Before discussing the cause of colour in more depth, it’s worth discussing the chemical composition of glass itself. There are actually different types of glass for different purposes. The vast majority of the glass we use on a daily basis is soda-lime glass; this is primarily a mixture of silicon dioxide, calcium oxide (lime) and sodium oxide (soda). It’s used for a range of purposes, including bottles, containers, window panes and drinking glasses. It’s not, however, the only type of glass we can make.