Downscaling pure gold (24-karat) to 22-karat, 18-karat, 14-karat, or 9-karat gold isn’t as difficult as you would think it is. It’s a process called alloying, wherein you add other metals to gold to make it more durable and harder. This is because gold is incredibly soft on its own, almost like chewing gum. Goldsmiths add other metals to gold to increase its hardness and make it more suitable for use in jewellery.

Karat level measures how pure gold is. 24-karat gold is 99.9% pure gold, 18-karat is 75% pure, 14-karat is 58.3% pure, and 9-karat gold is 37.5% pure. In 18-karat gold, the other 25% is a mixture of alloys.

To downscale gold’s karat level, you’ll have to dilute it with an alloy. Essentially, you’ll need to melt it in a crucible, add alloys, then pour it into a mould and wait for it to cool.

What’s an Alloy?

In chemistry, an alloy is a mixture of two or more elements, one of which must be a metal. Metals used in alloying gold include copper, nickel, zinc, silver, or brass.

Note: this article is a general overview of alloying. If you don’t consult with a goldsmith, you risk damaging your gold or creating dangerous substances.

How to Alloy 24K Gold into 22K, 18K, 14K, or 9K Gold

First, decide what ratio you would like and the metal. Remember that the metals you use will determine the gold’s colour.

  • Copper will add a reddish tint and create rose gold.  For example, 18K rose gold is typically made with 75% gold and around 25% copper.
  • Silver creates green gold or electrum.
  • Nickel creates a silvery-white appearance but is less used because it’s a common allergen.
  • Palladium or Platinum creates white gold with a greyish hue. It’s hypoallergenic.
  • Zinc creates yellow gold.
  • Iron creates a blueish hue.
  • Aluminium makes a purplish gold, though it’s often brittle.

Most people opt for copper, zinc or silver. Choose the ratio of alloy to gold depending on how soft you would like your jewellery to be and how rust-resistant you want it. The higher the alloy amount, the more susceptible to rust the gold will be. The higher the gold volume, the softer the metal will be. Most fine jewellery strikes a balance between 18-karats and 14-karats, though 10-karats is also acceptable.

Remember that 24-karat gold means it’s 24 parts of 24 parts gold. 18-karat gold is gold that’s 18 parts gold, 6 parts alloy. 14-karat gold is 14 parts gold, 10 parts alloy, and so on.

Step 1: Calculate Fine Gold Content

To understand how much alloy you should add, you must calculate its fine gold content. Identify your gold’s karat level. You’ll need to multiply the total weight of your gold item by the fraction representing its karat level.

The formula goes: fine gold content = total weight x (karat level / 24)

For instance, if you have 22-karat gold that weighs 500 grams, its fine gold content would be worked out as:

Fine gold content = 500 x (22/24). Its fine content is 458.33 grams. 

Then, subtract the fine gold content weight from its total weight to identify its alloy weight.

500g – 458.33g = alloy weight of 41.67 grams.

Step 2: Determine Additional Alloy Needed

To lower your gold’s current karat level to the one you would like, you’ll need to find out how much additional alloy you’ll need.

Multiply the fine gold content by the fraction representing your target karat’s alloy ratio. The formula goes.

Let’s say you want to lower 22-karat gold to 14-karat gold. The formula would go:

Desired Alloy Weight = Fine Gold Content x (10/14)

Previously, we determined our 22-karat gold’s fine gold weight is 458.33 grams.

Our formula would go:

Desired alloy weight = 458.33 grams x (10/14)

Desired alloy weight= 327.38 grams (rounded)

Then, subtract the existing alloy weight from the desired alloy weight to determine how much more alloy to add.

In our example, we determined our 22-karat gold has 41.67 grams of alloy in it. So, we’d subtract 41.67 from 327.38. We would need to add 285.71 grams more alloy to make 14-karat gold.

Step 3: Decide on Alloy Composition

Your alloy composition will influence your gold’s karat level and colour. For a paler yellow, use equal parts copper and silver. For a standard yellow gold, use more copper than silver, generally 6 parts copper to 1 part silver.

If you’re going to cast your gold, use brass, copper, and zinc. Brass and zinc will work together to produce a yellow-gold colour and mitigate air bubbles by reducing oxygen content. It also helps it flow into moulds better.

Copper is a critical component of alloying gold for casting. It adds strength, colour, and optimises gold’s behaviour during casting. To avoid having to work out specific ratios, we recommend buying commercially available alloys, which are designed to enhance strength and durability without significantly affecting gold’s signature colour.

Calculate Alloy Weights

Calculate how much of each alloy you’ll use depending on ratios.

In our example, we’re going to aim to get a standard yellow-gold, using the ratio of 1 part silver, 3 parts copper, and 3 parts brass. We’re aiming for an alloy weight of 285.71 grams, and will use:

  • 40.82 grams of silver
  • 122.45 grams of copper
  • 122.45 grams of brass

Then, we’ll melt the gold and alloy mix together in a crucible, maintaining a constant temperature and mixing thoroughly. Gold and its alloys have similar melting points, usually around 1050 to 1100 degrees Celsius.

After you’ve melted your gold and alloys together, pour it into a desired mould.

Ta-dah! You’ve reduced the karat level in your gold.

Let Us Do the Hard Work for You

If you would like to reduce the karat level of your gold without worrying about alloy ratios and buying a crucible, contact Gold and Diamond Traders. We’re a family-run business that specialises in bespoke jewellery creation, gold handling, and diamonds.

Let us do the hard work for you and help you create a piece you love.