You can also test gold 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 for gold work is this:
Fist, you need to rub your gold ring, or other gold jewelry, 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.