You can determine the karate of your gold using a popular method of relative accuracy. This test requires a set of testing needles with different tips of exact karat, a test stone and acids.
Rub a small piece of your item on the test stone and leave a visible deposit. Select the needle that is the nearest to the karat value you believe the gold to be and rub it on the test stone, leaving a visible mark next to your first deposit. Leave a drop of the acid approximating the karat that you believe your item to be.
What to Look for
When the two marks react the same to the acid, then you will know that the gold content (karat value) of your test sample is the same as that of the needle.
When your test sample mark reacts sooner than your needle mark, your test sample has a lower gold content.
When your needle mark reacts sooner than your test sample mark, your test sample has a higher karat value. You can repeat these trials until you are able to find a close approximation of the karat of the gold piece.
When your test proves that your sample has no reaction to the acid, this will reveal that your sample is of higher karate than the acid. In this case you can test again, using a higher test needle and acid until there is a reaction. This way the karat of the gold piece can be determined to a closer approximation.
Pre-mixed acids come in easy-to-use plastic bottles that are entirely secure, and come with color-coded caps. You can use these acid tests on jewelry that has been properly filed to reveal the base metal (if any.) You can use pre-mixed test acids for your 10K, 14K, 18K, 22K gold.
Gold Testing Procedures
Scratch your piece over the surface of the black stone as provided, pressing well enough to leave a visible deposit. A line of one to one-half inches long is suitable. For those looking for the most accurate testing available it is important that the user becomes familiar with "comparative testing" which uses standard gold testing needles. For the best in sensitivity, leave a scratch line along side the scratch line of the metal that you are testing with a gold test needle. Take note of the speed at which the scratches dissolve. If your test scratch dissolves more quickly than your needle scratch, you have a lower karat than the test needle.
Leave a drop of the 10K solution on the scratch made. Should the solution dissolves your scratch on the stone this indicates that the object is less than 10K gold or not even gold at all. Should the solution leave your scratch intact, your object then will be 10K or greater than 10K.
You can repeat as above using the 14K solution. If the solution dissolves the scratch on the stone you will have less than 14K gold (if the scratch dissolves slowly and leaves rusty color particles, it is likely 12k gold.) If the solution does not affect the scratch, your object is 14K or greater than 14K.
You can repeat as above using 18K solution and 22K solution (when available) to find the exact karat of your object.
Keep in mind that when the solution used dissolves the scratch slowly and leaves rusty color particles it is likely two karats lower than the solution being used.
For your heavy weight and volume chains, coins, etc., where plating can hide the true metal, scratch a deep notch in the test piece and do you're testing on the metal inside the piece.