Gold, Silver & Platinum: A Brief Overview
by Alex White
Metals can be really fascinating...finding out what you can do with them, how they react, creating your own physical objects from raw materials. Working with metals is challenging, fun and sometimes frustrating, but worth the effort because of things you can create with them -- useful things, decorative things, and things to wear, like jewelry and hair ornaments.
Pure metals are extracted as ores, meaning they are elements of the Periodic Table. Other metals are alloys, which are metals composed of two or more of the pure metals.
The two main groups of metals are ferrous and nonferrous. Ferrous is from the Latin ferrum, iron. So those in the ferrous category all have iron in them. They include the pure iron and many alloys, such as the many different alloys that are labelled types of gt6steel.
Nonferrous metals, which do not contain iron, fall into three subgroups: precious metals, base metals and alloys. The precious metals you know already, platinum, gold and silver. The base metals are copper, aluminum, lead, tin, nickel and zinc. And finally, the alloys are metals that combine ores within and between these two groups. Such alloys are brass, bronze, pewter, nickel silver (which, by the way, contains no silver), sterling silver and karat gold.
Gold is a lustrous yellow metal. In its natural state, it is too soft for most purposes. Therefore, gold is almost always alloyed with base metals to give it strength. Karat golds are alloys of gold. The higher the karat number, the higher amount of pure gold there is in the alloy.
The melting point of gold is 1945.4oF, 1063oC, facts to file away in your trivia folder, although it is an important piece of knowledge for a jeweler. Gold is naturally found as placer gold in alluvial riverbed soil, as flakes grains or nuggets, or as reef gold, which is gold embedded in a solid matrix of quartz or other rock.
Gold surpasses all other metals in its malleability and ductility. A metal that is more malleable is more easily worked. A metal with high ductility is easily drawn into wire forms or hammered thin in sheet forms. Gold is resisant to ordinary solvents and corrosion, which is why gold found in ancient ruins is usually well-preserved.
As an alloy for jewelry, gold can be combined with copper, silver, nickel and zinc. Each of these alloying metals gives the resulting alloy a particular character and color. Adding platinum or palladium results in white gold, while the addition of more copper to a yellow gold produces a reddish color, often called rose gold.
The karat of an alloy refers specifically to the relative purity of the gold. Pure gold is 24k. The spot price for gold, once around $300 per ounce, has about quadrupled, so that referring to something or someone as "worth its weight in gold" is high praise indeed.
Silver is the precious metal for the rest of us. Recently, its preciousness has increased in the commodities market, along with that of gold and platinum. Several years ago, silver was selling for about five to six dollars per ounce. As early 2010, the spot price hovers around 18 dollars per ounce.
In its native form, silver appears in flakes, forms something like wire and massed forms, even, rarely, as large as 1500 pounds. Today, silver is a byproduct in the refinement of gold, lead, copper and zinc ores. The silver is recovered from these metals in the refining process or extracted from ores by various processes, such as smelting.
The melting point of silver is 1780.9oF, 960.5oC, which is lower than that of gold. Sterling silver melts at the slightly lower point of 1640oF, 893oC. Silver’s malleability and ductility run second only to gold. It is the whitest metal and polishes to a luster of high reflectivity, to the great chagrin of photographers of silver objects.
Like gold, silver’s pure form is too soft, and it is alloyed to harden the metal and increase durability. The most common alloy is, of course, sterling silver, which contains 92.5% fine silver and 7.5% copper. This is the origin of the phrase "925 Sterling Silver."
Unlike gold, silver tarnishes when exposed to sulphur, and given the sulphur in urban air, it’s impossible to prevent tarnish in fine silver or sterling silver. Warding it off is possible to some extent with anti-tarnish plastic bags, strips or blocks, and polishing will restore the gleaming shine.
Tarnish-free sterling silver is more nearly possible with rhodium plating or the use of an alloy of sterling silver called Argentium®, which contains deoxidizers. However, freedom from tarnish usually costs a bit more.
And the spot price for platinum? Well over a thousand dollars per ounce. But it’s worth it if you can get it. This metal is hard and durable, does not tarnish, and is the jeweler’s choice for a setting for diamonds, beautifully setting off their white brilliance.
Platinum was rare until 1822, until large deposits were found in the Ural Mountains in Russia. A group of related rare or noble metals that are residues of platinum ore are osmium, iridium, palladium, rhodium and ruthenium.
As with gold, platinum is found in fine grains and nuggets in alluvial material, such as riverbed soil or rock. Platinum is also refined as a byproduct from nickel ores.
The jewelry market makes wide use of platinum because of its hardness, ductility, malleability and resistance to corrosion. In fact, this market accounts for 50% of the total production of platinum. Alloys with five or ten percent ruthenium or iridium are used since they are harder than pure platinum. The term 950 Platinum refers to an alloy of 95% platinum, and 900 Platinum to an alloy of 90% platinum.