Major uses of our high purity limestone include the production of container glass, flat glass and ceramics
Most commercial glasses consist essentially of silica together with soda (Na2O) and lime (CaO), the lime being partly replaced by magnesia (MgO) depending on the application. Lime is introduced into the glass melt as limestone (CaCO3) and magnesia by adding dolomite [CaMg(CO3)2].
Container glass is made from a specific mixture of sand, soda ash, limestone and other additives. Container glass is the material of which bottles and jars are made.
Limestone for glass-making must be of a very high purity and contain <0.035% iron oxide (Fe203). Iron is a serious impurity that can adversely affect the colour of the glass. The limestone supplied to the glass industry by Longcliffe is of an extremely high purity and contains very low levels of metal contaminants.
Most flat glass is similar in composition to container glass except that it contains a higher proportion of magnesium oxide. Consequently most lime is introduced using dolomite and only a little limestone is used to balance the CaO/MgO ratio.
The majority of flat glass is used in the production of high quality glazing for homes, commercial and public buildings, vehicles, and horticultural applications.
Calcium carbonate has traditionally been a source of CaO in raw glazes. It is also sometimes used in low-fire bodies to reduce fired shrinkage. It is also common to see calcium carbonate included in porous earthenware body recipes to prevent moisture expansion which otherwise causes glazes to craze.