1. K gold case watch. "K" is the first letter of the German "Karat", a unit used to indicate the purity of gold. The larger the K number, the higher the gold content. Pure gold is 24K, and there are 5 kinds of common K gold case watches including 9K, 10K, 12K, 14K and 18K. The gold-containing signs of imported K gold case watches are generally brushed on the inside of the back cover of the watch; there are also women's heads (representing 18K), birds (representing 14K), and trees (representing 10K) as signs.
2. Gold-plated watch. It is chemically plated with a layer of gold alloy on the surface of the copper casing, and its thickness is measured in microns (symbol μ) as an even unit. 1 micron is equal to 1/1000 mm. The International Organization for Standardization stipulates that the marking of gold-plated watches is: the English letter "C" represents the K number; "P" represents the thickness. For example, "C18P20" is a gold-plated watch with a purity of 18K and a thickness of 20μ.
3. Gold watch. Its case is made of copper, covered with a layer of gold alloy, which is mechanically rolled into a whole. In addition, there is a steel backpack gold watch, the back cover of this type of watch is stainless steel, and only the case is gold-plated. Gold-clad watches are only marked with thickness, not purity. The International Organization for Standardization stipulates that the marking of gold is to use the English letter "L" to indicate the thickness. For example, "L40" means that the thickness of gold foil is 40μ, and there are generally 4 kinds of thicknesses such as 20μ, 40μ, 60μ, 80μ.
4. Gold ring watch. Generally, it is an all-steel watch, and only a circle of K gold skin is set on the outer side of the upper case along the watch glass, which can be separated from the case. The purity of K gold is 7K, 9K, 10K, 14K, etc., and the thickness is generally less than 0.5 mm.
5. Gold hoop ear case. It is a K-gold piece made separately, and the cover is permanently bonded to the upper end of the 4 feet of the watch, and the others are the same as the gold ring watch. The International Organization for Standardization stipulates that the labeling of gold stickers is: the letter "C" indicates the thickness, and generally does not indicate the purity. For example, "C250" means that the thickness of the gold paste is 250 microns. At present, there are three kinds of gold paste thickness: 200 microns, 250 microns, and 300 microns. There is also a yellow-plated watch on the current market. It is a general term for a golden-yellow watch case that generally does not contain gold components. It is plated with titanium.