Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron oxide impurities produce a green tint which can be viewed in thick pieces or with the aid of scientific instruments. Further metals and metal oxides can be added to glass during its manufacture to change its color which can enhance its aesthetic appeal. Examples of these additives are listed below:
Iron(II) oxide may be added to glass resulting in bluish-green glass which is frequently used in beer bottles. Together with chromium it gives a richer green color, used for wine bottles.