What is gold?

Gold  is one of the most expensive metals on Earth. The melting point of gold is 1063.4°C. It is so soft and supple in the processing, that one ounce is enough for making a five-kilometer wire or a thin sheet with an area of one hundred square feet (9.3 sq. km.)

Gold is one of the rarest metals found in nature; and as well as pure gold does not rust, it can be called an eternal metal. An interesting fact: gold is present almost everywhere - in the Earth's crust, in the seas and rivers, but it is very difficult and very expensive to get it. To produce one ounce of gold, two and a half to three tons of ore have to be processed. The content of gold in the earth's crust is very low - 3 mg/kg, but fields and sectors, highly rich in this metal, are very numerous. Gold is contained also in the water. 1 l of sea, as well as river water contains about 4x10 (-9) g of gold.

Today it is the most popular metal used in the manufacturing of jewelry. But because pure gold is very soft, other metals are usually added to it to make it more solid and hard to bend.

If there is a mixture of two or more metals, the final product is called alloy. Gold used in jewelry is basically an alloy (metals added to gold are also called "alloys").

What is a karat (kt)?

British karat system. Traditionally, the purity of gold is measured in British karats. 1 British karat is equal to one twenty-fourth of the mass of the alloy. 24-karat gold (24K) is clean and free of any alloys.

To change the quality characteristics of gold, for a variety of purposes (eg, to increase hardness); alloys are made with different compositions. For example, 18-karat gold (18K) means that the alloy contains 18 parts of gold and 6 parts of other metals.

The Russian system of assay marks. Adopted in Russia, the system is different from the international one. In Russia, the purity of gold is measured by assay.
The assay mark ranges from 0 to 1000 and shows the gold content in thousandths. For instance, 18-karat gold matches 750 assay mark. Gold with an assay mark of 999.96  is considered "substantially pure”; gold bars have such fineness of metal. Gold with 999.99 assay mark is expensive to obtain and is only used in chemistry.

In the Russian jewelry industry it is permitted to manufacture jewelry using gold with assay marks 375, 500, 585, 750, 900, 958 and 999.

U.S. labeling	Content of pure gold in the "%"	EU marked (sample)
24k 22k 20k 19k 18k 15k 14k 12k 10k 9k	100 91,6 83,0 79,2 75,0 62,5 58,3 50,0 41,7 37,5	1000 916 833 792 750 625 585 500 417 375

Color of gold.

Pure gold is always yellow. But as pure gold is too soft for most jewelry products and must be fused with other metals in order to increase its hardness, the color of the alloy may vary depending on the amount of alloying metals. Jewelry gold is usually mixed with copper, zinc, silver, nickel, platinum or palladium. The color of the metal depends on what kind of metal is used as an alloy.

Color alloy	Au (gold)	Ag (silver)	Cu (copper)	Pd (palladium)
yellow pink white pale yellow-green yellowish yellow pink orange red	75% 75% 75% 58,5% 58,5% 58,5% 58,5% 33,3% 33,3%	17% 12,5% 5% 38,25% 28% 18,75% 9,0% 53,4% 9,5%	8% 12,5% – 3,25% 13,5% 22,75% 32,5% 13,3% 57,2%	– – 20% – – – – – –