One of the prominent features of gold is flexibility, which makes it hard to produce various exquisite patterns and styles, in particular, pearl, stone and jade set on gold jewelry are likely to lose.
For this reason, it’s a common practice of jewelry makers to add traces of Ag, Cu, Zn and like metals in gold jewelry for additional strength and toughness, gold jewelry produced in this way is also called K gold jewelry.
K gold jewelry can be custom-made in various colors. Internationally popular K gold jewelry is available in various colors, of which most common varieties are yellow and white. Adding Pd or Ni in 25% gold will make white gold, of which gold is the main composition, and which is called white K gold jewelry.
With current level of scientific and technological development, it’s impossible to refine gold material of 100% purity. Therefore, in marked gold products, gold content is indicated by standard gold karats, and pure gold is generally called 24K gold, which means 100% gold content in theory, but it does not exist in reality. Thus, no gold content of gold jewelry is allowed to be marked as “24K gold” in a nonstandard way according to national standard currently in force. Since pure gold is marked as 24K gold, i.e. 100% gold content in theory, 1K gold represents 1/24 gold content in gold products, approximately 4.16%. 18K gold represents gold content of 18/24, equal to 75% gold content, with remaining impurities such as Ag or Cu.
It’s said that “gold can’t be hundred percent pure”, generally, gold jewelry contains less than 1% of other metal(s). Express criteria are set out in national standard for the purity of gold content in gold products, that the dealer must tag each piece of gold jewelry, clearly indicating its gold content and count of karats. The count of karats of all gold jewelries must be calculated according to national legal unit of measurement. The gold content should be marked with “K gold” (24K gold not included), “gold” (Gold content not less than 99%) or “pure gold” (Gold content not less than 99.9%), nonstandard tagging like “99.99% pure gold”, “pure gold”,”24K gold” and “9999 gold” are not allowed.
When we say 24kt or 24k Gold jewelry, we mean that all the 24 parts in the gold are just pure gold without traces of any other metal(s) or 99.9 percent pure. When we say 22kt or 22k Gold Jewelry we mean that 22 parts of the jewelry, is gold and the balance 2 parts are some other metal(s) or equal to 91.3 percent gold plus 8.6 percent of some other metal alloy When we say 18Kt or 18k Gold Jewelry, we mean that 18 parts of the jewelry is gold and the balance 6 parts is some other metal or equal to about 75 percent gold plus 25 percent of some other metal alloy We can roughly state that each Karat is equal to approximately 4.1625 percent. The difference of the other metal or alloys of the metal, gives the jewelry its hardness and color. We can state that 24 Karat is the softest and 10 karat the hardest, because 10kt would have 41.6 percent gold and the balance would be other metals which are mostly harder than gold.. The color from the other metals enhances the beauty of the jewelry as the case may be, white gold, yellow gold, red gold etc.
Pure 24 karat gold is Yellow in color, when the purity is lowered, by adding different alloys, the color of the gold can be changed to reflect the color of the alloy. i.e. if we were to convert 24k gold to 22k gold we would be adding about 8.4% alloy, which would now make it 91.6 percent pure (22 karat). The addition of alloy has various purposes, one is to give it hardness, to make the gold jewelry stronger, as pure gold is very soft, the other would be to change the color, e.g. if copper would be added to alloy then the gold would appear reddish, instead of the yellow or if any of the white metal was added to the alloy it would make it appear white. This is not to be confused with the finishing, which are just on the top surface of the jewelry, which are mostly different types of hand paints or coatings, used like paint on the surface to enhance just the look, e.g. to give it an antique look, underneath the paint or coating, it would be solid yellow gold