A gold ring is one of the most common pieces of jewelry, but how exactly can you find out its karat? Let’s see how gold rings are tested for karats by jewelers, whether you can do such a test at home, and what the test results mean.
How Jewelers Test Gold Rings for Karats
One of the most common ways jewelers determine the number of karats for a gold ring is by testing it with nitric acid, whose reaction with gold alloys varies depending on their karats.
Usually, a tiny shaving is taken from an inconspicuous spot on the ring, and a drop of acid is applied to the sample.
The jeweler will observe the reaction between the acid and the material, and based on the change in the color of the gold, its karat will be determined.
This is one of the most common methods for determining karats. Gold rings can be tested this way at most jewelry stores, which provide such services for a fee.
Can You Test a Gold Ring for Karats Yourself?
You can also test a gold ring for karats at home. To do so, you will need to buy a gold testing kit.
The principle here is generally the same as that of professional karat testing. The kit will contain several bottles with nitric acid of varying concentration. Each bottle will be labeled with a karat number, such as “10K” or “14K”.
The way most home testing kits work is this:
- Fist, you need to rub your gold ring on the testing stone provided in the kit. The jewelry will leave a gold mark on the stone’s surface.
- Then you need to drop a little acid on the gold mark from one of the bottles; for example, the one with the lowest karat number on the label.
- If the mark changes color significantly or disappears gradually, then the karat of the gold is less than the karat number on the bottle’s label.
- If the mark changes color only slightly, then it has the same or approximately the same karat as what the label on the bottle says. (You should expect accuracy of about +/-1 karat.)
- If the mark does not change color, then the gold is a higher karat than the number on the bottle’s label, so you will need to try a bottle with the next higher karat number.
It is recommended that you start with the bottle with the lowest karat number and repeat the process using higher-karat bottles until you zero in on the actual karat of the ring.
This is the basic principle behind most gold testing kits that use nitric acid, although specific instructions and details may vary.
Remember: Always read the instructions that come with the gold testing kit in detail before you start testing.
Karat Testing Results: What Do They Mean?
To interpret what the results of a karat test mean, simply think of karats as the parts of pure gold that an alloy contains.
In karat notation, the maximum gold content in an alloy is 24 parts, which corresponds to 100% pure gold, so 1 karat purity is equal to 1/24th gold content.
Thus, for example, if a ring is 18 karats gold, this means that 18 out of 24 parts are pure gold, and the remaining 6 parts are other metals.
Common Karat Marks on Gold Rings
You won’t always need to have a gold ring tested to determine its karats.
If there is a karat mark on the ring, usually on the inside of the band, then you can easily find out its purity, assuming you have no reason to doubt the mark.
So, if you see a number followed by the symbol K (as in 18K), or KT, this should be the karat of the ring.
Sometimes gold marks are not in the form of karats but represent purity in parts per thousand. In such a case, you will see a three-digit number instead of a karat stamp.
This is how the most common parts-per-thousand purity marks correspond to standard karats:
999 = 24K
917 = 22K
833 = 20K
750 = 18K
583 = 14K
417 = 10K
Conversion principle: Purity expressed as parts per thousand is equal to the karat number divided by 24 and multiplied by 1000.
Conversely, multiplying a parts-per-thousand number by 24 and dividing it by 1000 will give you the respective karat.