Throughout history, gold has been considered a precious metal and one of its primary uses has been to make jewellery and decorative objects. The carat measurement refers to the purity of gold. In jewellery, 10 carat is the lowest purity (and the densest), while 24 carat is very soft and nearly pure. Sometimes that carat purity is marked on jewellery, but a simple test can resolve any questions.
Learn what carat refers to. Because gold is a soft metal, it is alloyed with other metals to improve its durability and strength. When it is alloyed with other metals, the carat measurement is used to indicate the amount of gold present. Twenty-four carat is pure gold and it is alloyed down to 10 carats. Items less pure than this are sometimes called gold-filled, gold plated or gold washed.
Look for markings on the piece. Typically, gold jewellery is marked with a number plus the letter K, to signify the carat purity. So, 10K is 10 carat gold and 24K is 24 carat gold. This will typically be on the clasp for necklaces and bracelets, on the inside of a ring and on the post of earrings.
Use a gold testing kit. A gold testing kit uses acids to determine the gold purity. A typical testing kit has separate bottles for 10K, 14K, 18K, 22K and 24K gold. To use, scratch the jewellery on the stone that is provided in the kit. Scratch in a protected area, such as the inside of the clasp, as it is a destructive test. The kit will have instructions as to the exact usage. The length of time the acid takes to dissolve is an indicator of the gold's purity.
There may be mailing restrictions on acid kits depending on the state you live in.
Take care when using the acids as they are highly toxic.