Instead, it is mixed with other metals, such as zinc and copper, and the resulting alloy is harder and more suitable for making jewelry.
To calculate the actual amount of pure gold in your jewelry, first you need to know its weight and karat.
Determining 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 instead of karats. Parts-per-thousand values can be converted to a percentage by dividing by 10.
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.
Karat Testing for Gold Jewelry
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.
You can also do such a test at home. All you need to do is buy a gold testing kit, which will contain bottles with nitric acid, and follow the instructions included.
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.
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.
Determining 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).
Valuing 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.