JEWELRY GUIDE



art guide
Last Updated: April 2009

PRECIOUS METALS

Perhaps the most important part of a piece of jewellery is the metal that it is made of. Gold, platinum and silver are the precious metals of choice when it comes to setting and moulding jewellery. The properties of all three of these metals vary, thereby varying the value of the final piece of jewellery. The metals can be used simply as a setting for gems, or they can be fashioned into complete jewellery themselves and without any gems.

Gold
Exactly when and where gold was first discovered is difficult to assert with certainty. Deposits of the metal in its raw form are scattered across the globe, and gold was "discovered" repeatedly by people in different parts of the world in ancient times. Archaeologists surmise that the use of gold originated with the beginning of the earliest known civilisations.

That it is a very valuable metal has been known for millennia, but gold was first used as money in approximately 560 B.C. in the form of gold coins. One of the earliest known gold treasures unearthed was the "Gold of Troy" dating to the era 2450 -2600 B.C., excavated in Turkey. The largest collection of gold and jewellery was discovered in the tomb of Egyptian pharaoh Tutankhamen dating back to the second millennium B.C. Egypt was one of the richest countries in the millennia before Christ, which is evident from the vast amounts of gold ornaments and jewellery that has been discovered in the tombs of various pharaohs and queens.

Gold is widespread in the Earth's crust and is found in low concentrations in two different types of rocks. Reef Gold is found in metamorphous or igneous rocks, while Placer Gold is found in alluvial or placer deposits. The process of separating gold from these ores is known as extracting. Gold is a malleable and indestructible metal that is usually found in its pure form. It is one of the heaviest metals.

In 1992, the World Gold Council introduced the Gold Mark as an international identification mark for gold jewellery.

Yellow Gold: Gold without the presence of any alloys is in its natural colour and is known as yellow gold. It is measured in karats, denoted by the symbol "k". Pure gold is 24k and is extremely soft and malleable, thereby making it rare in jewellery. Gold of 20k, 18k and 14k are usually used to make jewellery.

The karat value of gold is reduced by mixing it with other metals, usually copper or silver. A higher karat value of the gold indicates a lesser percent of copper or silver is present in the alloy. 24k is 100% pure gold, 18k is 75% pure gold and 14k is 58.3% pure gold. 24k gold has a hardness of 2.5 on the Mohs scale. Gold tends to get harder as the karatage decreases due to the increased presence of other metals in the alloy. However, the value of the gold also decreases along with its karatage.

White Gold: In the 1920s, white gold was created as a common substitute for platinum in jewellery. White gold is an alloy of gold mixed with white metals such as silver, palladium, or nickel. Some jewellery made with white gold is coated with either rhodium or a palladium and platinum mixture, both of which are highly reflective and add lustre to the jewellery's surface. The mixture also hides the natural colour of white gold, which is a combination of slightly grey and slightly yellow. White gold is becoming increasingly popular in jewellery as it is less expensive than platinum for buyers that desire a "white" metal.

In addition to creating white gold, yellow gold can also be mixed with other metals to create alloys of rose gold, black gold and purple gold, among others. Varying the colour of the gold can also alter its physical characteristics, such as hardness and strength. As the karatage of the gold is lowered, a wider variation in colour can be obtained.

Platinum
In recent decades, platinum has become widely accepted as the precious metal of choice in high end jewellery. The metals properties and scarcity make it one of the most sought after elements in the world and ideal for jewellery.

The most valuable of the precious metals used in jewellery, platinum is also the newest. Although its presence was detected as early as 700 B.C., and Indians in pre-Colombian South America made platinum and gold jewellery in 100 B.C., the value of the metal was not realised until centuries later. Platinum came to be known to modern societies with the Spanish conquest of the "New World" in the 15th and 16th centuries. However, the Spanish did not think very highly of the metal because it hindered their gold mining activities and was resistant to melting. The Spanish named the metal "platina" or "little silver", from which it derived its modern name platinum. In 1751, Swedish scientist Scheffer discovered that platinum only dissolved in aqua regia, a highly corrosive substance, and categorised it as a precious metal.

Platinum was discovered to be malleable only when purified to its purest form in 1789 by French physicist P.F. Chabaneau. Over the next fifteen years, various chemists discovered palladium, rhodium and iridium, which are part of the platinum group of metals and are frequently utilised in platinum alloys that are used in jewellery. Platinum began to be used to make fine jewellery at the beginning of the 20th century when high temperature jewellers' torches were developed.

