18KGP and 23KGP are the marks of the emulation jewelry. It consists of two parts. 18K or 23K means a kind of mark; K stands for the content degree of golden purity. The comparison expression about K degree and content of golden content is that wt%=k/24*100%. Every K contains 4.166% gold which leads to 18K contain 75% gold and 23K contain about 95% gold.
There is a kind of alloy which is called Plape. It is a mark for a product that consists mainly of phosphorus and copper. It is covered with a golden layer under the high temperature and pressure and the layer has two kinds including covered gold and gold-plating. The gold-plating has a width of 1mic and the covered gold has 3mic.
Generally GP is the mark of gold-covering or gold-plating
jewelry. The formal part 18K or 23K means the content of golden surface.18KGP or 23KGP jewelry is mostly white not yellow. This is the mix of pure gold and K gold. One of the characteristics of gold is soft which makes it easier for the setting of diamond and make it harder for the falling of diamond. So people add silver, copper and zinc to the gold in order to strengthen the hardness and flexibility of it. This kind of jewelry is called K gold. Several degrees of K gold are used to set the diamond on which shows the grace of gold, make up to it. You can have several colors in the prospect of function. There are several colors in the international market and the normal color is white and yellow. K gold can be divided into white K gold or yellow K gold. The most common color in the jewelry is Au-Ag-Cu(-Zn) and most of white K gold has a color of Au-Ag-Ni(Cu、Zn) and Au-Ag-Pd(-Zn~Cu). If you put 25% palladium, nickel and zinc into the gold then it will turn white. However, its main part is gold which make it called WHITEGOLD. Pay attention to that platinum and white gold has not the same concept and some sneaky manufacturers take in consumers for that. Some people even lie that white gold is just the folk name of platinum.
18KGP means the jewelry which is covered with a lay of 18K gold-covering or gold-plating. 23KGP means a lay of 23K gold-covering or gold-plating. 925 or the silver 925 is the mark of silver jewelry.This paper from the http://www.jewelryshopvip.com