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Types of glass
There are many different types of glass. They differ in terms of their chemical composition, the method used to produce them or their processing behaviour. Generally, they are categorised according to their chemical composition. A differentiation is made between
soda-lime glass, lead glass and borosilicate glass. These three types of glass make up around 95 percent of the cullet glass used in the production process. The remaining 5 percent of glass is special-purpose glass.
Soda-lime glass is the glass produced in by far the largest quantities of all mass produced glass types. As the name indicates, the main constituents in addition to sand are soda and lime. A typical soda-lime glass contains 71 to 75 percent sand (SiO2), 12 to 16 percent sodium bicarbonate (Na2O), 10 to 15 percent lime (CaO) and small quantities of other substances such as dyes. Soda-lime glass is used to make bottles, food jars, simple drinking glasses and sheet glass products. Soda-lime glass is light permeable and has a smooth, fine-pored surface, making it easy to clean. It also expands very quickly under the influence of heat so care should always be taking when putting hot water into a soda-lime glass container.
Crystal glass looks beautiful when cut as a result of its high refraction index. It has a far higher density than soda-lime glass. In our everyday lives, we use crystal glass to make drinking glasses, vases, bowls, ashtrays and decorative ornaments. Its composition is 54 to 65 percent sand, 13 to 15 percent alkali oxide and several other oxides. Glass containing more than 18 percent lead oxide is also known as lead crystal glass. However, lead oxide is hardly used today in glass production. Crystal glass only accounts for less than 0.5 percent of total tableware glass production in Germany.
Special glass is used for special technical and scientific applications. Its composition can vary and it includes numerous chemical elements. Examples of special glass are lenses, glass products used by the electrical and electronics industries and glass ceramics.
How is curved glass made?
Manufacturing curved glass is a time-consuming, highly specialised job. You could almost say it's a ‘pane' to produce.
Workers cut the sheet of glass to size and then clean and polish it, using a UV lamp to check for dust or impurities (any rogue particles would cause the glass to crack or shatter). They construct a steel mould shaped to the curve radius and dimensions of the desired piece. To stop the pane sticking to the mould, the glass is painted with a mixture of detergent and calcium carbonate.
Then, it is placed on the mould and loaded into the kiln. The manufacturers crank up the heat to 700°C, hot enough to loosen the bonds between the silica molecules so that the glass starts to soften and bend to the profile of the mould. Once in shape, the glass is gradually cooled over a period of about two hours.