Certain qualities make noble metals gold, platinum, and silver marvelous jewelry materials. However, remarkable differences between the three metals exist. If you are planning to buy a proposal ring (求婚戒指) then you must read the article to get a better idea about the ring you should buy.
Gold, platinum, and silver, sometimes referred to as the “precious” or “noble” metals, are the raw materials most frequently used for jewelry. Although each metal has its own unique qualities, the three metals share certain characteristics which make them most ideal for jewelry.
Briefly, the Gemological Institute of America (GIA) contends that to be successful in jewelry making, a metal must possess each of these four qualities: allure, workability, durability, and rarity. In both practical and aesthetic terms, without each of the four qualities, metal is not best-suited for jewelry, according to the GIA’s Jewelry Essentials guide (GIA publication, 2007).
Precious Metals are Appealing, Workable, Durable, and Scarce
Allure is a combination of three things. First, an object’s color; second, an object’s surface appearance in reflected light, called luster; and, third, an object’s weight compared to size, which is heft.
Workability refers to an object’s malleability, ie, its ability to be stretched in all directions without breaking. Also, workability involves a material’s ductility, specifically, its ability to be formed into shapes and its ability to hold those forms.
Durability is concerned with a material’s strength and resistance to corrosion. A jewelry metal must be able to hold gemstones without wearing away and to withstand the test of time.
Rarity is about the actual amount of raw material present on the earth’s crust, combined with the time and effort necessary to mine or release each material from its natural environment. All four characteristics must be present in a material to make it “precious,” hence suitable, for lasting jewelry objects.
Precious Metals Mix with Other Metals for Ultimate Jewelry Alloys
It is well-known that certain mixtures of raw metals make superior jewelry materials over single-source metal jewelry. Mixtures of two or more metals are called alloys. Alloys are used to make metals more workable, more durable; to change or improve the appearance, and to reduce manufacturing costs. Also, a case can be made that using alloys may help preserve certain precious natural resources.
GIA sources say that even a small variation in metal content affects the value and physical properties of precious metals. What this means is that 14 karats (14K) gold and 24 karats (24K) gold are not at all the same in their material make-up, visual appearance, or durability. Also, manufacturers often use different combinations of alloys and different percentages or ratios of alloys. So, in effect, all 14K gold, for example, is not the same in material content. this may be important for jewelry wearers with metal sensitivities.
It is important to understand differences in metal alloys when considering jewelry metals because very rarely will you find pure gold, pure platinum or pure silver in jewelry. Note: A karat (abbreviated as “K” or “Kt”) is a unit of measure for the purity of gold equal to 1/24 part.
Specific precious metal content, known as “fineness,” is stated in parts-per-thousand, based upon weight. For example, gold with a fineness of 750 has 750 parts (75%) gold and 250 parts (25%) other metals. Platinum with a fineness of 950 is 95% percent platinum and 5% ruthenium or other platinum metal. By definition, sterling silver is 92.5% silver and 7.5% copper. In the United States, the fineness of silver must be at least 92.75% or the material may not be labeled “silver.”
Gold is Easiest to Fashion into Jewelry
In addition to its distinctive warm color, gold is highly workable and is known as the precious metal most easily fashioned into jewelry. However, the same characteristics that make pure gold highly workable also make pure gold highly susceptible to surface blemishes like scratches. Most of the wedding rings (結婚戒指) are made up of gold.
By adding different types of base metals in different amounts to gold, the alloys created can improve gold’s durability and change other characteristics. For example, different base metals create gold alloys of different shades and colors. Adding copper makes the gold reddish, adding silver makes the alloy more greenish, and adding Nickle or palladium whitens gold. Contemporary jewelry designers are mixing new combinations of base metals to produce jewelry pieces in “black” gold, “brown” gold, and “blue” gold, according to Antoinette Matlins and A.C. Bonanno in their book Jewelry & Gems The Buying Guide (Gemstone Press, 2006).
Some base metals are heavier than others, making an alloy with one base metal harder than an alloy using another base metal. In the US, 14K gold, or 14 parts gold, 10 Parts other metals by weight, is 58.3 percent precious metal of 583 parts per thousand. This alloy is quite common and harder than pure 24K gold. By the same token, 18K gold is 18 parts gold, 6 parts other metals by weight, 75 percent precious metal or 750 parts per thousand. 18K gold is softer than 14K but still harder than 24K gold. Generally, alloys with the most gold content are the most expensive.
White Gold Needs Care
Because gold is not naturally “white,” white gold is created by making a gold alloy with whitening metals. Then, since the white gold is not totally white, writes gemologist Reneé Newman in her book, Diamond Buying Guide (International Jewelry Publications, 2008), “it needs to be plated with a metal called rhodium to achieve the high white luster of platinum.” Over time, this plating wears off and needs to be replated in order to maintain the “whiteness” of the alloy. Furthermore, while gold made with Nickle is vulnerable to stress cracking and stress corrosion.
White gold is more resistant to wear and abrasions than yellow gold, however, it is not as resistant as platinum because gold is not as dense as platinum. All gold is sensitive to chlorine and should not be worn in swimming pools or hot tubs.
Platinum is Strong and Durable
Prior to World War II, platinum, a relative newcomer in the world of known metals, was the preferred “white” metal for jewelry. When the United States declared platinum a strategic metal and made it impossible for use in jewelry, white gold was substituted for platinum in jewelry fashioning, according to the GIA.
Pure platinum is harder than pure gold. And, overall, platinum is an extremely strong and durable material. This makes it an excellent choice for long-lasting jewelry pieces and for important gemstone settings. Often, it is used for intricate jewelry pieces due to its durability. Platinum resists abrasion better than gold because platinum molecules move around and can be reworked. By contrast, gold tends to wear away over time. Also, platinum ages with a distinct, soft patina, however, the patina can be polished periodically for a brighter finish and luster.
Generally, platinum is not considered to be affected by chlorine. However, if there is gold in the solder joints of a platinum piece, the jewelry will be at risk, just as a gold piece would be at risk in chlorine.
Platinum’s very high melting point makes it a challenging material for jewelers to fashion into jewelry. So, for jewelry making, platinum is usually alloyed with other metals from the platinum group, including ruthenium and iridium. Mixing the platinum metals creates alloys that are even harder than platinum itself. Yet, interestingly, even though pure platinum is harder than pure gold, both pure platinum, and alloyed platinum are not as hard as alloyed gold.
Silver is the Most Lustrous of Precious Metals
Silver is the most lustrous, or reflective, of the precious metals. Also, silver is the whitest metal. However, silver is considered to be too soft by itself for fashioning jewelry. The most popular silver alloy worldwide, sterling silver, contains at least 92.5 percent pure silver, with copper as the other metal in the alloy. Copper improves the strength and durability of silver. Also, a silver alloy tarnishes less than pure silver. Yet, any silver will fade over time.
Silver is wonderfully malleable and it is easily hammered and formed into jewelry shapes. Silver melts at a lower temperature than gold.
Beware of silver imposters. For example, “Nickle silver” actually contains no silver at all. It is an alloy composed of the base metals copper, zinc, and nickel that is made to resemble real silver.