There are many ways to test for the purity of gold, but some of these methods are either destructive to the material or require very expensive equipment, expertise knowledge, and special procedures.
One of the quickest and most cost-efficient ways gold purity can be tested is by using the “Touchstone” method. This is an old and reliable technique which can keep gold jewelry and coins intact. The touchstone method uses acids, white/yellow gold testing needles (with known gold purity listed on each side), and of course, a “touchstone”.
Before attempting to test for the purity of gold, it is first checked for any stampings or quality marks that may indicate its purity. The US uses the Karat “K” system for marking gold, whereas Europe uses three digits indicating the percentage of gold in their jewelry. The equivalents are as follows:
- 24K; 999 Mark: 99.9% Gold purity
- 22K; 917 Mark: 91.7% Gold purity
- 18K; 750 Mark; 75% Gold purity
- 14K; 585 Mark: 58.5% Gold purity
- 10k; 417 Mark: 41.7% Gold purity
Sometimes, the appraiser will first perform a “nitric acid test” to check if the item is actually gold. In this test, a small mark is made in a hidden area and a drop of nitric acid is applied. If no reaction occurs, then it is necessary to proceed with the touchstone test.
The purity is measured by following these steps:
- The jewelry piece is rubbed against the touchstone (using an inconspicuous spot) until there is a thin but clear metal sample on the stone. It is marked as the unknown metal.
- Using the gold testing needles, a line is made for each of the other needles of suspected purity (12K, 14K, & 18K) which are also marked accordingly.
- The test starts using the lowest Karat acid bottle (12K in this case). An applicator is used to swipe the acid across all the lines of the metal samples. After 20-40 seconds the touchstone is rinsed with a mixture of water and baking soda to neutralize the acid and is rinsed again with water.
- This will cause the 12K gold testing needle line to disappear. If the line of the jewelry piece being tested has disappeared, this means it has a purity of roughly 12K or lower (which may need to be tested for by trying it against the 10K solution). Thus, it is recommended to have a lower Karat line for control purposes.
- If the line of the jewelry piece remains, then it proves it is higher than 12K and the process is repeated with the 14K acid bottle. If at 14K the line of the piece disappears, then its purity has been determined. If not, the stronger acids are used until the line disappears.
There exist other simple ways to test for gold purity. If you are interested in acquiring a gold appraisal kit, Cash for Gold Mailer provides a fast and safe way to determine your gold’s value. After performing their own purity test and weighing your jewelry, they’ll offer you a cash payment based on the spot price of gold.