People have made jewelry from every kind of metal. As new metals come available, like stainless steel and titanium, they too find their way into jewelry. However, since ancient times, three metals have stood out from all the others. These are the noble metals.
The noble metals have a few properties in common. They are precious and actually used as currency. They are found worldwide, but not in large quantities. The properties that encourage jewelry us are that they are easily worked and they resist corrosion. Of course, their popularity is based on emotional qualities as well. The noble metals are considered beautiful, sensuous, and glamorous.
These properties lend themselves to jewelry and the vast majority of our jewelry is set in gold, silver, platinum, or at least something that resembles them.
|Metallurgy Terms:Noble MetalsMetals that resists corrosion and oxidation.
A means of separating gold and silver from other metals and impurities. The ore is heated in a cupel, (a ceramic cup,) which absorbs the impurities.
Washing ore causes the heavier metals to stay behind where they can be recovered.
To surround a metal with a substance that will react with the metal under heat. Silver is parted from gold by cementation with salt.
Metals with a low boiling point, like mercury, are vaporized to separate them from other metals.
Purifying gold by mixing it with mercury.
To melt an ore to separate and refine the metals within it.
More than any other metal, gold has captivated the human psyche. Gold is rare, it is easily worked, it never tarnishes, and it is considered the most sensuous of metals.
No other metal is as workable as gold. An ounce can be stretched into a thread more than 50 miles long, or rolled into a 100 square foot sheet!
Gold lasts practically forever. Recent studies show that gold evolved in the far reaches of the universe billions of years ago and came to our planet in its infancy. It never oxidizes or corrodes and only a few rare acids and hot chlorine bleach will attack gold.
The yellow metal is reused extensively. Old coins and jewelry are refined to be used again. So, you never know where your gold came from. The metal in your ring may be newly mined, or some of it could be from ancient pieces.
In spite of its divine properties, gold has one significant drawback; it is soft and wears easily. Because of this, gold is usually alloyed, mixed with other metals, to make it stronger. Along with the added strength, a gold alloy changes other properties. Some alloys stain peoples skin or cause an allergy reaction. This has nothing to do with the gold, but the metals it is mixed with.
A variety of metals are used to alloy gold. People have added silver, copper, nickel, iron, zinc, tin, manganese, cadmium, and titanium to gold.
Regardless of the alloy used, they are always referred to as Karat Gold. Karat is a measurement of the fineness of gold. (It is not to be confused with carat, which is a measurement of weight.) One Karat is to 1/24th part of the whole. Pure gold is 24 karat. An alloy that is half gold and half other metals is 12 karat.
Gold is usually alloyed for strength, but in parts of Asia, pure 24 karat gold is worn. In the US, 10 karat is the lowest alloy used and world wide, the British have the lowest alloy at 9 karats. A relatively new alloy is 99% gold and 1% titanium. This alloy is very close to pure gold in color and has greatly improved durability.
The color of gold changes with the alloy. Copper makes it a darker yellow. White gold is usually 10% to 20% nickel, plus zinc, copper, and often platinum or manganese. Contrary to popular belief, white gold contains no silver, which softens gold and gives it a green tint. Gold alloys also come in green, (which does contain silver,) red, and blue.
Laws regarding the purity of gold are very strict. In the US, gold must be within three parts per thousand of the karat marking for solid pieces; seven parts per thousand for soldered pieces. Unless you are speaking of 24 karat gold, it is illegal to use the terms gold or solid gold without specifying what karat it is. Laws in other countries are equally as restrictive.
New gold does not mean that it was recently mined. Instead, it means that it has been carefully refined to current standards. Old gold comes from melting previously used jewelry. Depending on the amount of solder in those pieces, it may be somewhat lower karat. The impurities cause bubbles and other headaches when cast. So, old gold is usually sent to a refiner, rather than being melted down at your local jeweler.
Gold solder is sold by its color, not by its gold content. The solder must have a lower melting point than the piece it is joining. This is achieved by mixing it with metals that have a lower melting temperature than gold. For an attractive finished piece, the solders are matched in color to the karat gold they are used with.
Less Than Solid Gold
To get the appearance of gold without the cost, jewelry is made with thin coats of gold on less expensive metals. Knowing the variations is crucial to both the jeweler and the consumer.
