Most people when they think of Jewelry metals they automatically think of the big three--Gold, Silver and Platinum. As people become more Jewelry educated they start to ask questions about the different types of metals used. They are generally very pleased and curious when they find the vast selection of metals available for different pieces of Jewelry. In order to understand the metals you must first learn the history of metals, what they comprise of and how they are best utilized. All a part of being an informed and educated consumer.
According to the dictionary, metal is any class of elementary substance characterized by opacity, ductility, conductivity, and malleability such as is found in gold, silver, platinum, copper, zinc, tin, nickel, etc. All of these metals, referred to as elements, are peculiar in that they are basically pure. When an elemental metal is combined with any other metal, the combination is defined as an "alloy". The platinum family includes five other elements, namely, rhodium, palladium, osmium, iridium and ruthenium. These elements are constituents of a natural alloy found only in platinum.
Element metals in their pure state except silver, are seldom used for jewelry and other decorative metalcrafts. Blended in various combinations, they form important alloys. Such metals and alloys are classified as ferrous and nonferrous. Ferrous metal refers mainly to iron, the primary alloy being steel, and the nonferrous metals indicate a complete absence of iron and are classified as "Precious Metals": gold, silver, platinum; Base metals---copper, zinc, nickel, aluminum, lead; alloy metals---karat gold, sterling silver, gold solder, silver solder, brass, bronze, pewter, nickel silver, and duraluminum.
Each pure metal and alloy has individual characteristics of color, hardness, ductility, malleability, and melting point and requires different heat treatment methods. Alloys are generally more desirable than their individual constituents. They are often either harder, heavier, more dense, or all of these when combined.
Pure gold and fine silver are too soft for some kinds of jewelry and must be alloyed to produce a harder metal so that they will be longer wearing, hold their shape better, and take a higher polish.
The addition of alloying metals to pure gold produces a different weight for each karat (k) alloy. Gold alloyed with copper will result in a lighter alloy and when alloyed with platinum, a heavier alloy. Karat gold alloys vary because of the different percentages of combining metals. Manufacturers order alloys from refiners to meet particular requirements such as a hard alloy to produce a smooth, hard surface when cast; an extremely ductile alloy that can be drawn extensively without breaking, or an alloy that will need to be age-hardened after shaping. All of these characteristics are possible with various alloys of the same karat content. Generally, the metal offered by suppliers is the best all-around alloy for use by the craftsman.
Alloys consist of two metals in combination, such as sterling silver (silver and copper), are called binary alloys. A combination of three metals---gold, silver, and copper--that forms 14-karat gold, is a ternary alloy. A four metal combination is called a quarternary alloy, and a five metal combination is a quinary alloy.
It is not practical for the craftsman to attempt to alloy metals, as one cannot be assured of a completely homogeneous mass, and the price of rolling mills is financially unfeasible for home workshops.
Metal Characteristics and Quality:
The metalsmith must be familiar with the basic properties, characteristics, and inherent qualities of the various metals he uses, which consist of malleability, ductility, tensile strength, fusibility, brittleness, and elasticity.
Malleability is the quality that allows the metal to be worked easily by hammering or pressure without crumbling. Gold is the most malleable metal, silver is second, and copper third.
Ductility is the quality of a metal such as is inherent in gold, wherein one ounce of pure gold can be drawn into a fine wire fifty miles long. Ductility and malleability are similar qualities, but some malleable metals, such as lead, cannot be drawn into wire by any means.
Tensile strength is the degree of tenacity that enables a metal when worked to withstand longitudinal stress without cracking. The tensile strength is measured by the minimum amount of longitudinal stress required to rupture the metal.
Fusibality refers to the capability of a metal to be combined with other metals to produce alloys. All elements and alloys become liquid when heated at different degrees of temperature, and return to a solid stage as they cool, or "freeze". Mercury, the one exception to this, remains a liquid at room temperature, becoming an absolute solid only when it reaches a temperature of minus 40 degrees F.
Brittleness, the opposite of ductility, indicates sudden breaking without warning. With some exceptions, very hard metals are usually brittle.
Elasticity is the ability of a metal to return to its original form when the force applied to change it has been removed.
How does a Jeweler Choose a metal?
The first step after creating a design suitable for a certain metal is to determine the thickness of the metal. Heavier metals, although malleable and ductile, are more difficult to work. In addition, heavy metals used for jewelry will tend to sag, and bracelets, rings, and pendants will be uncomfortable to wear. The thinnest metal that will hold its shape without bending when handled or worn is always preferable. Most jewelry is constructed of 14-24 gauge metals. Only precious metals should be used in objects that will be worn next to the skin, though other metals can be used if a protective precious metal backing is used.
Gold is the King of Metals. Its bright yellow glitter has made it, since the dawn of history, the metal par excellence. The earliest craftsmen used gold to fashion decorative pieces of all kinds . In the Middle Ages most craftsmen were trained as goldsmiths to create jewelry and ornaments of the highest order, some surpassing that done by craftsmen today.
