| |
|
|
| |
 |
| Alloys |
|
| An alloy is a mixture of two or more metals fused together in molten state. Metals when melted tend to dissolve in one another forming alloys. The various properties of a metal like malleability, ductility, strength, hardness, resistance to corrosion and appearance can be improved by mixing with other metals. Alloys have properties different from its constituents. |
| |
|
 |
| |
 |
| |
|
| |
 |
| |
 |
 |
 |
| |
|
| |
 |
 |
| |
| |
| Amalgams |
| |
| Amalgams are special alloys that combine mercury and other metals in the periodic table. The amalgam of Hg, Ag and Zn is used in dental fillings. A solution of sodium metal in liquid mercury metal is called sodium amalgam. Zn amalgam is used in voltaic cells. |
| |
|
| |
| From the first discoveries of gold in ancient times, its beauty and the ease with which it could be worked inspired craftsmen to create it into ornaments, not just for adornment, but as symbols of wealth and power. The skills of the goldsmith from ancient Egypt to Benvenuto Cellini or Carl Faberge still amaze us. As Pihder wrote nearly 2,500 years ago, "Gold is the child of Zeus, neither moth nor rust devoureth it". Today, gold jewellery is more a mass- market product, although in many countries still treasured as a basic form of saving. jewellery fabrication is the crucial cornerstone of the gold market, annually consuming all gold that is newly mined. |
| |
| Pure gold is used in those parts of the world where jewellery is purchased as much for in- vestment as it is for adornment, but it tends to be vulnerable to scratching. Elsewhere, it is usually mixed, or alloyed, with other metals. Not only do they harden it, but influence the colour; white shades are achieved by alloying gold with silver, nickel or palladium; red alloys contain mainly copper. A harder alloy is made by adding nickel or a tiny percentage of titanium. |
| |
| The proportion of gold in jewellery is measured on the carat (or karat) scale. The word carat comes from the carob seed, which was originally used to balance scales in Oriental bazaars. Pure gold is designated 24 carat, which compares with the "fineness" by which bar gold is defined. |
| |
 |
| |
| The most widely used alloys for jewellery in Europe are 18 and 14 carat, although 9 carat is popular in Britain. Portugal has a unique designation of 19.2 carats. In the United States 14 carat predominates, with some 10 carat. In the Middle East, India and South East Asia, jewellery is traditionally 22 carat (sometimes even 23 carat). In China, Hong Kong and some other parts of Asia, "chuk kam" or pure gold jewellery of 990 fineness (almost 24 carat) is popular. In many countries the law requires that every item of gold jewellery is clearly stamped with its caratage. This is often controlled through hallmarking, a system which originated in London at Goldsmiths' Hall in the 14th century. Today it is compulsory in such countries as Britain, France, the Netherlands, Morocco, Egypt, and Bahrain. Where there is no compulsory marking manufacturers themselves usually stamp the jewellery both with their own individual identifying mark and the caratage or fineness. |
| |
|
|
| |
|
|
| |
|
|
|
