1. Conventional Types
Based on composition and properties, the conventional glass may be classified as soda lime or crown glass, flint glass, and Pyrex or heat-resistant glass.
(i) Soda Lime or Crown Glass
The composition by weight, in general, is sand 75 parts, lime 12.5 parts, soda 12.5 parts, alumina 1 part and waste glass 50 parts. It can be easily fused at comparatively low temperatures. It is quite cheap and available in clean and clear state.
It is principally used for window glass, plate glass and container glass (such as bottles, tumblers, etc.).
(ii) Flint Glass
The composition of flint glass is sand 100 parts, lead 70 parts, potash 32 parts and waste glass 10 parts. It liquefies at a lower temperature compared to soda lime glass and has better lustre. As the lead compounds are reduced easily, the glass must be melted in oxidising atmosphere, etc.
It is used for tablewares and for optical works. It has also wide range of use as electric lamps, thermometers, electron tubes, laboratory apparatuses, container for foods, etc.
(iii) Pyrex or Heat-resistant Glass
Both the above two glasses when subjected to sudden temperatures are not able to sustain because of large coefficients of thermal expansion. Only the basic oxides make them susceptible to chemical attack by water and acids. Elimination of the basic oxides and inclusion of boron oxide produce a glass that is very resistant to thermal shock and to attack by water and acids. The composition of material for such a glass by weight are silica 80 parts, boron oxide 14 parts, sodium oxide 4 parts, alumina 2 parts, with traces of potassium oxide, calcium oxide and magnesium oxide. In order to melt such as mixture, a very high temperature is required.
These glasses are called borosilicate glasses which are extensively used for cooking utensils and laboratory wares.
2. Special Types of Glasses
Special types of glasses are sheet glass, plate glass, float glass, wired glass, translucent glass, glass blocks, safety glass, bullet-proof glass, tinted glass, structural glass, etc.
(i) Sheet Glass
This is mainly used for small panels of doors and windows. These glasses are to be free from blisters, scratches, waves, bubbles, etc. It is manufactured in thickness varying from 1.5–5 mm and sizes up to 1.5 m × 1 m.
(ii) Plate Glass
It is available in thickness varying from 3–32 mm. This type of glass is stronger and more transparent with very less waviness. It is generally used for large size panels such as waiting halls, shopping complexes, etc. There are three varieties of this type of glass, namely rough cast, rolled (or patterned) and polished glass. Generally the polished variety is denoted as plate glass.
(iii) Flutted Glass
These are the glasses which have corrugations on one side of the plate glass. The other side is wavy but smooth. In this type, the light is admitted without the glare of the sun. It is used in situations where privacy without obstruction of light is needed. Ribs may be in the horizontal or vertical directions. Horizontal ribs give more light in the middle and less at the sides. The upright ribs give more light at the sides and less in the middle. It is thus more ideal to use for skylight roofs and for windows of industries and railway stations.
(iv) Float Glass
This type of glass is prepared by passing the molten glass through a molten tin bath (float bath). Because of the free-standing surface of the tin bath is very smooth, the float glass is of uniform thickness. It possesses excellent optical clarity and aesthetic appearance. Finally it is annealed to relieve all the stress. This is mainly used for large-sized shop windows and facade of tall buildings.
(v) Wired Glass
In this type of glass, wire-netting material is embedded during the time of manufacture. It has high resisting power compared to ordinary plate glass. Because of wire-netting, it does not fall into pieces when broken. It is used for fire resisting doors and windows and for skylights and roofs.
(vi) Translucent Glass
This glass is also called as obscured glass or frosted glass. In such glasses, a pattern or texture is imprinted on one or both faces. This prevents the image being seen through. The textured side should face the inside of a place (to be made obscure) and the plane glass side should face the other side. This type of glasses are used for doors and windows of bedroom, bath room, lavatories, etc.
(vii) Bullet-proof Glass
This type of glass is prepared by following special techniques. Here, the glass is made of several layers of plate glass with alternate layers of vinyl resin plastics. Further the inner layers are thicker than outer layers. At the time of manufacturing, special care is taken for heating and cooling of layers. Thickness of this type of glasses vary from 15–75 mm. Special quality of the glass is that it will not allow bullet to pierce through it. It is used in special type of cars, bank counters, jewellery stores, etc.
(viii) Glass Blocks
These are glass units that consist of two halves fused together so as to form a hallow inside. These blocks provide insulator against heat, cold and noise. These blocks are used for constructing wall panels.
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