Precious metals are essentially the noble metals, which are characterized by being durable, malleable, non-oxidizing metals that are well suited for use in the manufacturing of jewelry. Other characteristics that are commonly associated with precious metals are that they are strong, they polish well, and can maintain that polished, shiny look over time with little or no maintenance. These metals, because of those properties, and because of their relative scarcity, are valued in cultures around the world, and almost universally command premium prices. The metals that one usually thinks of when considering precious metals are typically gold, silver and platinum, and in fact, they are the precious metals. And while gold, silver, and platinum are the main categories, there are many, many variations…alloys…of these metals. The platinum group alone has six varieties, several of which are routinely used in the jewelry industry. There are also some relative newcomers into the jewelry world, which although not actually precious metals, are quite exotic and worthy of mention.
Makers Mark, Quality Mark, and Purity…Oh my!!!
Oh my indeed…because this can become very confusing. But here’s how it works:
On October 1, 1981, Volume 15, Section 295 of the United States Code of Federal Regulations became effective, which is commonly known as the National Gold and Silver Marking Act. This Act provided for more stringent standards regarding the actual fineness of gold imported, exported, or transported through interstate commerce, as well as the hallmarking requirements. In short, this Act requires that any gold that falls within the above criteria, must be within 3/1000 parts of the marked purity, (as long as no solder is involved). [Note: when solder has been used, 7/1000 parts is allowed]. In English, this means that, using 14kt gold as an example, (which is 0.5833 parts pure), any item stamped with a 14kt stamp can not be less than 0.580 parts gold. It is important to note that a quality mark was NOT required by this Act. Therefore, a manufacturer is not required to put a fineness/quality mark on an item, but if a quality mark IS used, a “makers mark”, (or hallmark), MUST be used. Clear??? So I don’t have to put a “14kt” stamp on a jewelry item, but if I do, then I also must put my makers-mark/hallmark on it as well. The hallmark is required as a means of providing accountability for any stated fineness. A quality mark and a makers mark indicates that the manufacturer is representing the fineness of the gold and thus bears the responsibility of the accuracy of the purity of that gold. Thus, if an item is given a quality mark of say, 18kt, but does not have a makers mark on it, the distributor or end retailer will become responsible for the purity of the item if a discrepancy occurs.
Gold used in jewelry may be found in many different purities and in a variety of colors. Variations of both purity and color are the result of mixing various alloying metals with pure gold, in different combinations and concentrations to obtain different results in physical and mechanical properties. Purity is a measure of how much gold is in the gold. Purity is represented by karats, abbreviated by “kt”, as in 24kt, 14kt, etc. For example, gold that is marked as 24kt, is absolutely pure gold…100%. Gold this pure is not normally used for jewelry in the United States due to the fact that it is too soft and will deform easily. Gold marked as 14kt is approximately 50%, (or more precisely, 0.5833), gold and the rest is alloying metals. There are quite a few alloying elements used to vary the purity of pure gold, which produces a wide range of physical and mechanical properties that are quite different from pure gold. Those metals that are used to alloy with pure gold, are used in various combinations and concentrations and yield different properties to the gold base metal. Copper, nickel, zinc and silver are the most commonly used alloying agents with gold to make 18kt, 14kt, and 10kt gold. The following table illustrates the % gold vs the % alloy for various gold purities:
Gold Purity % Gold % Alloy
- 24 karat (24kt) 100 0
- 18 karat (18kt) 75 25
- 14 karat (14kt) 33 41.67
- 10 karat (10kt) 67 58.33
This shows that 14kt gold, the most widely used gold purity in the United States, is barely 50% actual gold! Other countries use different purities for their jewelry. It is common to find 9kt, 20kt, and 22kt gold in Europe and Asia.
Probably what comes to mind first when thinking about gold, as well as the most common type. It is typically alloyed with varying amounts of copper and zinc to achieve the desired hardness and durability for whatever end purity is wanted. The actual “yellowness” of the gold will depend on the purity and the alloys used.
Another very popular variation, is usually alloyed with nickel to achieve the “white” color. However, in reality, it has a slight yellow tint to it. This is because, so called “white gold” is actually yellow gold with alloys added that will help to give it a white look. Very often, in order to conceal this off-white, or yellow tint, a very thin coating of rhodium, (a member of the platinum group), will be used. This imparts a nice pure white look to the gold alloy, but because it is very thin, will wear off over time and require re-plating, to achieve its previous white look. There are many, many mixtures of white gold alloys available that have varying levels of yellow tint, and with different physical/mechanical properties. In fact, in order to establish a measurable standard for the degree of yellow color in white gold, The World Gold Council formed a White Gold Task Force to develop guidelines, or quantified “levels” of yellow tint that describe the degree of “whiteness” that a white gold alloy has. There are new alloy mixtures being developed all the time, with increasing levels of whiteness. And although none can achieve the absolute pure white of platinum, some have reached a whiteness level that does not require plating with platinum group metals to achieve a nice level of whiteness.
One result of a high nickel content as an alloying agent, is that the resultant alloy is a harder material than its equal in yellow gold and is more difficult to work with, both in casting and fabrication. It is also not uncommon for some people to have a reaction to white gold. This is actually a reaction to the nickel in the white gold alloy. A precaution associated with white gold, that is not true for yellow gold, is that chlorine will attack the nickel in the white gold alloy. Anyone with a gemstone mounted in white gold…especially a diamond in an engagement ring…should ensure that the ring is rinsed in pure water after swimming in a chlorinated pool, (or using chlorine bleach while cleaning), to remove any chlorine residue, which might attack the alloy. Repeated exposure over time, to chlorine in this way can result in a weakening of the metal prongs that secure the stone in the ring, (stress corrosion cracking), and may ultimately result in the loss of that stone. All jewelry should periodically be checked for integrity and wear, but white gold jewelry, (especially engagement rings), should be checked more frequently by a jeweler to ensure the integrity of the prongs that hold the stones in the ring.
