Gold Testing: How to Tell What Karat Your Gold Is

Updated on April 11, 2018
Beth Eaglescliffe profile image

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

Is your antique pocket watch treasure or trash? A gold assay test will find out.
Is your antique pocket watch treasure or trash? A gold assay test will find out. | Source

Ways to Determine the Karat of Gold

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

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 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. Pure gold is therefore combined with a cheaper base metal to form an alloy.

Copper or silver are commonly used in combination with gold to strengthen it. Thus 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 or jeweler's loupe to see it clearly.

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. I use the Puritest Acid Gold Jewelry Test Kit with scratch stone. The kit consists of six small bottles of acid (one for each type of metal to be tested), a scraper tool and a testing stone. The video below shows how simple the test is to carry out.

How to Test Gold Karat Using Assay Chemicals and Touchstone

Differences Between Fake and Real Gold

 
Real Gold Item
Fake Gold Item
Hallmark
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.
Weight
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.
Price
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."
Malleability
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

How to Tell if Gold is Real or Fake

If you don’t want to do the acid test described above there are other ways to tell if your gold is real. However, they are not as easy to do and may not give such a clear result. The video below describes a few of them.

Indicators that show whether your coin or jewelry is pure gold or fake.

  1. Its weight will show if it has been adulterated with a lesser metal.
  2. Pure gold or silver has a distinct acoustic signature. This can be tested using an app or by using a special acoustic verifying machine.
  3. A magnet will reveal if there is any iron present in the metal. Gold is not attracted to a magnet.

4 Easy Tests to Spot Fake Gold or Silver

How Do Jewelers Test Gold and Why Do You Often Only Get Scrap Value?

Jewelers are shrewd business people. The value of gold fluctuates from day to day. Their ability to accurately assess the value of gold items is essential for them to turn a profit. Their offer to you will be related to the price they can achieve when selling on the item. They use science (objective) and experience (subjective) to test gold.

  1. They will examine your gold trinket using a loupe magnifying glass. They will check the authenticity of the hallmark and feel the weight of the item.
  2. Using acid and a touchstone, they will check the karat value of the metal. The chemical reaction of nitric acid on gold demonstrates the alloy content of the object.
  3. If the jeweler is satisfied with the result thus far, he will look at the quality of workmanship and the integrity of the item. If it is badly damaged, or of poor (tourist) quality, you are unlikely to be offered any more than scrap value.

Bars of gold are an investment vehicle by themselves and turning them into jewelry often does not increase its commercial value. The resale value of secondhand gold jewelry depends on supply and demand and there may be little demand for old-fashioned or dated pieces. Unless an item is individually crafted and of exquisite quality, second-hand values are low as the jeweler will simply be selling them on to be melted down into gold ingots for investors.

Gold bullion. This gold bar weighs 12.5 kilograms ( 27.5 pounds) and is worth about US $500,000 (April 2018.)
Gold bullion. This gold bar weighs 12.5 kilograms ( 27.5 pounds) and is worth about US $500,000 (April 2018.) | Source

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.

The karat value of your gold wedding band and engagement ring determine their color, durability and purchase price.
The karat value of your gold wedding band and engagement ring determine their color, durability and purchase price. | Source

The word “gold” is Indo-European in origin and means “yellow color”. However, the chemical symbol for gold has a different origin. The abbreviation Au derives from the Latin word “aurum” which means “glowing dawn”. This is possibly a reference to the way gold seems to glow in comparison to base metals.

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  • 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

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