percentage - gold750 (18K)
necklace / pure gold, pure silver, pure copper, 18K gold (chain)
75% gold (Au) and 25% mixture of silver (Ag) and copper (Cu). This is a standard alloy for gold, and it's known as 18K gold or gold750. I combined 75% of fine gold bar and 25% of copper : silver (5 : 5) bar. If it's melted, it makes an alloy of 18K gold = gold750.