Different types of glass

Glass should not be thought of as just a functional material to let light into an area; it can also be used to add decorative effect. But it is important to choose the right kind of glass for the right place so the final job is effective, attractive and safe. The wrong type of glass used in the wrong position can be unsatisfactory and present a serious hazard to personnel safety.

Types of glass

There are a number of different types of glass, in a range of patterns and tints, and it is important to decide which is most suited for a particular job.

'Ordinary' sheet glass

This glass is made by passing the molten glass through rollers; this process gives an almost flat finish but the effects of the rollers upon the molten glass makes some distortion inevitable. The glass can be used in domestic windows etc. but the relatively low cost of float glass (with its lack of distortion) has tended to restrict ordinary sheet glass to glazing greenhouses and garden sheds where the visual distortions do not matter.

Sheet glass can be cut a glass cutter and no special equipment is necessary. The glass is often available in standard sizes to suit 'standard' glasshouses, these sizes tend to be comparatively cheaper than glass cut to size.

Float glass (plate)

Float glass gets its name from the method of production used to manufacture it. The molten glass is 'floated' onto a bed of molten tin - this produces a glass which is flat and distortion free.

Float glass can be cut using a glass cutter and no special equipment is necessary. Float glass is suitable for fixed and opening windows above waist height.

Energy efficient glass

Some manufacturers produce float glass with a special thin coating on one side which, allows the suns energy to pass through in one direction while reducing the thermal transfer the other way. The principle behind this is the difference in thermal wavelength of energy transmitted from the sun and that transmitted from the heat within a room.

The special coating often gives a very slight brown or grey tint to the glass. The coating is not very robust and would not last very long if subjected to normal cleaning or external weather conditions - for these reasons, this type of glass is normally only used in sealed double (or triple) glazed units with the special coating on the inside.

Self cleaning glass

Some manufacturers produce float glass with a special thin 'photocatalytic' coating on one side. This coating uses the ultraviolet rays from the sun to steadily break down any organic dirt on the surface using the photocatalytic effect and thus loosen the dirt from the glass.

Self–cleaning glass also has 'hydrophilic' properties which means that when rain runs down the pane of glass, it will wash away the dirt previously loosened. Together, the 'photocatalytic' and 'hydrophilic' effects allow the glass to stay cleaner for a longer period than untreated glass.

Small particles of dirt will loosen and (providing there is rain) be washed off fairly quickly, however, bird droppings and other large bits of dirt, will take longer to be cleaned off.

Self cleaning glass may, from time to time, need additional cleaning and great care needs to be taken with such cleaning to avoid damaging the surface coating - never use any abrasive cleaner, check with the particular manufacturer for detailed guidelines. If additional cleaning is carried out, the self-cleaning properties may take a period of time to become active again.

Patterned (obscured glass)

Made from flat glass, this type has a design rolled onto one side during manufacture. It can be used for decorative effect and/or to provide privacy. Patterned glass is available in a range of coloured tints as well as plain.

A variety of pattern designs are available, each pattern normally has an quoted distortion number, from 1 to 5, 1 being very little distortion, 5 being a high level of diffusion.

On external glazing, the patterned side is usually on the inside so that atmospheric dirt can easily be removed from the relatively flat external face.

Toughened (Safety glass)

Toughened glass is produced by applying a special treatment to ordinary float glass after it has been cut to size and finished. The treatment involves heating the glass so that it begins to soften (about 620 degrees C) and then rapidly cooling it. This produces a glass which, if broken, breaks into small pieces without sharp edges. The treatment does increase the surface tension of the glass which can cause it to 'explode' if broken; this is more a dramatic effect than hazardous.

It is important to note that the treatment must be applied only after all cutting and processing has been completed, as once 'toughened', any attempt to cut the glass will cause it to shatter.

Toughened glass is ideal for glazed doors, low level windows (for safety) and for tabletops (where it can withstand high temperature associated with cooking pots etc.

Laminated glass

As the name suggests, laminated glass is made up of a sandwich of two or more sheets of glass (or plastic), bonded together by a flexible, normally transparent material.

If the glass is cracked or broken, the flexible material is designed to hold the glass fragments in place.

The glass used can be any of the other basic types (float, toughened, wired etc.) and they retain their original breaking properties.

Some laminated glass is laminated for other reasons than just keeping any broken glass in place, some provide decorative internal finishes to the glass while others act as fire breaks.

Wired glass

Wired glass incorporates a wire mesh (usually about 10mm spacing) in the middle of the glass. Should be glass crack or break, the wire tends to hold the glass together. It is ideal for roofing in such areas as a garage or conservatory where its 'industrial' look is not too unattractive.

Wired glass is generally not considered a Safety glass as the glass still breaks with sharp edges.

Wired glass is available as clear or obscured.

Mirrors

Mirrors are usually made from float glass 4-6mm thick, and silvered on one side. Mirrors are available for use without a surrounding frame, these usually are made from a type of safety glass. Old mirrors, and modern mirrors supplied within a frame, should not be used unframed as any damage to them might cause the glass to shatter dangerously.

Picture frame glass

Glass (and plastics) are available specifically for picture framing, these tend to be referred to as 'diffused reflection' glass or plastic. They have high transparency but low reflective properties to reduce reflections when the picture or photograph is viewed.

Most of these materials can easily be cut by the average diy person providing suitable tools and safety precautions are taken.