Silver 925, also known as Sterling Silver, contains 92.5% silver and 7.5% copper. Pure silver is not used in jewelry making, as it is too soft. Silver has a seductive look with its warm color-temperature and has been used in jewelry making since ancient times. The disadvantage of silver is: It can react to sulfur in the air (depending on air quality and skin type). This is commonly known as ´tarnishing´ or ´oxidation´. The best way to remove these dark spots is the following: polishing cloth boil water in a pan and add some salt and a piece of uncoated aluminium foil. Then put your piece of jewel into the pan and "pickle" it wait for a while. Effective are also polish products especially made for silver-cleaning.
Zirconia (molecular formula: ZrO2, Zirconium dioxide) is synthetic substitute for diamond . Its hardness is almost as high as the one of diamond (8.5 as opposed to 10) which makes it resistable. However, it may scratch other material easily. Zirconia can be produced in different colours and levels of transparency. It is normally cut in faces (in the same way as glass).