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Metal finishing Q&As since 1989


How can you tell when is gold pure?

Q. I melted 11 g of gold points out of aerospace relays, but bar is of color, what else is in it -- palladium, silver, copper?

What can I do to finish refining it?

Justin cutright
Recycler - Stigler oklahoma
June 30, 2023

A. Hi Justin. I know little about gold refining, but I do know that unfortunately you haven't even begun the refining process :-(

Please see Chris Owen's comment on melting gold to purify it.
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

⇩ Related postings, oldest first ⇩

Q. I need to know if it is true that one way to tell when gold has reached its purest level, and all dross has been removed that the fuller looks to see his reflection in the gold? Is this one way to tell?

Janice G Lewis
Pastor - Wilkes Barre, Pennsylvania

A. Janice, gold need not be pure to reflect light well. Is this what you asked?

lee gearhart
Lee Gearhart
metallurgist - E. Aurora, New York

A. As I understand it, a fuller was one who cleaned garments and cloth, mainly to whiten them (Mk 9:3).

No gold is 100% pure, unlike the floor of the New Jerusalem. All gold contains other metals, such as copper and silver, as impurities. Gold is determined as "pure" when it is pure enough to used for manufacturing new products, such as jewelry or electronics. Today, "pure gold" must be from 99.95% (three nines five) to 99.99% (four nines) pure. Gold must be "pure" in order to be sold at near market price. In rare cases, 99.999% (five nines) or 99.9999% (six nines) gold is needed and this is sold at a premium.

Generally, gold is determined as "pure" by its appearance in a bar form. Freshly poured and cooled "pure gold" bars will have a brilliant deep gold color, with NO evidence of discoloration (usually red). On the top surface, you will see a "sink", a place where gases are expelled and the gold has sunk a slight bit. Radiating out from the sink, there are many squarish "crystals", about 1/8" to 1/4" in size. Impure gold has none of these characteristics. Nothing else looks like pure gold.

Sometimes, people buff the bars, in order to make them look purer than they really are. In such cases, the buyer should remelt and repour the bar before he buys it.

When the gold is molten in the crucible, one can tell when it is pure by looking at the surface. It should look very clean and brilliant. There should be no film on the gold. Slightly off-purity gold can many times be made pure by adding periodic pinches of Sodium Nitrate [affil links] (niter), sodium carbonate / washing soda [affil links] (soda ash), and sodium borate (borax). The niter oxidizes the impurities and the other chemicals collect them and bring them to the side, where they are removed with a carbon rod. Eventually, there is clean, brilliant gold, with no film. Sometimes, very pure gold seems to cast a greenish glow.

The thing about seeing your reflection in pure molten gold presents some difficulties. Gold has a convex meniscus, when molten. In other words, at the surface, it curves up in the middle. Although the gold is very reflective, the distorted mirror makes it impossible to tell what is being reflected.

Chris Owen
consultant - Houston, Texas

thumbs up sign What insight! Good question! What a PRO answer! :^ )

Mr. Molder
- Toronto, Ontario, Canada

Q. I teach a Sunday School class of adults and we have been studying about the articles of the tabernacle and the temple in historic Israel. The articles are described as being of "pure gold."

In its purest form, what color is gold?

Thanks for your time,

Alan Hughes
school administrator - Danville, Indiana

Q. Thank you for the help. recently I purchased what presumable was an expensive diamond ring w/ a gold band. black marks in bordering the ring on the other two fingers are showing black marks. could there be any other reason above and beyond a purity issue and can purity be determined by a jeweler?

thank you,

Michael Stephan
- La Jolla, California
February 11, 2008

Q. What if a gold piece marked ".999 Fine Gold" has red discoloration? Should I be concerned? What is it?

Thank You.

D. Shatzkin
- Silver City, New Mexico
September 12, 2009

Q. Is there an easy or simple way that is not subjective? For example, can gold purity be determined by density?

Thanks, Joe

Joe Russell
- Lexington, Kentucky
October 28, 2009

Q. What is more, pure 24 karat or 18 karat?

Rick Morris
- Nampa, Idaho, USA
April 18, 2011

A. Hi, Rick.

Pure gold is 24 karat, whereas 18 karat gold is 18/24's pure.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
April 18, 2011

24 kt Gold Looks Like Copper

Q. I had melted down 21.5 grams gold jewelry which I tested before I melted it. Melted it into a button but it does not look like gold. I tested the button to see what karat it tested and it came back 24K but it looks like a copper button. How do I get out all of the copper out of my gold so it looks shiny like gold should. What do I do? Please help -- want to turn this into a shiny gold bar.

Jerrod Peytn
hobbyist - Springvalley, Ohio, United States
April 25, 2018

A. Hello Jerrod, it is highly unlikely that you had 24k gold purity in the jewelry you melted. The gold in jewelry is alloyed with a number of other metals. If the gold had no alloys it would be too soft for wear. Men's wedding bands are normally 10k gold because the ring is subjected to harsher wear conditions. The button you have most likely has copper metal in it along with other metals. As far as separating the metals (purifying the gold) is something a professional refiner or metallurgist should do.

Mark Baker
Process Engineering - Phoenix, Arizona USA
April 25, 2018

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