Gold plate, gold-filled, rolled-gold plate, gold electroplate, and gold overlay are all terms used to describe essentially the same type of material…a thin layer of gold applied, through various means, over a base metal which is less costly. While the application process of the karat gold layer over the base metal is different in each case, the thickness requirements are also different. Because these differences are somewhat complicated and difficult, (not to mention BORING), they will not be covered here. The most important thing to know here is that gold plated items cannot be represented as “gold”, “fine gold”, or “karat gold”. There are even restrictions on the use of the plating terms listed above based on the purity of the gold used and the thickness of the layer of that gold.
As mentioned above, the platinum group consists of six elements: Platinum, Palladium, Iridium, Osmium, Rhodium, and Ruthenium. While these elements are quite rare, and are generally found together in nature, Platinum and Palladium are the most abundant. All the platinum group metals are not routinely used in jewelry. The most commonly used platinum group metals are; Platinum, Rhodium, and increasingly, Palladium. Platinum jewelry items are typically 90-95% pure Platinum. It is often alloyed with Iridium, Ruthenium, or Cobalt for use in jewelry. Compared to gold, which must be alloyed from 25% up to almost 50% with other metals to achieve the optimum physical and mechanical properties for use in jewelry, the platinum used in jewelry is a much purer metal. As shown in the matrix above, 14kt gold is 41.6% non-gold material, compared to the 90-95% purity of platinum. And because of its excellent durability and wear characteristics, Platinum jewelry will typically far outlast any other precious metal used in jewelry. When longevity and strength are concerns, Platinum is by far the best choice. And since its natural color is a silvery-white color, it does not need to be plated to make it appear white as in white gold alloys. Thus it will maintain its original color for life without any type of maintenance. Palladium is increasingly being used as a main ingredient in casting jewelry. It has many positive characteristics that bench jewelers can appreciate, and is not as expensive as its platinum cousin.
Silver is the last of the noble metals. It is the most plentiful, least valuable, not as durable as gold or platinum, and harder to work with in sizing and other operations that require a torch. And while silver is quite beautiful, it does tarnish very easily. Since ancient times silver has been valued and used as a medium of exchange. In fact, the British unit of currency, the pound sterling, (£), is based on silver. There are several different terms one might see used to describe the type of silver…or the purity of the alloy. The following are some of the terms used:
- Sterling silver — at least 92.5% pure silver. The alloying metal is usually copper. Anything of lower purity cannot be called “silver” or “solid silver”.
- Coin silver — derives from the FTC guidelines for S. coins when they were made of silver. Contains 90% pure silver and 10% copper. It cannot be called “silver” or “sterling”.
- Mexican silver — is usually 95% pure silver, and 5% copper. It is obviously a higher purity of silver than sterling, but not all silver that originates in Mexico is of this purity.
- Britannia silver — an alloy which is at least 95.84% pure silver.
Other terms found for silver include silver filled, (or silver overlay), which is a plating process using a fineness of at least 92.5%. The plating must make up at least 1/20 of the metal in the article. Silverplate is a layer of fine silver electronically deposited over a base metal. This cannot be called “silver” or sterling. Vermeil, (vur-MAY), is unique in that it has a gold overlay or plating on it.
There are some other remarkable metals that can also be included here, just because they are the new materials being used in the manufacture of jewelry today. Titanium is one such metal. Titanium is a silvery-white metal that is known more for its use in the manufacture of exotic aircraft and aerospace products. It is very light, and quite strong and wears similarly to gold. Another of these exotic metals is Tungsten. Tungsten is alloyed with carbon to form tungsten-carbide, which is the hardest metal currently possible. Next, the tungsten-carbide is alloyed with a small amount of nickel for use in the jewelry industry. This amazing tungsten-carbide metal is dark gray in color, and polishes to a high mirror finish that will last the lifetime of the ring under normal conditions. So the shiny, mirror finish that is on the ring when brand new, will still be there…scratch-free…for years and years to come. An even more recent and exotic material finding its way into jewelry manufacture, is zirconium. While this material has been used in the nuclear and medical industries for years, it is new in its application to jewelry. It is similar in appearance to titanium, but is more like tungsten-carbide in durability, and hardness.
You should consult with your jewelry professional to find out which of these many choices best suits your preferences and lifestyle.
– Platinum was brought to Europe by Spanish conquistadors in the Western Hemisphere who got it from the natives in Colombia. The Spaniards called it “platina”, or “little silver” in the sense of “unripe silver”. It was actually thought that this metal had not ripened, and would be thrown back in the rivers and caves so it could “mature”.
– Platinum will not oxidize…an ounce will remain an ounce forever.
– Platinum weights are used by the National Bureau of Standards for their standards.
– One fourth of the world’s annual platinum production is used by the Japanese and U.S. auto makers in catalytic converters. This is about one-half of the U.S. platinum use.
– One ounce of pure gold can be drawn out into a wire thread more than 50 miles long.
– One ounce of pure gold can be pounded or rolled into a 100 square foot sheet 1/250,000 of an inch thick.
– One ounce of pure gold could be used to plate a 747 with a layer of gold, one micron thick.
– All the gold ever found in the world totals around 100,000 tons.
– Gold nuggets found in nature tend to be only 70-80% pure.
– Largest gold nugget found in California is 35 lb.
– Largest gold nugget ever found…the Holtermann nugget found in Australia in 1887… weighed in at 472.5 lb.
Now go and impress your friends!