A grinding wheel consists of the abrasive that does the cutting, and the bond that holds the abrasive particles together. There are two types of abrasives.
1. Natural abrasive The natural abrasives are emery and corrundum,These are impure forms of aluminium oxide.
2. Artificial abrasive Artificial abrasives are silicon carbide and aluminium oxide.

When the cutting edge of a grinding wheel takes a glass-like appearance due to wear of abrasive grains then it is called glazing of the grinding wheel. Glazing decreases the rate of grinding. The glazing in the grinding wheels takes place when the wheel is too hard or it revolves at a very high speed.
Thus the glazing may be decreased by using a softer wheel or decreasing the wheel speed.
The process of changing the shape of grinding wheel as it becomes worn due to breaking away of the abrasive and bond is called truing.
The process of improving the cutting action of the grinding wheel is called dressing.