Platinum in Jewellery: Pure platinum is harder than pure gold or pure silver, yet it too soft for use in jewellery and must be alloyed with other metals to increase its hardness. Most platinum jewellery comprises 85 to 95% platinum combined with other metals. Several of the platinum family metals such as palladium, rhodium or iridium can be used in platinum alloys and are chosen based upon purity, casting behaviour, workability and reactivity. The most frequently occurring platinum alloy for the purpose of making jewellery is platinum-palladium. It is more durable than gold and silver yet requires to be alloyed to prevent bending.

Platinum hallmarks usually indicate the amounts of platinum and other metals present in the alloy expressed in parts per thousand. A hallmark of 900ppt denotes 90% platinum and 10% other metals.

Another advantage to the use of platinum in jewellery is its low reactivity when compared with extraneous agents. Unlike silver, platinum does not tarnish even after prolonged contact with sulphur oxides. Unlike gold, it is not adversely affected by chlorine, bleach, or detergents. It is also an excellent metal to use for setting stones as the smallest and slightest amount of platinum will retain its shape and is resistant to breakage, also making it a popular choice for jewellery makers as they can be more innovative with the designs that they fashion. Claw settings and filigree too can be created out of platinum without concerns about durability.

In addition to the properties that make it ideal for jewellery, platinum is also extremely rare and therefore very valuable. To make a single platinum ring requires approximately two tonnes of ore to be mined to obtain enough of the metal. Platinum deposits are primarily found in Russia, South Africa and Canada, but demand far exceeds supply and platinum is thus an expensive metal. In Japan, platinum jewellery is very popular and is known as hakkin or white gold.

Silver
Silver is possibly the precious metal with the widest variety of uses. From electricity to photography and jewellery to artefacts, silver can be found in several different forms in both the modern and the ancient worlds.

Silver was discovered after gold and copper in approximately 4000 B.C., and it is believed that the first major source of mined silver was the region of Anatolia or modern Turkey. Silver was most widely traded in the Asia Minor region at the time. In approximately 2500 B.C., the Chaldeans adopted more efficient and advanced methods of extracting silver from ores with a process known as 'cupellation'. With the passage of time, the Laurium mines near the Greek city of Athens became the major production hub for silver in Europe. These were silver-lead deposits and were actively mined for six centuries from 500 B.C. to 100 A.D. The Laurium mines were the largest individual source of silver production in the world for almost a millennium. Silver was also produced to a smaller extent in Asia Minor, Sardinia, and Asia.

After the Laurium mines' production began to diminish, the Spanish mines emerged as a major source for silver. Between 750 and 1200, silver mines were also discovered in the Schemnitz, Rammelsburg, Goslar, and Saxony regions of Germany. But it was the discovery of the 'New World' in 1492 that opened the doors to the Central and South American silver mines. Between 1500 and 1800, the mines of Mexico, Peru and Bolivia produced 85% of the world's silver, while the remaining 15% was obtained from Germany, Hungary, Russia, Chile and Japan, among other countries. In the mid-19th century, a large silver deposit was discovered in Nevada, USA, which emerged one of the largest producers of silver worldwide. Today, Central and South America retain their status as the largest silver producers in the world.

Properties and Alloys: Pure silver is a complicated metal to work with. It is extremely malleable and ductile, making it easy to mould into different shapes and for different uses. It also has a low boiling point, making it easy to cast into different shapes. However, it is also very susceptible to pressure and is easily dented, rendering it impractical for use in everyday objects such as jewellery and household artefacts.

Silver also reacts with chemicals such as the sulphur compounds that are present in the atmosphere, which render the normally luminous metal dull and discolour objects made of silver.

To make silver more suitable for use in jewellery, it is mixed with other metals to form alloys. There are two types of silver alloys � Britannia Silver, which is at least 95% pure silver, and Sterling Silver, which is at least 92.5% pure silver. Sterling silver is typically used in jewellery. The remaining 7.5% of the alloy is most commonly comprised of copper, which adds hardness to the silver. However, copper also increases the ability of the silver to tarnish, and therefore sterling silver jewellery must be properly stored and cleaned to retain its shine. The presence of copper in the alloy does not diminish the value of the metal. The price of silver is generally determined by its weight, the labour and skill involved, and the complexity of the jewellery's design. Sterling silver jewellery is extremely affordable when compared to white gold or platinum.