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.

The main constituent of practically all commercial glass is sand. Sand by itself can be fused to produce glass but the temperature at which this can be achieved is about 1700oC. Adding other chemicals to sand can considerably reduce the temperature of fusion.

Commonly known as lead crystal, lead glass is used to make a wide variety of decorative glass objects.

It is made by using lead oxide instead of calcium oxide, and potassium oxide instead of all or most of the sodium oxide. The traditional English full lead crystal contains at least 30% lead oxide (PbO) but any glass containing at least 24% PbO can be described as lead crystal. Glass containing less than 24% PbO, is known simply as crystal glass. The lead is locked into the crystal structure of the glass so there is no risk to human health.

Most of us are more familiar with this type of glass in the form of ovenware and other heat-resisting ware, better known under the trade name Pyrex.

Borosilicate glass, the third major group, is made mainly of silica (70-80%) and boric oxide (7-13%) with smaller amounts of the alkalis (sodium and potassium oxides) and aluminium oxide. This type of glass has a relatively low alkali content and consequently has good chemical durability and thermal shock resistance (it doesn't break when changing temperature quickly). As a result it is widely used in the chemical industry, for laboratory apparatus, for ampoules and other pharmaceutical containers, for various high intensity lighting applications and as glass fibres for textile and plastic reinforcement.

Glass fibre has many uses from roof insulation to medical equipment and its composition varies depending on its application.

For building insulation and glass wool the type of glass used is normally soda lime. For textiles, an alumino-borosilicate glass with very low sodium oxide content is preferred because of its good chemical durability and high softening point. This is also the type of glass fibre used in the reinforced plastics to make protective helmets, boats, piping, car chassis, ropes, car exhausts and many other items.

Silica glass or vitreous silica is of considerable technical importance as it has a very low thermal expansion. This difficult to make glass contains tiny holes created using acids and is used for filtration. Porous glasses of this kind are commonly known as Vycor.

A small, but important type of glass, aluminosilicate, contains 20% aluminium oxide (alumina-Al2O3) often including calcium oxide, magnesium oxide and boric oxide in relatively small amounts, but with only very small amounts of soda or potash. It is able to withstand high temperatures and thermal shock and is typically used in combustion tubes, gauge glasses for high-pressure steam boilers, and in halogen-tungsten lamps capable of operating at temperature as high as 750oC.

Without this type of glass watching TV would be very dangerous. A television produces X-rays that need to be absorbed, otherwise they could in the long run cause health problems. The X-rays are absorbed by glass with minimum amounts of heavy oxides (lead, barium or strontium). Lead glass is commonly used for the funnel and neck of the TV tube, while glass containing barium is usually used for the screen.

Without borate glass the computer revolution would not have been possible as it's vitally important in producing electrical components. This type of glass, contains little or no silica and is used for soldering glass, metals or ceramics as it melts at the relatively low temperature of 450-550oC, well below that of normal glass, ceramics and many metals.

Some of these "Glass ceramics", formed typically from lithium aluminosilicate glass, are extremely resistant to thermal stock and have found several applications where this property is important, including cooker hobs, cooking ware, windows for gas or coal fires, mirror substrates for astronomical telescopes and missile nose cones.

An essential feature of glass is that it does not contain crystals. However, by deliberately stimulating crystal growth in glass it is possible to produce a type of glass with a controlled amount of crystallisation that can combine many of the best features of ceramics and glass.

Optical glasses will be found in scientific instruments, microscopes, fighter aircraft and most commonly in spectacles.

The most important properties are the refractive index and the dispersion. The index is a measure of how much the glass bends light. The dispersion is a measure of the way the glass splits white light into the colours of the rainbow. Glass makers use the variations in these characteristics to develop optical glasses.

Another application for which a large variety of glass compositions is used is sealing to metals for electrical and electronic components. Here the available glasses may be grouped according to their thermal expansion which must be matched with the thermal expansions of the respective metals so that sealing is possible without excessive strain being induced by the expansion differences.