High quality limestone for the manufacture of container and flat glass
Limestone produced by Longcliffe brings massive economic and environmental benefits to the whole of the UK. Major uses of our limestone include in the glass and ceramics industries include:
Most of the glass we see around us in our everyday lives in the form of bottles and jars, flat glass for windows or for drinking glasses is known as commercial glass or soda-lime glass, as soda ash is used in its manufacture.
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. All bottles and jars are now made automatically by one of two methods - 'Press and Blow' or 'Blow and Blow' using compressed air. 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 <0.036% iron oxide (Fe203). Iron is a serious impurity that can adversely affect the colour of the glass. The Longcliffe limestone supplied to the glass industry is of an extremely high purity and contains very low levels of metal contaminants.
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 two manufacturing processes for producing flat glass in the UK are the float glass and rolled glass processes.
The main flat glass products are for high quality glazing in homes, offices, hotels, shops, vehicles, public buildings and glass for horticulture; wired glasses for fire resistance; patterned glass for privacy and decoration; and a wide range of glass for environmental control and energy conservation.
Calcium carbonate has traditionally been a source of CaO in raw glazes. In low-fire bodies, calcium carbonate is sometimes added in small amounts as a filler to reduce fired shrinkage. It is also common to see calcium carbonate included in porous earthenware body recipes to prevent moisture expansion (causes glazes to craze).