The value of gold depends on two factors; how much the gold weighs and how pure it is. The science of measuring the purity of gold is assaying. Professional assayers typically use specialized laboratory equipment to certify the purity of gold down to the number of micro-particles. While this is not practical for the average person to do on their own, some methods will give a more general measure of the purity. One such method is to perform a scratch test, which will allow you to verify how many carats the gold is.
Things You'll Need:
- Touchstone
- Testing Keys
- Testing Solution
Step 1:
Visually inspect the gold. Look for any stamps or other markings that will identify the purity of the gold, particularly if the item is a piece of jewelry. Although these stamps are not always accurate, they will give you a good early indication of what you are working with so that you can narrow the number of testing keys you use.
Step 2:
Scratch the source gold on the touchstone. Find an obscure place on the item so that scratches will not be immediately evident. Press down firmly and rub the gold back and forth several times, so that the gold is scratched against the surface of the stone.
Step 3:
Scratch the test keys on the touchstone. Select two or three testing keys that you feel are probable matches for the source gold. Firmly scratch each key on the touchstone in an area near the scratch of the source gold. Remember which scratch belongs to which testing key.
Step 4:
Drip one to two drops of testing solution onto the scratch test area. Note that the scratches begin to change colors, with each degree of purity being a different color.
Step 5:
Look at the color of the scratches. Compare the color of each scratch to the color of each tuning key. Matching the color of the scratch with the color of the key will tell you that the source gold is the same purity as the key that made that particular scratch.
Tips:
Using a scratch test is not a scientific measurement of purity. It is, however, an accurate assessment for on-the-spot verification of gold purity.
References:
- Ruby Lane: Precious Metal Testing: A Beginner's Guide
- Shore International Corporation: Instructions for Scratch Testing Gold, Platinum and Silver
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