How do we measure gold purity ? What means 18K, or 14K gold purity ? What's the difference between 18K and the hallmark 750 ?
Actually, gold purity is measured in karat, this weight unit originates from the Greek, and through the time has been transposed to measure gold purity : 1K represents 1/24 of pure gold. Therefore 24K means 100% pure gold, although absolute purity is never achieved, hence 24K is represented by the number 999, which means a purity of 99.9%.
18K stands for 18/24 parts of pure gold, in other words 18K means 75% of pure gold, and is represented by the number 750.
14K stands for 14/24 parts of pure gold, therefore a purity of 58% and is represented by the number 583 or 585.
A piece of jewelry made of 18K gold contains 75% of gold and 25% of other metals, mainly silver and copper. A mix of different metals is called an alloy.
A 18K gold alloy will always be made of 75% of gold and 25% of other metals, its composition will vary depending on the colour to be achieved.
A 18K alloy made of 75% of gold, 12.5% of silver and 12.5% of copper will be yellow.
Rose gold has a bigger proportion of copper (which is naturally red) in the remaining 25% dedicated to other metals, giving the rose or red colour to the alloy.
White gold is made by adding palladium to the remaining 25% to take over the yellow, and to make it greyish (see our post about Platinum).
The legal transcription of purity is the hallmark engraved on a bullion or a piece of jewelry. The international convention used is the parts of fine gold per 1000. Therefore 18K is translated by the number 750, or 750 parts per 1000. When a piece of jewelry is engraved with the number 750, it means it is in 18K. A bullion engraved with the number 999 means it is pure gold, or 24K.
In most countries, it is a legal obligation for the manufacturer to indicate the purity on the piece of jewelry, therefore never buy a piece of jewelry without the purity indication.
18K jewelry is the standard in the luxury jewelry market and finds its roots in Europe. While pure gold is too soft, 18K is hard enough to allow different shapes and designs, and brings a good resistance to scratches for every day use.
Asia, India, Africa or Middle East were mainly 22k or 24K markets although 18K is more and more popular among younger generations.
USA was historically a 14K jewelry market, for economic reasons, but has been moving progressively to 18k for the luxury segment of jewelry.
To cast a perfect 18K gold alloys requires a quiet sophisticated equipment and know how, in order to achieve perfect colour, brightness, stability and purity. ZEVA alloys are made on modern equipments with experimented technicians, and purity is continuously monitored by external independent laboratories.