Beyond just simple purity hallmarks (i.e. 10k, 14k, 18k, etc.) there are some other types of markings that jewelers also use when hallmarking τιμη χρυσου τωρα jewelry which include letters such as GF, EP, and KP. Below is an explanation of a few of the most common that you may come across which would have a direct effect on the market value of your items.
GF – stands for “Gold Filled”, also known as “Rolled Gold” or “Rolled Gold Plate” and is composed of a solid layer of Au (or a gold alloy) bonded with heat and pressure to a base metal such as brass. Most high quality gold filled pieces have the same appearance as 14 karat (58%) gold. In the U.S. the quality of gold filled is defined by the Federal Trade Commission. If the gold layer is 10k fineness the minimum layer of karat gold in an item stamped GF must equal at least 1/10 the total weight of the item. If the gold layer is 12k or higher the minimum layer of karat gold in an item stamped GF must equal at least 1/20 the total weight of the item. 1/20 12k GF and 1/20 14k GF are the most common stamps found on gold-filled jewelry, 1/10 10k is also fairly common.
“Double clad” gold filled sheet is produced with 1/2 the thickness of gold on each side. 1/20 14kt double clad gold-filled has a layer on each side of 1/40th 14k, making the total content of gold 1/20 of the total weight of the item. The thinner layer on each side does not wear as well as single clad gold-filled.
The Federal Trade Commission allows the use of “Rolled Gold Plate” or “R.G.P.” on items with a lower thickness of gold than are required for “gold-filled.” 1/60 12k RGP designates a 12k gold layer that is 1/60 of the total weight of the item. This lower quality does not wear as well as gold-filled items.
Gold-filled items, even with daily wear, can last 5 to 30 years but will eventually wear through. The gold layer on gold-plated jewelry varies greatly depending on the manufacturer, so there is no single, simple comparison. Gold-filled items are 50 to 100,000 times thicker than regular gold plating, and 17 to 25,000 times thicker than heavy gold electroplate (sometimes stamped HGE or HGP which is commonly found on items such as flashy cubic zirconia “cocktail rings”).
EP – stands for “electroplating” and is used to make items out of non-precious metals which are then coated in a very thin layer of pure gold by the process of electroplating. Federal standards require items that are stamped “EP” to have a thickness of at least 7 millionths of an inch of at least 10K gold. Gold electroplated items will have a much smaller amount of actual gold content as compared to “gold filled” items and therefore have a much lower value (in regards to pure gold content).
KP – stands for “karat plumb” that’s “plumb” as in “straight” or “exact”, so 14kp gold is exactly 58.555% gold. This marking relates to some odd, and now obsolete US laws. 14 karat means that an item is 14/24 gold with the remainder being other metals. The problem comes with the rounding. 13.88/24 would be rounded to 14k under the old US law and 13k under matching British law. Obviously, this could cause some confusion, especially for US manufacturers who want to sell in Europe. European customers simply didn’t believe the marks were accurate. They started using the mark 14kp to mean that it is at least 14.00/24 parts gold. The rules have actually changed to where US manufacturers are using the same rules as the rest of the world but the 14kp system of naming still lives on. For new pieces, 14k and 14kp both mean that it’s at least 14.00/24 parts gold. In older pieces 14k might contain as little as 13.51/24.