There is no clear definition of noble metals, but most metals regarded as noble have the following properties to some extend:

- They are durable. They are not easily destroyed or poluted by other chemical substances. Noble metals are also chemically inert, and do not easily go into composition with other elements. That means that they are resistant to corrotion and oxydation.

- Because noble metals are chemically inert, those are found free in nature in metallic form. Only few other metals are found in metallic form in nature. The first metals people knew abotwas actually were noble metals, like gold, silver, platinum, and semi-noble mtals like copper.

- The chemical inertness of noble metals makes most of the them unpoisonous. Therefore adorns made of such metals do not generally irritate the body and they can even be used inside the body to repair injuries or imperfections or for other medical purposes. The most prominent example is fillings in tooth cavities made of gold or artificial gold teeth.

- They have a fine splendour or a fine colour.

- They do not easily brittle or crack.

- It is easy to form objects from them.

- Noble metals have are highly electrically conductive. The good ability to lead electric current and the inertness making that ability stable, make them valuable as conductors in tiny electronic devices. Thin deposits of gold are for example important conductive elements in microprocessors and other logically processing electronic units.

- They are rare, so that the prize is high. The rareness also gives an experience that is something else than the ordinary days experience when you look at it. They will also be expensive.

Metals having these properties are gold, platinum, silver, tantalium, palladium and rhodium.

Many noble metals, however, are very soft, so they must be alloyed with other noble metals or semi-noble metals to be hard enough. Gold for exaple must be alloyed with copper or silver.

Gold was probably the first metal known to human beeings. It is not extremely difficult to find, but you generally find very small amounts of it. Probably gold was originally found in sandy bottoms of streams as small balls. Later people learned to wash the gold out of the sand to accumulte porsions of some significance.

Gold, and the term "Karat" (Also spelled carat).
Gold has the hardness of 2,5 on Mohs scale, which makes objects of pure silver weak to deformation by mechanical forces. Gold is therefore mostly not used in a pure condition, but is alloyed by other metals, espesially copper, silver, nickel, zink, palladium or platinum to make it stronger and give the metal some special color. The more copper and gold in the alloy, the more yellow or redish it wil look. The more silver, the whiter the alloy will get.

The term "karat" defines how purity a piece of gold is. One karat is defined as a 1/24 part, that is the same as 4.1667 percent. An usual used purity rate is 16 karat, that is 16/24 gold and 8/24 of another metal.



Silver and the term fineness
Silver is a blank metal with very high ability to reflect light and clean silver therefore looks very brilliant. Silver has some tendency to get a layer of oxid or hydoxid that reduce the brilliance. Silver has the hardness of 2,5 on Mohs scale, which makes objects of pure silver weak to deformation by mechanical forces. Therefore silver is alloyed to other metals to heighten its strengths, or to make spesial color apparances.

The purity of silver is expressed by the term "finenes" that measures how many 1/1000 of silver there is in a piece of the metal. Usual silver alloys are sterling silver containing 92.5 percent of silver and 7.5 percent of another metal, usually copper, and Jewelry silver containing 80 percent silver and 20 percent copper. Sterling silver thus has the fineness of 925 and jewelry silver is then 800 fine.


Platinum
Platinum is a white metal as silver. It does not reflect light as well as clean silver and is therefore not fully as brilliant in appearance. But silver easily gets a layer of oxid or hydroxid that reduces the brilliance. Therefore platinum may practically appear more lustrious. It is very rare, actually 20 times more rare than gold. It is also extremely resistant against corrotion and very heavy. A volume of platinum weights the double of the same volume of gold. Platinum has a hardenss of 3,5 on Mohs scale and one can therefore make durable objects of pure platinum. It has a high melting point, but it can easily be formed by hammering or forging. Platinum is used in its pure form without being alloyed, wich is not practical to do with silver or gold.

Base Metal
Base metals are any metals that are non-precious. Gold-colored base metals include brass and bronze alloys. Silver-colored base metals include white bronze, lead, zinc, nickel, tin and steel. Copper and bronze (the brown type) are also considered base metals. Base metal is often plated with precious metals (i.e.. gold-plated and sterling silver-plated).

Gauge
The thickness of a piece of wire or sheet metal is referred to as its gauge. The higher the number the thinner the wire. An earring wire that is 24 gauge is thus thinner than one of  22 gauge.

Gold-filled
Gold-filled doesn't means that the piece of metal is filled with gold. Actually, a the gold layer is covering a core of base metal. The base metal is also something yellow-colored, often brass.

There are two types of gold-filled products on the market: 14/20 and 12/20. In a 14/20 the gold layer is 14 karat and this constitutes 20 % of the whole metal piece. In a 12/20, a 12 karat gold layer costitute 20 % of the whole piece.

14/20 gold filled is the most popular combination because most people are not allergic to 14 karat gold.