You’ve probably heard of yellow, red and white gold, but did you know gold also comes in green, purple and black? Read on to find out more about what causes these colours in gold.
If you’ve read my previous post you know that pure gold (a.k.a 24K or 999) has a rich nearly orange yellow colour. However gold rarely occurs in nature in pure form. It generally grows as a crystal structure including other elements, like silver or copper.
As early explorers traveled around the world and found gold in different places, they realized not all gold is the same colour. Some early finds of gold were a metal known a Electrum – a mix of gold and silver with a pale slightly greenish colour. Other finds showed gold with a reddish tinge.
Later medieval alchemists set out to artificially create gold and they discovered through much experimentation that it was possible to change the colour of gold by adding different metals. For example when they added copper it made a somewhat brittle metal that work-hardened very quickly and had a red hue. In contrast adding silver left the metal very malleable and created a pale metal with a green tinge. Eventually they discovered that mixing copper and silver produced a yellow metal, albeit a lighter shade, with good working properties.
So when we talk about coloured gold we are really talking about the blend of other metals or alloys that are added to pure 24K gold. Some goldsmiths have specialised processes for making a variety of colours – the recipes for which are safely guarded trade secrets. In this Post I’ll talk about the most common gold colours and their compositions.
No matter what the purity, be it 18K, 14K or 9k, the process starts with gathering the correct amount of pure metals and blending them to create different colours.
For example, if we want to make yellow gold we use a mix of 50% silver and 50% copper to add to 24k pure gold. The higher the gold content the richer the yellow colour: 18k yellow has a rich buttery colour, whereas 14k yellow has a straw yellow colour and 9k yellow is a pale yellow.
The “recipe” for making 2 grams of 14k yellow gold (enough to make a slim wedding band) looks something like this:
- 1.2 grams of 24K gold casting grain
- 0.4 grams of 999 silver casting grain
- 0.4 grams of 999 silver casting grain
To change the colour of gold we simply change the proportions of the other metals or alloy as shown here:
To make red gold we eliminate the silver and add only copper. The higher the gold content the less obvious the colour: 18k red gold has a warm yellow colour, 14k red gold has a salmon-pink colour, and 9k red gold can look quite coppery as seen in Antique jewellery in the UK. To mitigate the red colour and make pink or rose gold alloys we can add in a little bit of silver.
Green Gold or Electrum
A colour you may not have heard of before is green gold. Green gold is a mix of gold and silver, with trace amounts of other metals. It has been found to form naturally as far back as 600 BC, when it was used for the first metal coins ever made. Ancient Electrum was a bright, nearly white metal with a slight greenish tinge as its gold content was relatively low (45-55%).
As an experiment I made some 14k green gold, using just gold and silver, but found it too soft to be practical. I added a tiny bit of copper (less than 5%) which made the colour more intense and also made the metal stronger – success!
Use of yellow, green and red gold goes back to antiquity, but white gold is relatively new. The first attempts at making white gold were made in the early 1700’s The metal we know as white gold now was developed in the 1920’s as a cheaper alternative to platinum, which was popular in Art-Deco diamond jewellery.
To make white gold we add a blend of only white metals, like silver and palladium (a member of the platinum family). White gold isn’t really white, it is just paler than yellow gold but with a grey tinge. 18k white gold looks pretty similar to 14k yellow, 14k white gold is more grey with a touch of yellow and 9k white gold can have a nearly aluminium like appearance.
So why does white gold on the high street all look the same, no matter what the purity?
To get that bright white finish, white gold jewellery is usually rhodium plated. Rhodium is another metal in the platinum family. The rhodium plated jewellery looks great on display, but the plating does tend to wear over time exposing the underlying yellow-grey material.
There is a growing trend among goldsmiths and designer/makers to design pieces with the natural material in mind. Why? Well
- It feels more honest – what you see is what you get
- It is lower maintenance – no need to re-plate the piece further down the line
- It removes a time consuming and costly step from the making process – advantages that benefit you as a customer.
Is there a price difference between the different colours of gold?
Where there is a price difference depending on the gold purity – eg. the buttery yellow 18k gold is more expensive than straw yellow 14k and there is another step down for the pale yellow 9k gold – there is generally no difference between red or yellow gold in the same karat proportion. So 18k yellow gold is generally the same price as 18k red gold – you are after all getting the same amount of gold and the gold content is what sets the price.
The exception is white gold. The palladium that is mixed into the white gold is part of the platinum family and is a more expensive metal than silver and copper. As a result white gold is generally slightly more expensive than yellow or red gold. In many cases, there is also additional cost of rhodium plating the finished piece of jewellery.
Are there other colours of gold?
Yes, there are more possibilities, like black, blue and purple, but they are not really suitable for jewellery.
Black gold is the effect of oxidation of the “other metals” at the surface, rather than colouring the metal throughout. This and other methods of blackening gold are considered a surface treatment and tends to wear away over time, much like oxidized silver.
Purple and Blue gold do change the body colour of the metal throughout, but are notoriously brittle and impossible to work using traditional jewellery making techniques.
That said, metallurgists continue to work on developing new metals and experiment with applications so who knows what lies ahead.