Metal Fineness and
Stamps
Scott Rowe, G.G.
14 Karat yellow gold is the most popular jewelry metal used in the United States. However, many jewelry items are produced using 10 Karat. 18 Karat gold is also rebounding in popularity. Unfortunately, the quality stamps can be confusing and sometimes enough doubt is raised concerning gold content that a jewelry item is not purchased. Hopefully, this article will dismiss any misunderstanding about metal fineness and their stamps.
First, quality stamps are regulated by the NATIONAL GOLD AND SILVER MARKING ACT. On October 1, 1981, revised Section 295 of Volume 15 of the United States Code, the law governing requirements for gold and silver marking, which is commonly known as the National Gold and Silver marking Act, went into effect. Originally enacted in 1906, this law never required one to indicate quality. However, if quality was disclosed, it had to be accurate within 1/2 Karat (without solder), or 1 Karat (with solder, article assayed in its entirety) from the disclosed mark. Criminal sanctions could be imposed for violations.
1961 was the year the law was amended to require the name or registered trademark of the firm responsible for the quality stamp. This law was later amended in 1970, 1976 and finally in 1981. The latest revision has the strictest requirements and actual fineness shall not be less by more than 3/1000ths parts (without solder), and 7/1000ths parts (with solder taken into account).
Please note: While the law requires that gold and silver jewelry carrying a quality mark also carry the registered trademark of the person or organization responsible for the for the guarantee of quality, there is no United States law requiring that gold or silver be quality marked in the first place! If no quality mark appears, it is legal, however, if a quality mark appears without a registered trademark, it is illegal.
Before fineness is discussed in detail, precious metals are weighing using TROY WEIGHT. The following are conversions of weights:
24 grains = 1 pennyweight (dwt.)
20 dwt = 1 ounce Troy
12 ounces Troy = 1 pound Troy
1 gram = .032151 Troy oz.
1.555 grams = 1 dwt
31.104 grams = 1 ounce Troy
28.35 grams = 1 ounce Avoirdupois (Postal Scales)
Metal Fineness is simply the content of Gold, Silver or Platinum versus Alloy. Alloys are the base metals mixed with precious metals to change properties such as color and hardness. Pure Gold is 24 Karat and is also represented by the designation ".9999 fine" gold. Karat stamps are a fractional representation of the pure Gold content of the jewelry item over the number 24 which can be express as a number. For example, 14 Karat gold is the fraction 14/24. 14 divided by 24 = .58333 which is represented by the stamp 585 in many foreign countries. 10 Karat gold is the fraction 10/24 which equals .417, stamped 417 and 18 Karat is 18/24 = .75 and has the corresponding stamp 750. It is simply a mathematic equation changing percentage into fractions or vise versa. So if you are asked what Karat gold is a ring stamped 375, simply multiply 24 X .375 = 9 Karat.
Yellow gold remains the top choice in jewelry here in the U.S., however, white metals are also popular, which means white gold, silver, and increasingly, platinum. Gold also comes in colors besides yellow and white. Red, rose, pink, green, blue, purple and even gray are other colors of gold and some can be quite subtle. White gold is usually 10% to 20% nickle, plus zink, copper and maybe platinum or manganese. Sometimes silver is also used as a coloring agent but nickel is prefered to give the white color and to harden the gold.
Silver is also alloyed with copper to make it harder. Sterling silver is 92.5% fine silver and 7.5% alloy. As in gold stamps, sterling silver is usually stamped 925, however, sometimes it is stamped SS
Platinum refers to a specific metal and a group known as the platinum group. There are six metals in the platinum group and five - platinum, iridium, palladium, ruthenium and rhodium - are used in jewelry. Platinum jewelry is usually 10 % Iridium and 90 % platinum, stamped 10%IRID PLAT, or IRID PLAT or 100IRID900PLAT. Some platinum is now being alloyed with 5% ruthenium. The reason platinum is alloyed is to make the metal harder.
14KP means plumb or accurate
Chlorine will dissolve gold, see the chemical corrosion test.
Platinum is the most noble of metals meaning it is not attacked by chemicals.
Please note that this article on precious metal is not complete at the time
of printing.