Gold found in its native state is rarely pure 24 k, but it is usually associated with silver and often with mercury. When the silver content is a high percentage of the native gold mass, the metal is called "electrum", a natural alloy. Gold is also found in tellurides and ore containing quartz wherein it is either visable or enclosed in particles of sulfide minerals such as chalcopyrite, pyrrhotite, pyrite, and arsenopyrite. IN some high-production gold mines, the gold is not visible and can be seen only when viewed through a high powered microscope.
Gold has no oxides and is not affected by oxygen in the atmosphere as are other metals. Chloride of gold is formed when the metal is attacked by aqua regia (4 parts hydrochloric acid to 1 part nitric acid).
Gold is malleable to the point that it can be hammered into a leaf or sheet of foil 3/1,000,000 inch thick with an area approximately 6 square feet. The thin sheet is translucent and transmits a greenish light through the leaf.
When gold is alloyed, its ductility is diminished, but its malleability remains constant, except when large percentages of copper are added to the alloy. Nickel used in a white gold alloy has the same characteristics as silver. Zinc is added to the white gold alloy and lightens the color, but amounts in greater percentage than 14 per cent of the entire alloyed mass will change the color to red and make the alloy brittle. The reason for using zinc in gold alloys is to absorb the oxygen to prevent silver and copper oxides in the mix. Cheap "gold" jewelry is an alloy of copper and zinc with no trace of gold in the alloy. Any karat gold is called solid gold to distinguish it from gold-filled metals.
Skin discolorization by gold:
Gold darkens the skin because of either skin secretions or perspirationm which contains chlorides and often, sulfides that, coming into contact with the copper and silver molecules in a gold alloy, form a dark-colored salts, either copper sulfate or silver chloride.
The seacoast and semitropical areas produce chlorides. These salts combine with the salts produced thru perspiration to form a corrosive element that discolors the skin. The corrosive salts, when rubbed, turn into a smudge. Smog fumes filled with particles of silver dioxide and phosphate gradually attack jewelry and are evident as tarnish that rubs off on the skin. Eighteen-karat gold does not produce a smudge, as easily as 14 kt, and changing to white gold or pallidium will usually eliminate the problem entirely.
Karat Content of Gold:
The karat content and the color desired should be determined before alloying gold with other metals. Red or pink gold contains large percentages of copper and a small amount of silver; green gold is usually 14 kt or 18 kt gold alloyed with additional silver, or with silver that has a small percentage of copper; white gold is primarily 75 percent gold and the balance nickel, or both nickel and zinc. Gold alloyed with silver alone will be less hard and a lighter yellow color.
Copper alone added to gold makes the pure gold harder and more difficult to work; therefore, some percentages of copper and silver are usually combined in the alloy. White gold- formerly made of an alloy consisting of gold, silver, and / or palladium (from the platinum family)- is now also alloyed with nickel, copper, and zinc to produce more ideal melting characteristics.
A superior white gold and 10 percent palladium. Palau, containing 80 percent percent pure gold and 20 percent palladium, is a platinum substitute (not of lesser quality) for chemical laboratory utensils.
Gold quality is determined by karat content or fineness and each karat is 1/24th part. Pure gold is 24 karats, and as it is alloyed with other metals the karat content decreases so that 18 kt is 18 parts pure gold and 6 parts of alloy metals; 14 kt gold is 14 parts pure gold and 10 parts metals. The calculation for changing the alloy to different karat designation, either increasing or decreasing the pure gold content, is important.
The term "gold-filled" indicates the process wherein two thin gold sheets with a supporting piece of core metal such as nickel (approximately 1 inch thick) is placed between to form a sandwich, and then laminated with a brazing alloy into one inseparable sheet. After the fused ingot is made, it is placed in a rolling mill and rolled out to the required thickness. Gold-filled identification requires that the filling process must have been accomplished mechanically.
Gold filled articles stamped-"10k fine" indicate that the gold content of the sandwich is at lest 1/20th of the total metal content by weight. Lesser amounts of thinner sheets of gold may be clad with the core metal but only if so marked. Thinner gold sheets equal to 1/40th of the total metal weight would be stamped "1/40-14k" depending upon the karat of gold used in the outer sheets.
Stamping metals with karat content:
Gold articles must be stamped according to karat content. Severe federal penalties are imposed for misrepresentation. In addition to the karat content stamp, a hallmark (the craftsman's own insignia) should also be affixed in an obscure place on the inside or underside of the article. Articles so stamped with karat content indicate that all the metal used is equal to that karat marking. The alloy cannot deviate more than 1/2 karat in the entire piece, which includes findings and solder. Articles of various metal combinations are not stamped according to karat quality.
Silver, also called fine (pure) wilver, is the queen of metals and like gold and copper, is versatile metal with thousands of different uses. In addition to its use in jewelry and decorative objects, it is an important electroplating metal. The manufacture of photographic film is dependant upon silver, and its use in dentistry is equally important. Other uses of silver include ecclesiastical and domestic plate, buttons buckles, boxes, weapons, horse trappings, etc.
