Strap classification.

Precious metal material
(1) platinum is a rare and expensive natural pure white metal, is one of the world's rarest jewelry with precious metals, from year to year supplies only 5% of the gold, has almost twice as much on the strength of the gold, 30 times more rare than the gold. Platinum, pure and pure, with a purity of up to 90%, is natural, and will not fade. Pt900 represents platinum jewelry with a purity of 90%, and Pt950 indicates a purity of 95% platinum jewelry.
K Gold is an alloy that is mixed with other metals, because it is Karat Gold, so it is called K Gold. Precious metal parts, 24 k gold, but gold is not suitable for making the watch is too soft, must mix the other metals to strengthen hardness, general is given priority to with silver, copper and palladium, but no matter which kind of metal mixture, the proportion of gold were accounted for 75%. As the proportion of gold, silver and copper, can produce five different colour and lustre of material, represented respectively by N copper content of high and low, such as copper content in the highest red gold in 5 N, said the correct statement is white K gold and platinum.
3 and a half) gold
The combination of stainless steel and 18K gold is used to present a unique double color aesthetic.
4) baojin's case is stainless steel, and it is outsourced to a gold alloy, which is made into a whole by mechanical rolling. Its thickness is measured in microns, and 1 micron is 1/1000mm. The maximum thickness is 10 to 15 microns, usually only 2 to 3 microns.
5) plating (gold plated, thanks brother wiiasa, plating should be put in precious metals attribute, the court explained below) plating is common in modern watches watchcase adornment method, rise of electroplating technology in the seventy s, due to the plating uniform and firm, than the cost is low and not easy to fall off, plated with gold and have no forging yellow shell color, the possibility of corrosion, so will soon be out of the market.
6) silver "in terms of purity, 925 is not the highest purity of silver! You can see the domestic instant silver respectively 99.99%, 99.95%, 99.90%, three kinds of purity, these three are too soft, not suitable for jewelry, with 92.5% of the commonly do jewelry is the most suitable (hardness, ductility, etc.), so also can call 925 sterling silver. But it's not really pure silver." Silver precious metals is an ancient, is the 18th century and used to watch the most used materials, represents the purity of silver, 925 is the highest purity of silver (not the highest purity, common is 925 - suitable for jewelry, 975 - for tableware, 990, and more pure - trial). Silver is an active metal that reacts chemically with the sulfur in the air, producing a black oxide layer that darkens the silver. It is far worse than gold in table applications, because it is so easily tarnished by water, moisture and other causes.