Temperature question - Alloying down to 14 karat from fine gold, silver & copper

Jewelry Discussion
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Hey guys!

New with casting gold here, and my question is how your workflow would look like when you wanna alloy and cast your own 14 karat gold.

When I search online i see that the best casting temp for 14 karat Yellow gold will be around 900 - 1000 celcius, depending on Centrifugal / Vaccum, size of casting, thickness etc etc etc.

However, now I stand with three fine metals I wanna alloy together with different flow & casting temps.

Fine gold

  • Melting Point - 1064 degrees C. / 1945 degrees F.
  • Casting range - 1160 to 1170 degrees C. / 2120 to 2138 degrees F.

Fine silver

  • Melting Point - 962 degrees C./ 1762 degrees F.
  • Casting range – 1050 to 1060 degrees C./ 1922 to 1940 degrees F.

Copper

  • Melting Point - 1085 degrees C. / 1985 degrees F.
  • Casting range 1150 to 1180 degress C. / 2102 - 2156 degrees F.

So say I wanna mix these 58.5 % + 20.75 % + 20.75 %…

  1. Can I then reach the temp of the metal with highest flow temp, throw all my metals in, and then take down the temp to correct casting temp for 14 karat? Does the metals have the properties of alloyed 14 karat metal in molten form? or

  2. Do I have to cast the metals at temps for 24 karat gold, and get the metal to solidify on ingot or charcoal, and then recast again with my new 14 karat alloyed metal?

Best regard William

2

Welcome to Orchid.

Melt the copper first, then add the gold, then add the silver.

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Hey Betty. Thank you!

Gotcha, but my real question is if I can then take the molten mixture down from 1085 celcius (Copper melting temp) to 975 Celcius (example 14 karat casting temp) without any trouble of any of the metals solidifying or giving me any other troubles?

best regards william

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I think you’re not getting many answers because few people add alloy this way. What you’re doing is more to satisfy your curiosity than anything else? Excellent, proven premixed alloys are available and inexpensive so that’s what nearly all use. It does make sense to buy 24K and alloy as needed if your gold requirements are unpredictable. That way you’re not stuck with as much unused prealloyed gold, if you say bought 14K yellow and found you need 18K white. But few mix their own alloy in order to karat their fine gold, it’s quicker to buy it.

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Hey Mpandfamily! Thanks for your reply.

Alright I get your point, and it is indeed very convenient. But my impression seems a bit different since the only two jewelry tools / metal suppliers near me in Denmark dosent sell any premixed alloys containing gold.

When you buy already premixed alloys, then you’re bound to use the colour of metal that the manufaturer sells I guess?

I can imagine sometimes if i want my own unique rose / green / yellow, then I want to be able to control the ratio of gold/silver/copper/zinc myself, therefore I would need to know this basic metalurgy to do so!

Best regards William

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That makes perfect sense William. I’m in the US and buy them from United Precious Metals in New York. You’re right, you are sort of locked-in to their colors if you do it this way. In my case that consistency is an advantage because I’m confident all my colors will match thru time. Someone who might help you is the head metallurgist at Stuller, his name is Shan Aithal, he has been very generous with answering this sort of questions. You can connect with him on Stullers forum, benchjeweler.com I think. I hope that helps!

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Thanks Mark. Will follow your lead and see if i can get a hold of Shan!

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Hey William,
I looked into the phase diagram for your specific 14KY alloy.
It shows a liquidus of approx. 855C or 1570F.
Your alloy composition is very unique and will result in a very pale yellow (with a green hue), which is not a preferred color here in US.
In addition, your composition lacks any kind of deoxidizer, like zinc, which is normally added (1) to protect the copper from getting oxidized during the melting and (2) form a smoother casting surface.
Zinc additions significantly alter the yellow color of the 14K gold as well!

