Soda-lime glass

Soda-lime glass, also called soda–lime–silica glass, is the most common type of glass, accounting for about 90% of manufactured glass products. It is widely used for windows, bottles, jars, and many other everyday items.

It is made primarily from three main ingredients:

• Silica (SiO) is the primary component, making up about 70-75% of the glass. It provides the structure and transparency.
• Soda (Sodium Oxide, NaO) derived from sodium carbonate (soda ash) lowers the melting point of the silica, making it easier to form the glass.
• Lime (Calcium Oxide, CaO) derived from limestone, is added to improve the chemical durability of the glass and prevent it from dissolving in water.

Other minor ingredients, such as alumina (AlO), magnesium oxide (MgO), and sometimes small amounts of other oxides, are added to enhance specific properties like durability, color, and resistance to weathering.

Soda-lime glass is clear and colourless in its pure form but can be tinted with the addition of metal oxides. It is relatively easy to melt and shape, making it ideal for mass production. The raw materials are abundant and inexpensive, making soda-lime glass affordable.

However, soda-lime glass is not very resistant to thermal shock or sudden changes in temperature, which can cause it to crack or shatter. It also has a relatively low resistance to chemicals and scratches compared to other types of glass, such as borosilicate glass.

NB Archaeological Evidence for Glassworking, Guidelines for Recovering, Analysing and Interpreting Evidence, published by Historic England in 2018, suggests that soda-lime glass: ‘Includes soda-ash and natron glass. Soda-lime glass is typical of the Iron Age, Roman and much of the early medieval periods, and also from around the 19th century.’

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