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Gold Testing: How to Tell What Karat Your Gold Is

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

Even gold bullion needs to be tested to determine its purity.

Even gold bullion needs to be tested to determine its purity.

How to Test Gold Quality 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.

Assay kits can be bought online 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

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 30 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.

Assay Marks and Hallmarks

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.

Jewelers use a magnifying glass known as an eye loupe to examine the hallmark.

Jewelers use a magnifying glass known as an eye loupe to examine the hallmark.

Karat Rating Measures Gold Purity

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.

How to Tell if Gold is Real or Fake

The acid test described above is the best way to determine whether or not an item is made from real gold. There are other ways to tell if your gold is fake, but they may not give such a clear result.

  • Look at the color: The deeper the orange-yellow color, the higher the karat.
  • Weight of the item: Too light indicates it's been adulterated with a lesser metal. Gold is heavy. You can feel the weight of it in your hand. Be suspicious if an object is lightweight. Gold-plated items may fool you by looking like solid gold until you judge their weight.
  • Sound quality: Pure gold has a distinct acoustic signature.
  • Malleability: Pure gold is a very soft metal and will dent easily. A gold-plated item and fake gold items will be harder because they have been crafted from tougher base metal.
  • Use a magnet: Gold is not attracted to a magnet; a reaction indicates iron is present.
  • Check the hallmark: Are the assay marks clear and from a country you trust? On real gold, a hallmark should clearly show the year and location of the assay test center. Consult reference books to confirm that you have a genuine hallmark. Be aware that on older or well-worn pieces, the hallmark may be illegible or missing.
  • Carry out an assay test: Genuine gold does not react with nitric acid. A lesser metal or fake gold will foam or dissolve when a drop of nitric acid is applied. Wear protective clothing as you are handling acid.
  • 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."
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Read More From Bellatory

How much is your jewelry worth? A gold assay test can reveal its value.

How much is your jewelry worth? A gold assay test can reveal its value.

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 jewelry 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.

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

  • 24 carat: 99.9% pure gold. It is highly valuable but very soft and not usually used to make fine jewellery.
  • 22 carat: 91.6% pure gold. Also very soft, so not ideal for stone set jewellery. It is used for plain gold jewellery, such as wedding bands.
  • 18 carat: 75% gold and contains metal alloys for strength and color. White metals are added to create white gold. Copper is added to create rose gold.
  • 14 carat: It contains just 58.5% gold content which makes it more affordable.
  • 9 carat: 37.5% gold has a high percentage of other metals, making it stronger and cheaper to buy.

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.

Selling Old Gold and Silver

The resale value of old gold and silver is subject to demand and supply. The more people who want to sell, the lower the price offered by dealers. However, not all gold buyers are the same, and you can select where and to whom you sell.

Imagine this scenario. You’ve split up from your partner and want to sell your valuable engagement ring for closure. You say it’s valuable because you know how much your partner paid for it, but how much will a dealer actually give you for it?

The first thing to remember is that your fiancé paid retail price for the keepsake. Any offer you receive will be based on the wholesale price. The two valuations are worlds apart. How can you find out if the ring is as valuable as you think, and is it better to sell your jewelry online or in person?

How Are Precious Metals Valued?

The main factors determining the value of your old jewelry are the weight of the precious metal it contains (quantity) and its grade or karat (quality). It helps to have an idea of what your items are worth before you approach a dealer.

You can make an estimate of value at home with a specialist weighing scale and a jewelry testing kit. I use this digital pocket kitchen scale. It is designed to weigh jewelry and precious metals and is calibrated to 0.01-gram accuracy. However, it is also a multifunction scale and can be used for normal culinary measuring.

The hallmark on this 18 carat gold hunting pocket watch is inside the case lid.

The hallmark on this 18 carat gold hunting pocket watch is inside the case lid.

Sell Gold Jewelry Online or In-Person

With any kind of selling, you need to have your wits about you. There are unscrupulous traders online, just as there are on the high street. Take the precaution of getting comparative quotes. Check out reviews for the companies that you intend to use. If an offer sounds too good to be true, then it probably is.

Check These Out

  • How long has the company been trading? Be cautious if they have been trading for less than three years.
  • Are they accredited by a trade body? e.g., Better Business Bureau (BBB), Jewelers Board of Trade,
  • Read online reviews and ask friends and family. Online reviews are worth reading, but check to see the date of posting.
  • If an offer seems way too good, trust your instincts!

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.

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.

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