You have a piece of gold jewelry that was sold to you as 18 karats, but you are not sure how to check whether that’s true? Let’s see how you can find out the real karat of your 18K jewelry.
18-karat gold jewelry is made of a gold alloy that contains 75% gold and 25% other metals, which make your jewelry harder than the overly soft pure gold.
You can find out the purity of your gold piece by either looking at its karat stamp or testing it for its actual gold content.
Karat Stamps on 18-Karat Gold Jewelry
The most straightforward way to check the karat of your gold jewelry is to look at its surface and see if there are any markings. Gold jewelry usually has its karat number stamped on it.
If your jewelry is 18 karats, it should have a marking that reads “18K”, “18KT” or something similar.
Sometimes, the purity of the gold will not be expressed in karats but in percentages or parts per thousand.
In such a case, the stamp should read “.75”, “750” or a similar number implying that the piece contains 75% gold, or 18 karats.
Sometimes, however, a piece of jewelry sold as 18 karats might have no markings at all.
Or, even though an item is marked as an 18-karat piece, it might actually have lower purity. In such cases, the best way to check the gold content of your jewelry is to subject it to acid testing
Testing 18-Karat Gold with Acid
Acid testing is a way to determine the purity of a gold alloy by putting it in nitric acid and observing the reaction. By the change in the color of the alloy one can establish its gold content.
You can have acid testing done on your gold at a jewelry store for a fee. Usually, the jeweler will take a small sample from your piece to test it.
This is usually done by scratching the item in a place that is not prominent, and the procedure doesn’t leave readily visible traces on the jewelry.
You can also do this test yourself by purchasing a gold testing kit. Click here to see a jewelry testing kit that can be used on gold.
Here’s how you can use such a testing kit to see if your gold is really 18 karats:
1. Scratch your jewelry – usually this is done by rubbing it on a testing stone to leave a gold mark on it. Don’t rub your jewelry in highly visible places.
2. Rub the testing needle labeled “18K” on the stone, next to the gold mark – the needle should leave a mark, whose color you will use to compare with that of the gold mark after it is treated with the acid.
(If your testing kit doesn’t come with karat needles, don’t worry, and proceed to the next step.)
3. Apply some of the acid that is labeled “18K” to the gold scratch mark and the needle mark – this acid is made with the exact concentration needed to react with 18-karat gold.
4. Observe the color of the gold mark. If the gold is 18 karats or higher, its color should not change significantly, if at all. It should look the same as the color of the 18K-needle scratch mark.
If your jewelry is less than 18 karats, its scratch mark should become faint and disappear gradually. If the jewelry is only 1 or 2 karats less than 18 karats, then the mark’s color will become somewhat rusty but not disappear.
Note: Depending on the testing kit you purchase, the testing methodology may differ from the steps described above, so make sure to read the instructions that come with the kit.