The term gold overlay applies to two methods, gold filled and rolled gold plate.
Gold filled pieces have 5% or more gold applied to a base metal. They are described by the amount of gold overlay and its karat. For example, a piece may be stamped 1/20 14K G.F. That means it has a 14 Karat gold layer that makes 1/20 of the weight.
Rolled gold plate is similar, but the gold can be as thin as 1/40 of the weight. It is also stamped by fineness and content, 1/40 14K RGP.
Gold platings are the thinnest and least expensive. The gold is a few thousandth of an inch thick at best. These wear off easily.
On all the above, you must exercise great care. You cannot take a filled piece to the polishing wheel. While it may be 1/5 gold overall, the layering gets thinner on the edges as it is worked. You can easily polish down to the base metal on the edges, ruining the piece.
This white metal has had an illustrious history, at times being more highly valued than gold. Long used as a medium of exchange, its name is synonymous with money. Today, silver has found many new uses including photography, batteries, auto glass defogger, magnetic strips, etc.
Its most outstanding feature is its luster. Silver will take a higher polish than any other metal. It has the singular drawback that it tarnishes. Metal smiths often use this feature to highlight certain design elements. Modern chemicals easily remove tarnish, but the fact remains that silver needs more care than the other precious metals.
Silver is more abundant and much less expensive than gold or platinum. This has a lot to do with its popularity. Some jewelry styles, like the Native American, rely strictly on silver.
Silver is more difficult to work than gold, because it conducts heat so well. Beginners often learn soldering on this less expensive metal. When they graduate to gold, they find it easier to control the heat.
Silver is also alloyed. Most common is Sterling meaning .92.5% with the rest usually copper.
Mexican Silver usually 95% silver and 5% copper.
Coin silver 90% silver, 10% copper by US standards.
Britannia Silver is at least 95.84% silver.
Other European alloys are 87.5%, 83% and 80% silver. Some South American silversmiths use an 80% allow that does not tarnish. The actual alloy should be stamped on the jewelry.
Electrum is a natural alloy of gold and silver. It was popular with the ancient Egyptians. Since it is in its natural form and not alloyed, the silver to gold ratio varies.
Niello is a black mixture of silver, copper, lead and sulfur. It is used to fill in designs. Is more like enamel than an alloy.
Nickel or German Silver are misnomers, as they have no silver in them at all. Instead, they are various alloys of nickel, zink and other metals with a silver appearance.
Quicksilver is an ancient term for mercury. Quick meaning alive, as in the quick and the dead.
Platinum is rarer and more expensive than gold. Its unsurpassed holding power and durability makes it a premium jewelry metal. This non-tarnishing, white metal is considered ideal for setting white diamonds.
Its use in jewelry is relatively modern. In the early 1900s, it became a symbol of wealth and celebrity status. Stars like Greta Garbo and Cole Porter appeared on film with platinum jewelry and accessories. It also became popular for setting exceptional gems. 530-carat Star of Africa diamond in British royal scepter is set in platinum.
The oldest record of platinum use is as an inlay in ancient Egypt. However, the Egyptians though it was a variation of electrum, (a natural blend of gold and silver.) Native Americans used it for centuries in small decorative objects. Platinum was unknown to Europeans until Spanish discovered it in Columbia. The Spanish called it platina, meaning little silver. It was not identified as a new metal until the 1700s.
Due to its high melting point, (1755 C, or 3190 F,) platinum would not yield to old-fashioned blowpipes unless combined with arsenic. This was extremely dangerous and the white metal did not become widely used until invention of oxyhydrogen torch in the mid 1800s.
Today, half of US and a quarter of all platinum worldwide is used for catalytic converters. (Catalytic means catalyst; it causes chemical reactions in other substances while remaining unchanged.) US Bureau of standards uses platinum for weights. Platinum never oxidizes, it remains the same forever.
Platinum is not a single metal, but a group of similar materials. The group includes platinum, iridium, palladium, ruthenium, rhodium, and osmium. Platinum is the most abundant. Rhodium is popular as a non-tarnishing plating for white gold, silver, and other platinum metals. All but osmium are used for jewelry.
The most common alloys include 90% platinum and 10% iridium, or 95% platinum and 5% ruthenium. Ruthenium makes for the harder and stronger alloy.