The purity of gold is measured in karats. Pure gold measures 24 karats but is too soft in this state to be used effectively in jewelry. To increase its strength and durability, pure gold is alloyed with other metals such as silver, copper, and zinc, resulting in the different karats of gold. The most common mixtures are 18 karat (75% gold), 14 karat (58.5%), and 10 karat (41.7%). A higher karat indicates higher gold content, higher purity and higher value. Gold jewelry is usually stamped with the karat mark such as 18K, K18 or 750 for 18-karat gold, and14K, K14 or 585 for 14-karat gold.
Gold can take on a different hue depending on the metals added. The most popular colors of gold in jewelry are yellow, white, and rose. All colors of gold still contain the same amount of pure gold per karat.
YELLOW GOLD is a gold alloy that consists of pure gold, silver, and copper. This unique mixture gives yellow gold its distinct color.
ROSE GOLD is a mixture of pure gold, silver, and a higher percentage of copper, also known as pink or red gold. Although the names are often used interchangeably, the difference between red, rose, and pink gold is the copper content: the higher the copper content, the stronger the red coloration.
WHITE GOLD is comprised of pure gold mixed with white metals such as palladium, silver, zinc or nickel. The natural color of white gold tends to have a slight yellowish tint. That’s why most white gold jewelry is plated with rhodium. Rhodium is a durable precious metal which is a member of the Platinum Group Metals, often used to plate white gold and sterling silver jewelry for a long lasting sheen and a resistance to both scratching and tarnishing. Not only does rhodium plating gives the jewelry a bright white look with a mirror-like finish but it also increases the strength and durability of the metal itself. Over time the plating will wear off, exposing the true color of the metal.
Platinum is a rare precious metal which is naturally hypoallergenic and silver-white in color. It is lustrous, ductile, and malleable and has an excellent resistance to corrosion, oxidation and high temperature. Due to its high density, superior strength, and natural silver-white color, platinum has become an attractive choice for diamond settings.
Given that platinum is rarer and denser and has a higher melting point than gold – platinum melts at 1,768°C whereas gold at 1,064°C, it is more difficult and expensive to make jewelry with platinum than with gold. Platinum is often made into jewelry with a majority of its natural form and mixed with other platinum group metals to increase hardness and durability such as iridium, palladium, ruthenium, rhodium or osmium. The platinum standard is based on parts per thousand, where 1000 parts = 100%, and platinum jewelry is usually stamped with quality marks.
Pt950 or 950Pt means a composition of 950 parts platinum and 50 parts other metals.
Pt900 or 900pt means a composition of 900 parts platinum and 100 parts other metals.