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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Fineness of Gold is Lower After Smelting
Q. I would like to know why when I send gold bullion (60-88%fineness) for refining, the refiner smelt and give a new weight (always lower than the weight we sent, e.g 4020 oz will give say 4005 oz - lost 15 oz).
2. The assay also lower, e.g., before smelt - 88.98% but after smelting - 87.23%. Is it can be accepted?
Thank you.
Mohd Isa- Pahang, malaysia
2003
A. Dear Mr. Isa,
You asked 2 questions about the refining of your scrap gold ingots.
The first was melt losses when your scrap ingots were remelted. A melt loss of less than half a percent is not unusual with scrap gold alloys as the metal often contains zinc and other oxidizable metals that burn off or end up in the slag.
As for the assays, if you are taking drilled samples off the bottom of your gold scrap ingots, they may not be representative of the whole ingot. Molten pin samples should be drawn with a glass tube out of the molten metal before pouring your gold scrap. Most refiners use this method as it is the most accurate sampling method. It might be advisable for you to pull a molten pin sample and ask your refiner for a pin sample of your metal. Label the samples and send them to an independent assayer. This should help clear up your problem.
Best regards,
Jim Sivertsen- Alden, New York, U.S.A.
2003
byG. Gore
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Q. What is the difference between 9k, 18k gold, etc?
Jamie Penn- UK
2004
A. Pure gold is 24K, Jamie, but too soft to use in a lot of complex jewelry, so gold is usually alloyed with other metals for jewelry. 9K gold is 9 parts gold out of 24; 18K gold is 18 parts gold out of 24, so it's roughly twice as expensive as 9K.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 9, 2009
Q. Hi I have a similar question but perhaps slightly more complicated.
I am going to get my partner to supply gold dust at 92% purity. I will then export to my buyer.
Of course to my buyer I have to discount it according to LME prices because the gold is 92%.
I am thinking of getting it smelted to increase the value. Our customer has agreed to buy the dust but I am thinking if I can increase purity by 5% or more I will get more money for final product I am selling. (5% price increase!)
This deal I am getting paid on the gross weight being sent to the refinery in buyers country.
Here's my question:
1) If I smelt the gold at 92% and it becomes 97+ percent purity I will increase the price by 5%
So, for 1KG what approx. loss should I expect in weight.
I do not want the 1KG gold dust (92%) to be smelted and then I eventually deliver 500 Grams.
2) Will I increase my margin or will the loss in net weight after smelting make this non commercially viable?
Or maybe the loss will offset the gain and it will be worth the same value?
A) To simplify the whole question: how beneficial is it to smelt? Thanks for your help. Regards, Maurice.
trade - London, England
Permissable gold losses in refining
Q. Hello,
I wonder if I can have an answer for the gold losses ratio after refining process? Usually in my refinery, we issued the gold from the vault room to the refinery, in different carats of gold. That is, for refining the impure gold batches/quantities to pure gold (999.9). Then casting the quantity in different weight of bars with stamping. The question is: what is the permissible gold losses after the entire process, of the following carats?
(24 carat, 999.9), (22 carat, 916.7), (21 carat, 875.0), (18 carat, 750.0), (14 carat, 583.33), (12 carat, 500.0) and (9 carat, 375.0).
Best wishes,
precious metals refinery - Jeddah - Saudi Arabia
November 14, 2016
A. Hi Salim,
permissible gold losses you can achieve from your past data evaluation. Basically it depends on how much impurities contained in your refined material. Also combustible material contained.
Ex., if you're refining 18k metal to achieve 24k 999.9 gold. 25% is your loss (1 - 18/24)%. That is your alloy but when melting and refining losses occurs which may increase due to composition of alloy also. Remember your alloy may contain volatile component. I had faced a problem in Lux-105 progold alloy.
CAC admixtures - Mumbai, India
December 26, 2016
Q. Hello,
I have a question, I'm a manufacturing jeweler and have been told in the past by a metallurgist and refiner that every time that you reuse gold and remelt (without refining) the gold purity decreases. So say leftover 18 kt yellow gold pieces after remelting would be say 17.8 kt or something like that, is that true?
- Sydney, NSW, Australia
July 6, 2017
A. The gold percentage in the poured bar would either remain the same or it would increase slightly, due to a portion of the copper or other base metal being oxidized and going into the slag. In this case, there would be at the same time a proportional decrease in the total amount of metal, due to this small loss of copper.
The gold percentage in the alloy would not decrease because the gold will not oxidize under these conditions. The only way gold can be lost when melting is if small beads of the molten karat alloy are mechanically hung up in the slag. However, this won't change the gold fineness hut it will affect the final weight of the alloy.
- Benton, Arkansas, USA
July 6, 2017
Thanks Chris. I always found that hard to believe, thanks again for clearing it up.
- Sydney, NSW, Australia
July 7, 2017
Q. My name is Anthony
I have just started prospecting a month ago and staked my first placer claim on a local creek. I have panned about 17 grams of fine flour gold about 200 microns what would be the purity of this type of placer gold before smelting. I am also thinking of smelting my gold at home using anhydrous borax
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flux with sodium bicarbonate (baking soda). I know from research that you use 1 teaspoon of borax flux to 1 ozt of gold -- what would be the amount of baking soda? I'm not sure if there are any impurities in the gold as it may be too small for such impurities like copper, iron, silver, etc., to attach to the gold.
My question: If I smelt my own flour gold will my purity increase to 99.99% 24k pure fine gold or will I not be able to achieve that level of purity?
- Sedro Woolley, Washington
August 5, 2020
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