Gold Testing: How to Tell What Karat Your Gold Is

Updated on June 24, 2020
Beth Eaglescliffe profile image

Scientist and author, Beth enjoys the beauty and craftsmanship of real gold jewelry.

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

How to Identify Gold at Home

Jewelers and gold dealers carry out a metal assay (or test) before they purchase a gold item. This is the only sure way to find out if an object is made of real gold.

An assay test kit contains several different solutions of dilute nitric 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 touchstone so that it leaves a streak mark. They then apply each of 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 assay kits can be bought on-line for home use, so you can check the karat of your own gold items. I use this Gold Jewelry Acid Solutions Test Kit. The kit consists of six small bottles of acid (one for each type of metal to be tested), and a testing stone.

How to carry out an assay test:

  1. Softly scratch the item of jewelry with the testing stone, so that it leaves a gold mark on the touchstone.
  2. Place a drop from an acid bottle on the mark. Start with the lowest karat value test and then work upwards.
  3. If the gold mark doesn’t change in color, or dissolve, then it is of a higher karat than the assay.
  4. Continue testing with the higher-karat acid bottles, and repeat until the gold mark starts to change or dissolve. This will indicate that its karat is less than that written on the label of the last acid bottle you used.

How to Test Gold Karat Using Assay Chemicals and Touchstone

Karat Rating Measures Gold Purity and Value

Karat (spelled "carat" in the UK) tells you the percentage of real gold in your jewelry relative to other metals. It indicates the fineness and quality of your item. The higher the karat value, the greater the proportion of actual gold metal in your object. 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.

In the US and Canada, the most frequently used karat values are 14 karat and 18 karat (meaning 58.5% and 75% gold respectively). In the UK, 9, 18 and 24 carat gold are the most frequently used alloys.

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.

Gold watch showing assay markings on reverse.
Gold watch showing assay markings on reverse. | 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.
It's difficult to tell just by looking at it the karat value of gold jewelry.
It's difficult to tell just by looking at it the karat value of gold jewelry. | 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 you trust?
Carry out an assay test
Take care. Wear protective clothing as you will be handling acid.

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. A jeweler will examine your gold trinket using a loupe magnifying glass. I always take a 20 x jeweler's loupe with me when buying jewelry so that I can do the same. Using a loupe means the fine detail of any hallmarks can be read. The jeweler 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 their 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.

What Acid is Used in Gold Testing Kits?

Nitric acid is used to test the purity of gold objects. Gold is the only metal that is dissolved by this acid. A tiny scrape of the gold item is placed on a touchstone. Nitric acid reacts when brushed onto real gold and you will see fizzing if your gold jewlelry is genuine.

A retail metal testing kit (I recommend a good one in the first paragraph of this article) consists of several different strengths of acid solution. The different levels of nitric acid enable you to test for different karat numbers.

Can Vinegar be Used To Test Gold?

Vinegar (ascetic acid) can be used to clean some metals. It is not really a testing fluid, it is more of a cleaning agent. If you rub an object made of pure gold with neat vinegar it will remove marks and leave your jewelry shiny and clean. However, if the metal is not real gold, the acid will cause pitting (small holes) on the surface and your ring or bracelet will be damaged.

  1. Pour some white vinegar into a glass container. Do not dilute with water.
  2. Place your gold item into the liquid and leave for 15 minutes.
  3. Remove your gold pieces and rinse well in clean water.

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.

How to Spot 9, 14, 18, 22, and 24 Carat Gold

Percentage Pure Gold
Naturally yellow and highly valuable, but very soft. Not usually used to make fine jewellery.
Also very soft, so not ideal for stone set jewellery. Used for plain gold jewellery, such as wedding bands.
Contains metal alloys for strength and color. White metals added to create white gold. Copper added to create rose gold. 18ct yellow gold is brighter in tone than 14ct and 9ct gold.
More affordable than 18ct gold, due to its lower gold content.
Contains a high percentage of other metals, making it stronger and cheaper to buy.
Information from "Gold Carats Explained"

Gold Is Inert (Non-Reactive to Air)

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

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.


Submit a Comment
  • john000 profile image

    John R Wilsdon 

    5 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 

    6 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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