How can you tell when is gold pure?

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,


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

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

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 ⇦ this on Amazon [affil link] (niter), sodium carbonate ⇦ this on eBay or Amazon] (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.

A. Hi, Rick.

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

Regards,

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.