Gold is a valuable substance, although several factors impact its total value. A question that often comes up is how jewelers determine the value of gold, which is a process that involves making several key assessments. Learn more about this process and the testing involved to determine the value of gold.

How Is the Purity of Gold Determined?

gold bar
Image via Flickr by sprottmoney

You have probably heard of the most widely used purity measure for gold, which is karat. When someone refers to a piece of gold jewelry, they indicate its karat rating to show how pure it is. The karat scale goes from zero to 24, so when a piece of gold has one karat, it includes one part real gold, and the other 23 parts are made of different types of metal or alloys. An 18-karat ring would include 18 parts real gold and six parts other types of metal.

You can further break down the scale into parts per thousand, or the percentage of real gold to alloy or other metal. Simply divide the number of karats of your gold by 24, and then multiply that number by 100. A 20-karat gold necklace would be 83.3% gold, which you’d find by dividing 20 by 24 to get 0.833, and then multiplying that by 100 gives you the percentage. In other words, a 20-karat piece of jewelry has 833 parts of gold for every 1,000 parts.

How Do You Determine the Karat Rating of a Piece of Gold?

A jeweler can typically look at a piece of gold jewelry and find the marking that indicates its karat rating. Most gold jewelry manufacturers include a small indicator on the pieces they produce. A stamp on the piece indicates its karat, although depending on where it was made, the numbers may look different. For example, in Europe, the rating often indicates parts per thousand, so the stamp will show a three-digit number rather than a number within the 0 – 24 scale.

If your stamp includes the number “500,” this would indicate that 500 parts per every 1,000 are real gold, while the other 500 parts are other metals or alloys, meaning it’s 50% gold. You can find the two-digit karat number by dividing by 1,000 and then multiplying that by 24. The 500-gold piece example would be rated at 12 karats. The highest three-digit rating you’ll see on a piece of gold is 999, which indicates 24 karats.

What If a Gold Piece Doesn’t Include a Karat Mark?

karat mark
Image via Flickr by Mauro Cateb

In some cases, gold pieces won’t include stamps or other markings to indicate their karat rating. In the U.S., a law requires that jewelry sold by vendors to include a stamp with a karat marking, but this isn’t the case in all areas of the world. If this is the case with your piece, a jeweler can perform an in-person test to determine its value.

The most commonly used test is with nitric acid, which is a corrosive and colorless mineral acid. This acid reacts with many different materials, including copper-based alloys. When a piece of metal has a high concentration of copper, the reaction between it and the nitric acid is more powerful. Counterfeit gold pieces are generally copper-based, often including materials like tin and copper. Nitric acid also reacts to gold with a low karat rating, although the reaction isn’t as strong as it is to copper-based material.

In a nitric acid test, a jeweler places a few drops of the acid on the piece and watches the reaction. With copper, the reaction usually causes the liquid to turn green, give off fumes, and sometimes bubble. This response is known as a hard cupric reaction and indicates that your piece is not real gold. Lower-karat gold pieces may produce a mild cupric reaction, which includes minimal to no fumes, no color change, and little to no bubbling. You may see a small black mark where the acid came into contact with the piece.

Nitric acid does not react to gold that’s 12 karats and above, nor does it react to stainless steel, zinc, tungsten, aluminum, platinum, or palladium. However, some gold pieces are plated, meaning the outside is gold while the core is another type of metal, so jewelers often test the core to make a better determination on the value.

How Can I Determine If My Gold Jewelry Is Real Gold Myself?

gold ring
Image via Flickr by Franktic1892

Counterfeit gold is common, so it’s helpful to understand some of the properties of this precious metal to determine whether your piece is in fact real gold. The first is that gold is not magnetic, so if you notice that your jewelry or bar jumps toward a magnetic surface, it is not real. Gold also doesn’t corrode or tarnish, unlike aluminum, copper, silver, and brass. Therefore, if you notice any oxidation on your gold piece, it is not completely gold.

Another simple method is the float test. Drop your piece into a glass of water. If it sinks quickly, it’s more likely to be real gold since gold has a higher density than other metals. However, some metals that can pass for gold are also heavy, so this is a good test to try in conjunction with others.

The scratch test is a great way to determine if your jewelry is real gold, but it can damage your piece, so be careful. To perform this test, rub your gold against a piece of unglazed ceramic or porcelain. If the mark left is gold-colored, your piece is very likely real gold. If the mark is black, the piece is not real.

If you have gold and are interested in selling it, you may be able to earn a profit on this highly valuable material. The value of gold fluctuates, but it’s been a valuable metal for centuries. To sell gold or learn more about the process, our team at AaLAND Diamond Jewelers is here to help. For nearly five decades, we’ve built our reputation as one of the top jewelry stores in northwest Indiana, and we’re a local gold buyer who will value your piece fairly and honestly.