Jewellery facts
Jewellery is a fascinating subject and has been an important part of culture for thousands of years. From the earliest day's when precious stones and metals were simply found in riverbeds to the commercial operations that span the globe, and centres that specialise in grading, cutting and polishing - it remains one of the most exciting markets. If you work within retail or one of the specialist areas of the business you will relieve full training in all aspects of Jewellery. For now, here is a broad insight into the dynamic world of some of the more common precious jewels and metals.
Gold is the most malleable and ductile metal; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent and readily forms alloys with many other metals. These alloys can be produced to increase the hardness or to create exotic colours. Native gold contains usually eight to ten percent silver, but often much more. As the amount of silver increases, the colour becomes whiter and the specific gravity becomes lower.
Gold has been known and highly-valued since prehistoric times. It may have been the first metal used by humans and was valued for ornamentation and rituals. Egyptian hieroglyphs from as early as 2600 BC describe gold, which king Tushratta of the Mitanni claimed was "more plentiful than dirt". Egypt and Nubia had the resources to make them major gold-producing areas for much of history. Gold is also mentioned several times in the Old Testament, and the south-east corner of the Black Sea was famed for its gold. Exploitation is said to date from the time of Midas, and this gold was important in the establishment of what is probably the world's earliest coinage in Lydia between 643 and 630 BC.
Although the price of some platinum group metals can be much higher, gold has long been considered the most desirable of precious metals, and its value has been used as the standard for many currencies (known as the gold standard) in history. Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties.
Because of the softness of pure (24k) gold, it is usually alloyed with base metals for use in jewellery, altering its hardness and ductility, melting point, colour and other properties. Alloys with lower "k", typically 22k, 18k, 14k or 10k, contain higher percentages of copper, silver or other base metals in the alloy. Copper is the most commonly used base metal, yielding a redder metal. Eighteen carat gold containing 25% copper is found in antique and Russian jewelry and has a distinct, though not dominant, copper cast, creating rose gold. Fourteen carat gold-copper alloy is nearly identical in colour to certain bronze alloys, and both may be used to produce police and other badges. Blue gold can be made by alloying with iron and purple gold can be made by alloying with aluminum, although rarely done except in specialized jewelry. Fourteen and eighteen carat gold alloys with silver alone appear greenish-yellow and are referred to as green gold. White gold alloys can be made with palladium or nickel.
Gold in antiquity was relatively easy to obtain geologically; however, 75% of all gold ever produced has been extracted since 1910. It has been estimated that all the gold in the world that has ever been refined would form a single cube 20 m square.
Silver is a very ductile and malleable (slightly harder than gold) metal with a brilliant white metallic lustre that can take a high degree of polish. It has the highest electrical conductivity of all metals, even higher than copper.Among metals, pure silver has the highest thermal conductivity (only the non-metal diamond's is higher), whitest colour, the highest optical reflectivity and is a poor reflector of ultraviolet light. Silver also has the lowest contact resistance of any metal.
A major use of silver is as a precious metal. Jewellery and silverware are traditionally made from Sterling silver (Standard silver) an alloy of 92.5% silver with 7.5% copper. Sterling silver is harder than pure silver, and has a lower melting point. Britannia silver is an alternative hallmark-quality standard containing 95.8% silver, often used to make silver tableware and wrought plate. Silver is used in medals, denoting second place. Some high end musical instruments are made from sterling silver, such as the flute.
The name of the United Kingdom monetary unit "pound" reflects the fact that it originally represented the value of one troy pound of sterling silver. Silver has been coined to produce money since 700 BC by the Lydians, in the form of electrum. Later, silver was refined and coined in its pure form. The words for "silver" and "money" are the same in at least 14 languages.
Its germicidal effects make silver utensils valued, and increase its value as jewelry.
When pure, the metal appears greyish-white and firm. The metal is corrosion-resistant. Platinum's wear- and tarnish-resistance characteristics are well suited for making fine jewellery. Platinum is more precious than gold. The price of platinum changes along with its availability, but its price is normally slightly less than twice that of gold. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king. Naturally- occurring platinum and platinum-rich alloys have been known for a long time. Though the metal was used by pre-Columbian Native Americans, the first European reference to platinum appears in 1557. The word platinum comes from the Spanish word platina, meaning "little silver."
Due to its rarity, greater difficulty to work with and the need to alloy it with (at the time) an even more expensive metal iridium, platinum was only used in a limited way in jewelry at the end of the 19th century. This changed at beginning of the 20th century when most diamond ring mountings and most exclusive jewelry were almost completely made of platinum.
A diamond is a transparent crystal of tetrahedrally bonded carbon atoms and is the hardest natural material known to man. About 130 million carats (26,000 kg) are mined annually, with a total value of nearly USD $9 billion. The name diamond derives from the ancient Greek adamas "invincible". They have been treasured as gemstones since their use as religious icons in ancient India and usage in engraving tools dates to early human history. Popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy and innovative and successful advertising campaigns. They are commonly judged by the "four Cs": carat, clarity, colour and cut.
