Fused quartz is produced by fusing (melting) high-purity silica sand, which consists of quartz crystals. There are four basic types of commercial silica glass:
* Type I is produced by induction melting natural quartz in a vacuum or an inert atmosphere.
* Type II is produced by fusing quartz crystal powder in a high-temperature flame.
* Type III is produced by burning SiCl in a hydrogen-oxygen flame.
* Type IV is produced by burning SiCl in a water vapor-free plasma flame.
Quartz contains only silicon and oxygen, although commercial quartz glass often contains impurities. Two dominant impurities are aluminium and titanium which affect the optical transmission at ultraviolet wavelengths. If water is present in the manufacturing process, hydroxyl (OH) groups may become embedded which reduces transmission in the infrared.