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For some people, it's all about the gold. For others, precious metal is simply a gemstone delivery device. Either way, precious metals are an integral part of fine jewellery. The right metal can enhance the beauty of a coloured gemstone, or disguise the slight tint of a diamond.
Gold was one of the first known metals and may have been one of the first metals used for ornamentation and decoration. It has been valued as a precious commodity for thousands of years, used as money and a vehicle for storing wealth in many cultures. Today, gold is still valued as a basic for of saving in many countries, but the expanding global jewellery market annually consumes all newly-mined gold.
Gold will not tarnish or rust, and is the most malleable of all metals. Pure gold is too soft for daily use, so it is alloyed with other metals to give it strength and durability. Gold is naturally yellow, but the colour can be altered by the type and percentage of alloy used. Copper gives rose gold its warm, pinkish colour, and certain percentages of silver alloy can produce a greenish tint. White gold is alloyed with silver, nickel or palladium. Because this produces a metal that still has a yellowish tint, almost all white gold is plated with rhodium to enhance the whiteness. Over time this rhodium plating may wear off, revealing the original metal colour. Re-plating is a simple process that can be done to restore your jewellery's whiteness if needed.
Karat or Carat?
Both carat and karat are derived from the word for the carob seed, which were used as measurements of weight in Oriental markets. However, when used in reference to gold, carat is a measure of purity. In the United States, the designation for gold fineness is always karat, but in other parts of the world, the terms carat and karat are used interchangeably when referring to gold purity. The weight of gold in jewellery is measured in grams.
Karatage is expressed in 24ths. 24k gold is 100% gold with no alloyed metals; 18k gold is an alloy of 18 parts gold and six parts other metal. The most widely used alloys for jewellery in Europe are 18 and 14, although 9 is popular in the UK. In the United States, most fine jewellery is 18 karat, but 14k is the most popular, followed by 10k. The table below gives the various karatages and their equivalent gold content in percent or in fineness terms as recognised by international standards.
|Definition of Caratage in Gold Content For Recognised International Standards
Source: World Gold Council
Many countries require every item of gold jewellery be clearly stamped with its karatage. This is often controlled through hallmarking, a system that originated in London at Goldsmiths' Hall in the 14th century. In the UK today, there are three compulsory hallmarks applied to precious metals as a quality control: a sponsor's (maker's) mark, a fineness mark, and an assay office mark. These marks establish the origin and fineness of the precious metal and ensures it has been accurately and independently tested (assayed.) In the United States, the Federal Trade Commission does not require a gold fineness stamp; however, if one is used, it must be accompanied by the manufacturer's mark.
Platinum has been used for ornamentation for thousands of years, but wasn't identified scientifically until 1735 after the Spanish conquistadors found it in the Rio Pinto in Colombia, South America. Thinking it was unripe silver, they dubbed the metal "platina" or "little silver" and tossed it back into the river. Platinum wasn't widely used in jewellery until a torch was invented in the late 1800s that was hot enough to allow the average jeweller to work the dense metal. It continued to gain popularity until 14kt white gold was introduced as a more affordable alternative. Platinum was still the metal of choice for wedding rings until World War II, when it was declared a strategic metal by the US government and banned for use in jewellery until after the war.
Platinum is 30 times rarer than gold. There is just one platinum mine for every 10 gold mines. It has been estimated that if all the platinum existing in the world were poured into an Olympic swimming pool, the depth would barely reach your ankles. By comparison, gold would fill up over 3 pools.
Purity is expressed in parts of pure platinum per 1000, so that 1000 parts equals 100% purity. Most platinum jewellery is 95% pure platinum and only 5% other metal. Platinum is a member of a group of six metals known as the PGM (platinum group metals) several of which are used as alloys. As with gold, allowable tolerances and marking requirements vary from country to country.
|Common Platinum Quality Marks
Source: Platinum Guild International USA
The UK recognizes 999, 950, 900 and 850 standards for platinum, and requires the same three hallmarks for platinum as for gold: a fineness mark, a sponsor's mark, and an assay office mark.
The US FTC Platinum Guide for marking jewellery states that any piece made of 950 parts or more per thousand of Pure Platinum can be marked “Platinum.” Platinum with 850 to 950 parts per thousand can be marked in accordance with international standards of “900 Pt.” or “850 Plat.” Pieces with a minimum of 500 parts per thousand Pure Platinum and at least 950 parts per thousand Platinum Group Metals in total, must be marked with the parts per thousand of Pure Platinum, followed by the parts per thousand of each Platinum Group Metal. Example: “600 Plat 350 Irid.” Pieces with less than 500 parts per thousand pure platinum cannot be marked with the word platinum or any abbreviation thereof.
Purity & Hallmarks
There are other alloys for silver, but sterling silver is the standard for beautiful high-quality silver jewellery. Like platinum, silver fineness is measured in parts per 1000. Sterling silver is an alloy containing 92.5% by weight of silver and 7.5% by weight of other metals, usually copper. A number of new tarnish-resistant alloys, such as Argentium sterling silver, have appeared in recent years, but no one alloy has emerged to replace copper as the industry standard. Pure silver is very soft, but some jewellery is made of 999% "fine" silver, which is less susceptible to tarnish than sterling. Silver that is 900% pure is called coin silver, and there is even an 800% alloy that is sometimes used for jewellery.
International hallmarking regulations for sterling silver are similar to those for other precious metals.
Palladium is the lightest of the Platinum Group Metals. The fact that it is 40% lighter in weight than platinum allows for much thicker mountings without them becoming uncomfortably heavy. It is 12.6% harder than platinum, making it even more durable. Surface wear is easily restored by professional cleaning and re-polishing. Palladium is naturally whiter than even platinum and, unlike white gold, does not require rhodium plating to retain its whiteness. Like platinum, palladium is a pure metal which makes it hypoallergenic. Also, palladium costs less than either platinum or white gold.
Long offered as an affordable alternative metal for class rings, palladium is beginning to be seen again in fine jewellery. Look for more palladium jewellery as manufacturers and designers discover the beauty, versatility and affordability of palladium settings.
Purity & Hallmarks
Palladium purity is measured in parts per 1000 by weight, as is platinum. UK requires a hallmark on all palladium articles (subject to certain exemptions) if they are to be described as being partly or wholly made of palladium. The three standards recognized are 999, 950 and 500 parts pure palladium by weight per 1000. It is expected that 950 will be the most common standard.
-By Cynthia B. Reuschel