What is the percentage of gold that can use aqua regia?

[nattawat]

I have another question about refining gold. I like to know the minimum percentage of gold that can use aqua regia for refining. I heard that the maximum of silver is 10%. Is it correct? moreover, the lower percentage of gold and higher percentage of gold which one is faster for dissolve the gold by using aqua regia. I heard higher percentage of gold is faster when use aqua regia. Am I right? because someone told me that if the content of gold is low it will be faster.

 

[SilverNitrate]

If karat gold, the higher the purity the faster it will dissolve. 18k will be a bit faster than 10k. Also if there is a high content of silver then the reaction will be slow. Hencewise a 10k white gold class ring seem impossible to dissolve and a 22k bracelet will disappear rapid.
Higher silver content is harder because the silver chloride formed at the surface prohibits the gold/copper from going into solution.

 

[Harold_V]

If karat gold, the higher the purity the faster it will dissolve. 18k will be a bit faster than 10k. Also if there is a high content of silver then the reaction will be slow. Hencewise a 10k white gold class ring seem impossible to dissolve and a 22k bracelet will disappear rapid.
Higher silver content is harder because the silver chloride formed at the surface prohibits the gold/copper from going into solution.

Assuming a 10K ring is white gold, not some unusual alloy (common after the increase in the cost of gold in 1980), you are misinformed. There is NO silver in white gold, but nickel instead. It readily dissolves in AR.
What limits gold's ability to dissolve in AR is not the gold content, but the silver content. So long as the silver content is below 10%, some degree of success will be achieved. The lower the percentage, the greater the success. Too high of a silver content results in a hard coating of silver chloride forming that isolates the parent metal from the acid in use, eventually leading to a complete cessation of dissolution.

Harold

 

[samuel-a]

Harols

how can white gold 10-14K be tested, meaning if it contains Pd or Ni ?

 

[goldenchild]

Harols

how can white gold 10-14K be tested, meaning if it contains Pd or Ni ?

I learned this from a jeweler. He said many jewelers are unconfortable testing for platinum as other metals have similar qualities when doing a rub/acid test. Many people bring in white gold thinking its platinum or the inverse. So he showed me side by side what a platinum and white gold rub look like. The platinum is a brilliant silver like color while the white gold has a yellow hue. That color is very distinct. Also remember that Pd and Ni will submit to 10k and 14k acid as 10k is just straight nitric acid and 14k is a watered down AR. When you put them on the white gold rub a yellow streak will be left behind like you're more accustomed to seeing. Like everything, experience will be a big contributing factor.

 

[Harold_V]

Harols

how can white gold 10-14K be tested, meaning if it contains Pd or Ni ?

Considering both nickel and palladium will dissolve in nitric acid, a destructive test would be to dissolve a trace of the metal and test with DMG. It alone will test for both metals. If the alloy is made with palladium, DMG will yield a bright yellow precipitate. If there is no precipitate, the addition of a drop of ammonium hydroxide and a drop of DMG will yield a beautiful pink reaction, assuming the alloy is made of nickel.

For 10K alloy, it's entirely possible a drop of nitric placed directly on the item will yield enough solution to be tested. The area tested will likely be slightly discolored, but can be restored easily by a light buffing.

Goldenchild's comments are certainly worth reading.

Harold