Silver has been held in high esteem through the centuries. Silver hallmarks came into use in 1300 A.D. and Sheffield plate, an innovation of the eighteenth century, gave birth to an important plating industry which still flourishes in the US and in England.
Formerly used for coinage, its value has increased as much as its demand for other uses. Silver is still worked as a native craft in Mexico, Thailand, the Southwestern US and Peru.
Silver occurs in the ore as a metal associated with other metals, especially gold. When it occurs as a constituent of large percentage on a natural gold/silver alloy, the metal is called electrum. It is usually a by-product of large mines producing gold, argentiferous lead, zinc, and copper ores, but it is also found in cobalt and nickel, and in lead and copper ores. It is also a prominent constituent in gold tellurides.
In malleability and ductility, fine silver is second only to gold. When melted its color is milky white and a milky pink. Harder than gold but not as hard as copper, it is used in its pure state-fine silver; however, it is more often used as an alloy-sterling silver. Fine silver is used in articles where a higher melting point is desirable, and it is especially useful for enameling projects because of the absence of oxides formed by copper in alloys. Silver foil, used like gold foil, can be rolled or hammered to a translucent sheet measuring 0.000012 inches, which is so thin that a blue light can be transmitted through the metal.
The standard alloy of sterling silver is composed of .925 parts pure silver and .075 parts pure copper. Mexican silver is alloyed with .950 parts silver and the remainder copper. Prior to 1965, US coin silver was .900 parts silver and the balance copper. Both types of silver are subject to oxidation when heated, however in normal atmospheric conditions, the silver alloy reacts much sooner than the pure metal. The normal oxide occurring on the metal when heated is a sulfide film produced by the torch. Silver alloys also produce oxides, cupric and cuprous, formed by the presence of copper in the alloy. Tarnish on silver is produced by sulfuric oxides in the atmosphere and by certain foods and body salts.
Platinum, rhodium, palladium--- three of the six seperate elements in the platinum family---are used for jewelry and decorative purposes. Platinum was in use for several centuries B.C. but a process to make it more malleable was not discovered until 1804.
The color of the metal is grayish white and resembles highly polished silver or white gold when finished. It is reasonably malleable and extremely ductile. The metal is softened with small percentages of silver or copper and is hardened when alloyed with iridium.
Like other metals, platinum work hardens and must be annealed to soften it to a malleable state. The metal does not oxidize when exposed to the atmosphere. A long wearing heavy metal, it has a melting point of 3223 degrees F. It is attacked by aqua regia, but no other acids.
Rhodium is resistant to oxidation and impervious to any acid or other solution. It is used almost exclusively for electroplating process's to ensure a permanent brilliance and long wearing durability. It's melting point is 3560 degrees F.
Osmium and Iridium:
These are separate elements but they are also found in a natural alloy called osmiridium. Iridium is a silvery-white metal that is quite hard, brittle, and the second heaviest metal known. Osmium is a bluish white metal and is one of the heaviest substances known. It is associated with iridium in alloys as already mentioned.
This is the sixth member of the platinum family, and it is very hard. It resembles osmium but is has no commercial importance.
Copper is the oldest known metal. It is presumed to have been discovered as early the 8,000 B.C. Three thousand years later it was alloyed with other metals, which initiated the Bronze Age. Copper occurs in a native state also as a sulfide, carbonate, and oxide to produce in combination over 360 different minerals. It is a yellowish red metal turning to a lemon color when heated. The melting point of copper is 1979 degrees F. The metal is affected by nitric acid and slightly affected by sulfuric acid, is easily worked, and when work-hardened is restored to softness by annealing.
Nickel was first discovered in 1751. One of its major uses was alloying with copper for coinage in many countries. Nickel is associated with copper nickel and iron sulfide ores, and is not found in a native state. It is the hardest of common metals. When it is refined, it is highly malleable and ductile metal that can be forged, cast, machined or worked by almost any method. It is used for electroplating and to produce an anticorrosive surface. Its melting point is 2651 degrees F. When cool, it is slightly yellowish and when hot is a salmon color. It work-hardens and must be annealed and cooled slowly to prevent stress.
Pewter used in early New England was shipped to the US from England the chief Pewter center, either already fabricated, or as stock metal to be worked by colony craftsmen. It encompasses two metal alloys, both called Pewter. The alloy known simply as pewter consists of 65-80 percent tin and 20-35 percent lead. The one most used by contemporary metalsmiths is called Brittania metal and is alloyed of tin (92 %), antimony (5%), and copper (3 %), with no lead. It is excellent for all types of forging and wrought work, for spinning, casting, etching, appliqué metal overlay, chasing and hand engraving.
Pewter is extremely malleable, does not work-harden, and is not ductile due to the lead content. Because of the low melting point of pewter (490 degrees F), it must be soldered with a soft solder having a much lower melting point ranging from 360 to 420 degrees F.
Food vessels formed of pewter require a high tin content, otherwise the alloy will produce lead crystals as the molten metal cools. These crystals mixed with food acids will corrode the metal, contaminate food, and cause lead poisoning. ( a very common ailment for colonial America).