Soda–lime glass

[2][3] The manufacturing process for soda–lime glass consists in melting the raw materials, which are the silica, soda (Na2O), hydrated lime (Ca(OH)2), dolomite (CaMg(CO3)2, which provides the magnesium oxide), and aluminium oxide; along with small quantities of fining agents (e.g., sodium sulfate (Na2SO4), sodium chloride (NaCl), etc.)

[4] The soda and the lime serve as a flux lowering the melting temperature of silica (1580 °C) as well as causing the mixture to soften as it heats, starting at as low as 700 °C.

The two types differ in the application, production method (float process for windows, blowing and pressing for containers), and chemical composition.

[5] From the lower content of highly water-soluble ions (sodium and magnesium) in container glass comes its slightly higher chemical durability against water, which is required especially for storage of beverages and food.

Whereas pure silica has excellent resistance to thermal shock, being able to survive immersion in water while red hot, its high melting temperature (1723 °C) and viscosity make it difficult to work with.

The glass is readily formable into objects when it has a viscosity of 104 poises, typically reached at a temperature around 900 °C.

Though apparently hardened, soda–lime glass can nonetheless be annealed to remove internal stresses with about 15 minutes at 1014 poises, near 500 °C.

Reusable soda–lime glass milk bottles
Old window made from soda-lime flat glass, Jena , Germany: The distorted reflections of a tree indicate that the flat glass was possibly not made by the float glass process.