The silica (sand) at the base of glass formation must be heated over 3,092°F (1,700°C) to melt. Fluxes (soda, potash, or lime), water, and recycled glass debris (cullet) are then added in order to facilitate its transformation. Different additives are also inserted depending on the subsequent use of the finished product such as magnesium oxide to make the glass more resistant or iron oxide to give it a greenish tint. The sandy mixture is then heated at about 2,732°F (1,500°C) in a furnace to turn into liquid glass.