We all know that gold is expensive and that pure gold is a symbol of ultimate value. But how do you figure out the purity of gold jewelry in the first place?
How Gold Purity Is Measured
Perhaps you’ve heard of karat (abbreviated K or kt), which is the most widely used measure of gold purity. Karat is measured on a scale from 0 to 24.
Thus, a piece of jewelry that has a purity of one karat consists of 1 part gold and 23 parts other metals or alloys.
Purity can also be measured in percentages and parts per thousand.
To convert karats to percentage, divide the karat number by 24 and multiply the result by 100.
For instance, to figure out the gold percentage in your 20-karat ring, divide 20 by 24, thus obtaining 0.833, or 83.3% gold content (which also translates to 833 parts per thousand).
How to Find Out the Gold Content of Your Jewelry
To see how much gold your jewelry contains, it is usually enough to look at the piece and find the stamp indicating its karat.
For instance, if you see a marking “10kt”, this means that your piece contains 10 parts gold and 14 parts other metals; this karat value also translates to 41.7% gold content.
Sometimes, you will not see purity measured in karats but rather in parts per thousand (especially common in Europe). If that’s the case, you will see a 3-digit number stamped on your jewelry.
For example, if you see the mark “583”, this means that the gold content is 583 parts per thousand. Divide that by 10 and you will get the percentage value of gold content, or 58.3%.
To find the purity of the same piece in karats, divide 583 by 1000 and multiply the result by 24 – the result is 14 karats.
Karat Values and Their Percentage Equivalents
Here are the most widely used karat marks and their corresponding percentages (in brackets you can see the respective parts-per-thousand values):
- 24K – 99.9% (999)
- 22K – 91.7% (917)
- 20K – 83.3% (833)
- 18K – 75.0% (750)
- 14K – 58.3% (583)
- 10K – 41.7% (417)
What Does It Mean If My Jewelry Has “KP” (or “P”) Stamped?
If you come across jewelry marked “KP”, you should know that the “P” stands for “plumb”. This marking means that the piece is guaranteed to have at least the karat value indicated.
For example, if a ring is marked 20KP, it has a gold purity of no less than 20 karats.
But why was this additional marking introduced if the karat number itself is supposed to indicate purity?
The reason has something to do with gold sellers, who are allowed to put a karat number that can differ slightly from the actual gold content of the merchandise.
In the U.S., the permitted deviation is no more than 0.5 karats. So, a ring that is actually 21.5K may be stamped with a 22K mark.
However, if the ring has the letter “P” after the karat symbol, you can assume that the gold purity is at least what the number indicates.
What If I Can’t See Any Marks?
Sometimes, there will be no marks stamped on your jewelry. In such cases, the most accurate assessment of gold purity can be made by a professional.
Usually, jewelers use nitric acid to find out the real karat of a piece. So, if you have unmarked gold and want its purity evaluated, you can always go to a jewelry store and ask to have your jewelry tested.