoy.

[youtube]http://www.youtube.com/watch?v=ddBgrOQw8GM[/youtube]

http://www.youtube.com/watch?v=ddBgrOQw8GM

 

[goldsilverpro]

Very good, goldenchild!!

 

[philddreamer]

Bravo, Mario, Bravo! 8)

Phil

 

[Harold_V]

As you may know, I spent over twenty years working with manufacturing jewelers, refining their waste materials. I'd like to pass on a tip to you, one based on an actual experience I had with one of them.

This particular customer brought one of his clients to my place to ask me some questions about alloying. Seems he had made a ring (white gold) for the customer, which had globules of what appeared to be nickel in the shank. It was obvious the metal had not alloyed upon melting. The ending of this story is not good. It cost my customer a client, who had implied that it was done intentionally, to deceive.

When you melt, don't rely on the torch to stir the metal. Only induction melting will assure that the metal is a homogeneous mix. Melt the pure gold, which is inert, first. When it is molten, add the base metal and stir well, using a carbon rod.

Aside from that little ordeal, what I witnessed was very good!

Well done.

Harold

 

[goldenchild]

Thanks all for the positive comments and advice.

 

[Dr. Poe]

Very good Harold. True alloys are made by melting the highest melting point first, then dissolving the other metals into it.
Bronze was discovered when to molten copper tin was added.
Looking at the silvery film on the button above, I perceive that rhodium (which hates to alloy with gold) is floating atop. the density being only 12sg. Other PGM's would either alloy or sink to the bottom. The indentation reveals that this is on the top. Dr. Poe

 

[qst42know]

Nice ring Goldenchild.

Are you in your jeweler friend's shop or did you invest in a bunch of equipment?

 

[kuma]

So here is my very first cast piece. Enjoy.

Goldenchild , very nice work indeed chief! 8)
Thanks for sharing! :mrgreen:
All the best and kind regards ,
Chris

 

[goldenchild]

Thank you qst42know and kuma. This is my lab/shop. It's where I do 100% of my work. I own the oven and vacuum.