How Is Gold Purity Measured?
Gold jewelry is usually not made of pure gold, as this metal is too soft and any items made of it would bend easily. Instead, it is mixed with other metals, such as zinc and copper, and the resulting alloy is harder and more suitable for making jewelry.
Karat is the most widely used measure of gold purity. It is measured on a scale from 0 to 24.
To see how much gold your jewelry contains, look at the stamp indicating its karat.
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.
How to Tell the Karats of Your Gold Jewelry
Determining the karat of gold jewelry can be done by either looking at its karat marks or testing the gold alloy to see how much pure gold it contains.
Gold Jewelry Marks
The karat marks on gold jewelry are usually stamped in places that are not readily visible, and karats are denoted by the sign K or Kt.
The standard karat numbers you are most likely to see are 10K, 14K, 18K, 20K, and 22K.
Another common way of marking gold jewelry is by using parts-per-thousand numbers (especially common in Europe) instead of karats. Parts-per-thousand values can be converted to a percentage by dividing by 10. If that’s the case, you will see a 3-digit number stamped on your jewelry.
For example, the parts-per-thousand mark 583 means that the jewelry contains 58.3% pure gold.
To convert parts per thousand to karats, divide by 1000 and multiply by 24. For instance, converting the 583 mark mentioned earlier, we can see that it is actually equal to 14 karats.
Common Karat Marks on Gold Jewelry
This is how the most common parts-per-thousand purity marks correspond to standard karats:
- 999 = 24K
- 917 = 22K
- 833 = 20K
- 750 = 18K
- 583 = 14K
- 417 = 10K
What Does It Mean If Gold Has “KP” (or “P”) Stamped?
In gold jewelry marked “KP”, 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.
The reason this marking was introduced has to do with the fact that gold sellers are allowed to put a karat number that can differ slightly from the actual gold content of the piece. 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 not lower than what the number indicates.
How Gold Jewelry Is Tested For Karats
If there are no marks on your gold jewelry, you can have it tested for purity.
Most jewelers do such tests, and if you go to a jewelry store, they will most likely use nitric acid to determine the karat of your gold.
The jeweler will scratch your item and take a small sample of its material, and its purity can be determined by the way the alloy reacts with the acid.
How to Test Gold Jewelry for Purity Yourself
You can also test gold for purity at home. To do so, you will need to buy a gold testing kit, which will contain bottles with nitric acid, and follow the instructions included.
See here a jewelry testing kit that you can use to test gold, platinum, and silver.
The principle here is generally the same as that of professional karat testing. The kit will contain several bottles with nitric acid of varying concentration. Each bottle will be labeled with a karat number, such as “10K” or “14K”.
The way most home testing kits for gold work is this:
- First, you need to rub your gold ring, or other gold jewelry, on the testing stone provided in the kit. The jewelry will leave a gold mark on the stone’s surface.
- Then you need to drop a little acid on the gold mark from one of the bottles; for example, the one with the lowest karat number on the label.
- If the mark changes color significantly or disappears gradually, then the karat of the gold is less than the karat number on the bottle’s label.
- If the mark changes color only slightly, then it has the same or approximately the same karat as what the label on the bottle says. (You should expect accuracy of about +/-1 karat.)
- If the mark does not change color, then the gold is a higher karat than the number on the bottle’s label, so you will need to try a bottle with the next higher karat number.
It is recommended that you start with the bottle with the lowest karat number and repeat the process using higher-karat bottles until you zero in on the actual karat of the ring.
This is the basic principle behind most gold testing kits that use nitric acid, although specific instructions and details may vary.
Remember: Always read the instructions that come with the gold testing kit in detail before you start testing.
Converting Gold Karats to a Percentage
Once you know the karats of your gold jewelry, it’s best to convert them to a percentage in order to figure out what part of the gold alloy you have is actually pure gold.
This calculation is straightforward: Just divide the karat number of your jewelry by 24 and multiply by 100.
For example, if you have determined that a gold item is 18 karats, dividing 18 by 24 gives you 0.75, which is equal to 75% gold content.
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)
Weighing Your Gold Jewelry
In order to weigh your gold, you will need a sensitive scale. Don’t weigh your gold jewelry along with any diamonds or other stones it may have – you need the weight of the gold alloy parts only.
If you weigh jewelry of different karats, don’t put all items on the scale, but only weigh together pieces of the same karat.
You can weigh your gold in grams, but many jewelers and gold dealers use troy ounces and pennyweights, so you might need to also convert your measurements to these units.
Let’s see how this is done.
How to Calculate the Amount of Pure Gold in Your Jewelry
After you’ve weighed your gold jewelry, you need to apply the purity percentage you’ve already calculated for each item to its weight in order to figure out how much of it is pure gold.
Calculating the Weight of Pure Gold in Grams
Simply multiply the weight of your jewelry in grams by its purity.
For example, if you have an 18K ring that weighs 7 grams, knowing that 18 karats equals 75% purity, you can calculate that the pure gold in the ring is 5.25 grams.
Calculating the Weight of Pure Gold in Ounces and Troy Ounces
One troy ounce is equal to 31.1 grams, while a regular ounce is equal to 28.34 grams.
So, to convert the weight of your gold from grams to troy ounces, divide it by 31.1, and to obtain its equivalent in ounces, divide its grams by 28.34.
For example, 10 grams pure gold is equal to 0.32 troy ounces, or 0.35 ounces.
Calculating the Weight of Pure Gold in Pennyweights (dwt)
A pennyweight is a commonly used unit of measurement in jewelry and is denoted by “dwt”. One troy ounce contains 20 pennyweights, so a pennyweight is actually 1/20th of a troy ounce.
As a quick conversion guide, 1 pennyweight is equal to 1.56 grams, 0.05 troy ounces, and 0.055 ounces.
So, to convert the weight of your gold from grams to pennyweights, divide by 1.56 (or multiply by 0.64).
How to Value the Pure Gold in Your Jewelry
After you’ve calculated the weight of your gold, perhaps you’re wondering how much it is worth. The answer depends on where you sell your jewelry.
If you sell your gold to gold dealers for scrap gold, most buyers will pay about 60%-80% of the current market price of gold.
If you sell your jewelry at an auction or to an individual, the price will depend on the uniqueness of your items and is hard to predict, as each case is different.
But you should keep in mind that most used jewelry sells at a steep discount to retail prices for new pieces, unless it has antique or collectible value.
What Other Metals Does Gold Jewelry Contain?
Since pure gold is very soft, it is mixed with other metals to create jewelry that is durable. The resulting material is actually a gold alloy.
The metals most often used for this purpose are copper, nickel, zinc, and sometimes, aluminum. The concentration of those additional metals in the alloy can also change the color of the gold jewelry; for example, white gold gets its white color from nickel and zinc.
Where to Buy Gold Jewelry?
For jewelry with diamonds, emeralds, rubies, or sapphires, we recommend James Allen (read review) because it allows you to take a 360-degree look at any stone before having it set in gold.
Blue Nile is another reputable diamond retailer we recommend.
