The word Gold used by itself means all gold and refers to pure gold meaning 24 karat gold. Because 24 karat gold is soft it's usually mixed with other metals called alloys to increase its hardness and durability. If a piece of jewelry is not 24 karat gold the karat quality should accompany any claim that the particular item is gold.The karat quality marking tell you what proportion of gold was mixed with the other metals. Fourteen karat (14kt) jewelry contains 14 parts of gold mixed with 10 parts of an alloy metal. The higher the karat rating the higher the proportion of gold in the piece of jewelry.

Jewelry should be marked with its karat quality. Near the karat quality mark you also should see the name or the US registered trademark of the company that will stand behind the mark. The trademark maybe in the form of a name, symbol or initials. If you don't see a trademark accompanying the quality mark on a piece of jewelry look for another piece.You will find that markings reveal to an extent the region where the item is intended to be sold. For example, India and China culturally wear 22kt and 24kt jewelry, the UK is famous for selling 9kt pieces, North America tends to sell 10kt and 14kt whereas South Americans prefer to wear 18kt.  

Platinum is a type of brushed metal that used to cost more than gold. It is usually mixed with other similar metals known as the platinum group: iridium, palladium, ruthenium, rhodium and osmium. Different markings are used on platinum jewelry as well, the more platinum the higher the number on the mark. The quality markings for platinum are based on parts per thousand. For example, the marketing 900 platinum means that 900 parts out of 1000 are pure platinum, or in other words, the item is 90% platinum and 10% other metals. The abbreviation for platinum is PLAT or PT and this will be placed in the marking with its corresponding value.

The words silver or sterling silver describe a product that contains 92.5% silver. Silver products sometimes maybe marked .925 which means that 95 parts per thousand are pure silver.
Some jewelry may be described as silver-plate: a layer of silver is bonded to a base metal. Marks in silver are used for compounds that contain 90% silver. According to the law, quality marked silver must bear the name of a US registered trademark of the company or person that will stand behind the mark. In different parts of the world you will find several silver marks lower than .925 and this will simply mean that those items contain a lower percentage of pure silver and more of metal alloys.