Testing Gold Jewelry for Its Purity

You inherited a piece of jewelry, let’s say, and you are curious about how many karats of gold are in it. Of course you can take it to the jewelry store and pay them to test it. Or if you’re the DIY type, you can test it yourself.

What You Will Need

First off, buy a gold testing kit. It will contain enough nitric acid to test several pieces of jewelry. It shouldn’t cost more than $25 at the most. Then assemble the jewelry you want to test, and test them one at a time.

Keep in mind as you do this, you are working with acid. You may wish to wear rubber gloves and have water handy just in case some gets onto your skin. Also, be sure to keep this material out of reach of small children. It’s a good idea to read the instructions before you start the test.

The Testing Process

Then take the stone provided in the kit and transfer a tiny bit of the metal to the stone by rubbing or shaving the jewelry in an inconspicuous place. There will be several bottles of acid of varying concentrations in the kit, marked with different karat values, such as 10K, 14K and so on. Take the lowest bottle, usually 10K, and place a drop of acid from the bottle onto the material from the ring. Then watch the metal to see if it changes color. If it remains about the same or doesn’t change much, then that is the approximate karat of the metal (aka the percentage of the actual gold in the ring).

If the gold gradually disappears or changes color, then you have less than 10 karats of gold in the piece.

If, instead, the gold doesn’t change at all, the karat value is higher than 10K

So, assuming the color doesn’t change, then you would apply the acid from the next highest labeled bottle – probably 14K – and repeat the process. The process is repeated until you find the acid that doesn’t change the gold shaving.

Thus you will arrive at an approximation of the karat or purity of the gold.

Pure gold is 24 karats, meaning it contains no other metals. You don’t find 24 karat gold in jewelry, though, because the metal Is so malleable, or soft, that it won’t hold its shape. So harder metals must be mixed, or alloyed, with it. What you are doing is finding out how much gold is actually in the jewelry. Naturally, the higher the karat, the more valuable the jewelry.

Sometimes the karat is stamped onto the jewelry, so testing isn’t necessary. You will see a number followed by K or Kt. Or you may see a number expressed as parts per thousand. 18 karat gold would be expressed as 750, or ¾ pure gold. 10 karat would be 417, and so on. These numbers are derived as follows: karat number divided by 24 and multiplied by 1000. Thus 18 divided by 24 is .75 x 1000 = 750.

There. You just added another skill to your DIY list. Your mother would be proud.