Roughly 49% of diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil and Australia. They are mined from kimberlite and lamproite volcanic pipes, which brought to the surface the diamond crystals from deep in the Earth where high pressure and temperature enables the formation of the crystals.
The hardest diamonds in the world are from the New England area in New South Wales, Australia. These diamonds are generally small, perfect to semi perfect octahedra and are used to polish other diamonds. Their hardness is considered to be a product of the crystal growth form, which is a single stage growth crystal.
Unlike many other gems, they are well suited to daily wear because of their resistance to scratching - perhaps contributing to their popularity as the preferred gem in an engagement ring or wedding ring, which are often worn every day.
Ruby is a red gemstone that varies from a light pink to a blood red, a variety of the mineral corundum.
The colour is caused mainly by chromium and its name comes from ruber, Latin for red. Natural rubies are exceptionally rare, but synthetic rubies (sometimes called created ruby) can be manufactured fairly cheaply.
Rubies are mined in Africa, Asia, Australia, Greenland, Madagascar and North Carolina. They are most often found in Myanmar (Burma), Sri Lanka, Kenya, Madagascar and Cambodia. Historically, the Mogok Valley in Upper Myanmar produced some of the finest rubies but, in recent years, very few good rubies have been found there. The unique colour in Myanmar (Burmese) rubies is described as "pigeon's blood", they are known in the trade as "Mogok" rubies and the latest ruby deposit to be found in Myanmar is situated in Nam Ya. Sometimes spinels are found along with rubies in the same rocks and are mistaken for rubies. However, fine red spinels may approach the average ruby in value.
Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness - among natural gems only diamonds are harder (Mohs 10.0 by definition). All natural rubies have imperfections in them, including colour impurities and inclusions of rutile needles known as "silk".
Gemmologists use these needle inclusions found in natural rubies to distinguish them from synthetics, stimulants, or substitutes. Almost all rubies today are treated in some form (of which heat treatment is the most common practice) and rubies which are completely untreated and still of excellent quality command a large premium. In general we can list the following types of improvements: colour alteration, improving transparency by dissolving rutile inclusions, healing of fractures or even completely filling them.
The price of rubies is primarily determined by colour. After colour follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions will indicate the stone has been treated one way or another. Cut and carat also determine the price.
Sapphire is the single-crystal form of aluminium oxide, a mineral known as corundum. It can be found naturally as a gemstone or manufactured in large crystal boules for varied applications, including infrared optical components, watch faces, high-durability windows and wafers for the deposition of semiconductors such as GaN nanorods.
The corundum group consists of pure aluminium oxide. Trace amounts of other elements such as iron, titanium and chromium give sapphires their blue, yellow, pink, purple, orange or greenish colour. Sapphire includes any gemstone quality varieties of the mineral corundum, except the fully saturated red variety, which is instead known as ruby. Although blue is considered the normal colour for sapphire, it is found in the full range of spectral colours as well as brown, grey and black. Those other than blue in colour are considered fancy colour sapphires.
Various shades of blue (dark and light) result from titanium and iron substitutions in the aluminium oxide crystal lattice. Some stones are not well saturated and show tones of grey. It is common to bake natural sapphires to improve colour and this is usually done by heating the sapphires to temperatures of up to 1800°C for several hours or by heating in a nitrogen deficient atmosphere oven for 7 days or more.
Purple sapphires are lower in price than blue ones, these stones contain the trace element vanadium and come in a wide variety of shades. Yellow and green sapphires have traces of iron which gives them their colour. Pink sapphires have a trace element of chromium and the deeper the colour pink the higher the value as long as the colour is going toward the red of rubies. Sapphires also occur in shades of orange and brown and colourless sapphires are sometimes used as diamond substitutes in jewellery. Salmon colour padparadscha sapphires are orangy-pink, pinkish-orange or pink-orange in colour and often fetch higher prices than many of the finest blue sapphires.
Emerald is a variety of the mineral beryl, coloured green by trace amounts of chromium and sometimes vanadium.
It is highly prized as a gemstone and by weight is the most valuable gemstone in the world, although it is often made less so by inclusions, which all emeralds have to some degree.
Emeralds come in many shades of green and bluish green. There is a wide spectrum of clarity, dependent on the inclusions and fractures in the crystal and clear stones with dark yet vibrant colour command the highest prices.
Most emeralds are oiled as part of the post lapidary process in order to improve their clarity - cedar oil is often used, as it has a similar refractive index.
Emeralds in antiquity were mined by the Egyptians and in Austria, as well as Swat in northern Pakistan. A rare type of emerald known as a trapiche emerald is also occasionally found in the mines of Colombia. A trapiche emerald exhibits a "star" pattern, it has ray-like spokes of dark carbon impurities that give the emerald a six-pointed radial pattern. Colombian emeralds are generally the most prized due to their transparency and fire. Some of the rarest emeralds come from three main emerald mining areas in Colombia: Muzo, Coscuez, and Chivor. Fine emeralds are also found in other countries, such as Zambia, Brazil, Zimbabwe, Madagascar, Pakistan, India, Afghanistan and Russia. The value of an emerald depends on cut, colour, clarity and carat.