With regards to melting - surprisingly, you will find that once you melt silver (which is the lowest melting metal of the three) and start adding copper and gold chunks, they go into solution (dissolve) easily!
It is not necessary to use a very high melting temperature (like that of copper) to blend the 3 metals.
The mantra for any melting operation is to use the lowest permissible temperature with very good melt surface protection using boric oxide flux.
Zinc addition will further reduce the starting starting melt temperature.
I would assume a typical casting temperature for your blend would be around 1000C - higher for light pieces with smaller gates and lower for very large pieces with heavier gates.

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Hey Shan, thank you so much for joining the conversation! Just popped you private message earlier via Stullers forum, so never mind answering that!

All the information, it is GOLD! Got a heads up in a private message earlier about the terms eutectic point & phase diagrams, so I am currently looking into this!

Great info about the oxidizers aswell, will look this up. Saw some casting services offering colours without zinc aswell, so dident think it was crucial… However seems like 85 % of the time zinc is involved, and a smoother casting surface sounds amazing.

Also great to hear about permissible temperature. Have heard about the 4 basic casting temp ranges, where you wanna hit it just right in order to reduce shrinkage porosity as it cools down to its solidification temperature

If you got time for 2 quick ones.

  1. Any rule of thumb of ratio / precautions when adding zinc to the mixture? I see some use up to 0.25 - 7.25 %

  2. I melt in an electric melting furnance - says no flux is nessescary when melting… Long been wondering if a pinch of boric oxide flux would help my melting process anyway?

Best regards William

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Good morning William (at least it is here in Lafayette, Louisiana)!

Any rule of thumb of ratio / precautions when adding zinc to the mixture? I see some use up to 0.25 - 7.25 %

Zinc Ratio:

Unfortunately, there is no rule of thumb for amount of zinc additions to yellow gold alloys.

In Europe, it is common to use as little zinc as possible and in US, we use a lot more zinc.

The amount of zinc added (coupled with copper and silver additions) is to control the yellow color.

Unfortunately, the color designation used in Europe, like, 1N, 2N,…5N is with 18KY golds.

I don’t have any information of tying these color designations with 14KY gold formulas!

Generally, 18KY golds have lower amounts of zinc than 14KY golds.

Zinc is not typically added to red/rose/pink gold alloys because it bleaches out the red color.

Precautions:

Zinc is not added late in the melting sequence because it has a tendency to flare up and get oxidized.

It is usually added first because it melts and facilitates dissolution of other high melting metals like Cu, Ag and Au!

I melt in an electric melting furnace - says no flux is necessary when melting… Long been wondering if a pinch of boric oxide flux would help my melting process anyway?

Are you using the furnace to mix the metals only or are you using it for casting as well?

Flux is recommended during melting process for physical protection (zinc will do the chemical protection)from oxidation; flux is not recommended during casting
process because when flux gets in between melt and investment, it forms defects!

I apologize for my wordy response!

Regards,

Shan

Shan Aithal, Ph.D

Corporate Metallurgist

Ext 3615

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Good morning, a bit ahead of time over here he he!

Dont apologize for the wordy reply, im just taking all the knowledge in, its awesome!

Alright cool, makes good sense! To get a general idea of the ratio of metals, colours & karats, im benchmarking a bit with the visuals provided by Carrera casting! Finding this usefull.

And yes, I guess it’s all about taste, and it seems that EU likes the yellow a bit more pale and in US more deeper yellow ?

In theory, could there be added a Zinc dimension to the phase map since it also plays a part in the colouration of the final cast? But then again, it would be the same case with nickel, platinium etc.

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Precautions - Noted, thanks a lot.

If you have any handy bookmarked links for the color designations even though its only 18 karat, I would love to see them!

I use for both mixing & casting ! Then I assume i would leave the boric oxide flux out if it messes with the mold, and instead add some zinc for colour properties, smoother surface& oxidation prevention!

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Best regards William

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I searched Orchid and found this useful article about relation between color and chemistry of karat gold alloys…

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Cheers! Thanks for all the advice. Happy holidays and good new year !

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Happy Holidays to you as well!

Best
Shan

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Glaedelig Jul, og godt nytar. (Sorry for the wrong letters I dont have a Danish keyboard)

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