Gold Testing: How to Tell What Karat Your Gold Is

Updated on January 8, 2018
Beth Eaglescliffe profile image

Science graduate and business advisor, health educator and author, Beth writes articles on a wide variety of subjects.

The gold hallmark shows the karat rating. Here it is inside the scissor handle.
The gold hallmark shows the karat rating. Here it is inside the scissor handle. | Source

Ways to Determine the Karat of Gold

Look at the color
The deeper the orange-yellow color, the higher the karat.
Check the hallmark
Are the assay marks clear and are they from a country that you can trust?
Carry out an assay test
Take care. Wear protective clothing as you will be handling acid.

Karat Is a Measure of the Purity and Value of Gold

The value of gold is determined by its fineness or karat rating. An object made from 18-karat gold will cost you more than the same object made from 9-karat gold. An experienced jeweler will often be able to guess the value of an item just by looking at it, but they also carry out tests to determine the karat rating of gold. Knowing how a jeweler determines the karat value will help you, should you ever be buying or selling gold.

Karat (spelled "carat" in the UK) is a measure of the fineness and quality of gold. That is, the amount of gold relative to other metals that make up an object. In US and Canada, the most frequently used karat values are 14 karat and 18 karat (meaning 58.5% and 75% gold respectively). In UK, 9, 18 and 24 carat gold are the most frequently used alloys.

The higher the karat value, the greater the proportion of actual gold metal in your object. For example, an 18 karat gold ring will be made from 75% pure gold and 25% base metal (or alloy). A 9 karat gold ring will contain only 37.5% pure gold.

The color of gold depends on the amount and type of alloy metal used.
The color of gold depends on the amount and type of alloy metal used. | Source

Gold Varies in Color From White to Red

There are many variations in the color of gold, ranging from white through yellow to deepest red. Pure gold is a deep golden yellow-orange. In its purest state it is very soft, and although this makes it very easy to work with, for everyday use a harder metal is needed. Gold is therefore combined with a cheaper base metal, commonly copper or silver, to form an alloy.

What is commonly referred to as "white gold" has a high proportion of silver in the alloy. Similarly, "red gold" contains a lot of copper in the alloy.

A type of magnifying glass known as a loupe enables the fine detail of hallmarks to be read.
A type of magnifying glass known as a loupe enables the fine detail of hallmarks to be read. | Source

Assay Marks and Hallmarks

"Assay" means “a test." A gold assay test shows the percentage of gold in relation to other metals in an item. It is a test of value rather than of quality. Expensive materials can be poorly manufactured and, similarly, cheaper metals may have been worked with exquisite craftsmanship. An assay or hallmark is an objective chemical test. Deciding the quality of an object is subjective.

Hallmarks show that an assay test has been carried out on the gold object to confirm its karat rating. The reliability of the hallmark depends upon the country of origin. State-controlled assay offices imprint a mark onto the gold showing the year and place of assay together with the percentage of gold found, or the karat rating. The hallmark is very small so you may need a magnifying glass to see it clearly. A Stalwart jeweler's loupe is a special magnifier glass used in the jewelry trade.

If the hallmark is clear and easily readable, this is the quickest way to check the gold content of an item. However, over time some of these marks can become worn, and some may have been deliberately tampered with. So how do dealers determine how much a gold item is worth if the karat mark is indistinct or missing? There are several ways to do this, as explained below.

Assay tool kit with touchstone and acid vials.
Assay tool kit with touchstone and acid vials. | Source

Test the Karat of Your Gold at Home

The only way to determine for sure an object’s karat value is to carry out an assay test. All jewelers and gold dealers will use an assay test kit before they purchase a gold item.

The kit consists of a number of different solutions of dilute acid and a touchstone. The touchstone is made of a dark acid-resistant rock such as slate. The jeweler rubs the gold object gently across the stone so that it leaves a streak mark. He or she then applies the acid solutions in turn to the mark. The higher the gold content of the metal, the less of it will vanish when acid is applied.

These chemical kits can be bought on-line for home use if you want to check the karat of your own gold items. A simple to use and reasonably priced kit is the Testing Acid Jewelry Test Kit with scratch stone. The video below shows how simple the test is to carry out.

How to Test Gold Karat Using Assay Chemicals

Gold is an Inert Metal

One of the reasons why gold is such a prized metal is that it is chemically inert. This means that it does not react to air. Gold does not oxidize (i.e. rust) like so many other metals.

Gold also does not cause skin irritation if worn as jewelry. Discoloration or rashes on the skin next to the jewelry indicate that the gold has been adulterated with a base metal.

Gold watch showing assay markings.
Gold watch showing assay markings. | Source

Differences Between Fake and Real Gold

Real Gold Item
Fake Gold Item
Should clearly show the year and location of the assay test center. Consult reference books to confirm that you have a genuine hallmark.
Hallmark may be illegible or missing.
Gold is heavy. You can feel the weight of it in your hand.
Be suspicious if the object is lightweight. Gold-plated items may fool you by looking like solid gold until you judge their weight.
Compare prices before buying so that you have a good idea of the correct market value.
Remember the old adage. "If the price sounds too good to be true, then it probably is."
Pure gold is a very soft metal and will dent easily.
A gold-plated item will be harder because the gold is just a thin coating over a tougher base metal.
Acid Test
Gold does not react with nitric acid.
A lesser metal will foam or dissolve when a drop of nitric acid is applied.
Gold hallmark from the Soviet Union.
Gold hallmark from the Soviet Union. | Source


Submit a Comment

  • john000 profile image

    John R Wilsdon 2 years ago from Superior, Arizona

    this discussion about testing gold was very good. I particularly appreciate the reference to assay gold testing kit. Many prospectors would be happy to know how simple it is to get a testing kit. I know the use of acid requires safety measures, but so does prospecting! Thanks again for an informative hub.

  • annart profile image

    Ann Carr 4 years ago from SW England

    Very interesting. I generally prefer to wear silver but as I've got older I've worn more gold and the deep golden colour is beautiful. I love the 'slave bangles' where you have one bracelet white gold, one yellow and one red; they go together very well. In fact, I like mixing my silver and gold jewelry, even on one finger. Up, useful & interesting. Ann