The acid test can be used to authenticate gold, silver, or platinum. It determines authenticity and purity based on how the metals react to acid.
A typical kit comes with six bottles of acid. One bottle for 10K gold, one bottle for 14K gold, one bottle for 18K gold, one bottle for 22K gold, one bottle for silver testing, and one bottle for platinum testing.
In addition to the bottles of acid, a kit typically comes with one or two rubbing stones (usually black in color), a loop (jewelers magnifying glass), a digital scale, a portable diamond tester, a testing platform, a 9v battery, one or two jewelers files, and instructions.
To perform an acid test on gold, you would do the following:
First,check the markings that indicate karat weight (that’s what the loop is for). Remember, you are doing this to authenticate, so you do not know if it is properly marked of if it is real at all. Don’t ever rely on the karat marking as being accurate. You are checking the marking as a reference comparison to the result of the test. Once you have identified the karat marking, you would:
- Rub the item that you’re testing on the rubbing stone until you see the gold residue on the stone.
- Beginning with the 22k acid, put a drop on top of the gold residue on the stone. Wait a few minutes. If the acid does not eat through the residue, then the gold is 22k or higher. If the acid eats through the residue, then it is not, and you will need to continue testing. To continue, clean the stone with a rag and repeat the test using the 18k acid. Continue repeating this process with each (lower karat) acid until the gold residue does not corrode when the acid is applied.
- Just remember that this test is not appropriate for determining the exact karat weight of a particular item. It is used to determining if an item is real gold, and in doing so, it will indicate a karat weight range. For instance, if the item eroded using the 18k acid, but did not erode using the 14k acid, we can expect that gold in that item to be at least 14k, but less than 18k.
This is a very useful and relatively inexpensive way of determining authenticity. This method also has its limitations. Specifically, if an item is not solid gold, but instead it is gold plated (or on the contrary gold filled), you will only get an accurate result for the outer veneer of the item.
To further the test under these circumstances, you should first apply the test above. After you determine the gold is real, cut a notch in the item using a jewelers file. Then apply a drop the acid you just used directly to notch you cut in the item. If the acid remains clear then it is a safe bet that it is the same karat weight of gold that the rub test confirmed.
For testing silver, follow the same procedure described above and then match the color of the acid to the description below to determine the purity:
Bright Red = Fine Silver
Darker Red = 925 Silver (Sterling Silver)
Brown = 800 Silver
Green = 500 Silver
Yellow = Lead or Tin
Dark Brown = Brass
Blue = Nickel