Allder Group - Glass and Locks

Allder Group - Glass & Locks

History of Glass

You will find in depth information on sites such as the fantastic Wikipedia, but for a basic easy read….

Originally glass was spun into glass "discs". The centre part where it was connected was consider waste and called "the Pig" This was the cheapest part available and virtually discarded. The poor would therefore have windows made up of these made into a larger pane by joining them with lead "H" section, now known as "came". Ironically Hand Spun Bullion as they are now known, are very expensive. Glass, due to the way it was made with the centre piece needing to be cut out, could only be made in small pieces. This will probably be the reason old houses in Tudor Times only had small windows.

A new method needed to be developed and rolled glass was born. As it sounds moulten glass was rolled out. This was better in some ways as bigger pieces could be produced but on the down side you had massive distortion and it was flawed from the surface it was rolled on.

The method of pulling it was then employed naming it "Drawn" glass. A better process but still lacking clarity as the varying thickness created a distorted image through it.

Then came Float glass…

Float glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and various low melting point alloys were used in the past. This method gives the sheet uniform thickness and very flat surfaces, optically perfect. Modern windows are made from float glass.

The float glass process is also known as the Pilkington process, named after the British glass manufacturer Pilkington, invented by Alistair Pilkington who interestingly was not related to the Pilkington family, just had the same name!



This became the bed rock of glass manufacturing worldwide and the process is still the one used today. Since then the manufacturing of laminated glass has developed. This is as it sounds, literally bonding two or more sheets of glass together to create either safety, security, bullet and blast resistant, or acoustic glazing. This is available in thicknesses ranging from 4.4mm right up to50mm +. Some ballistic laminated incorporates a polycarbonate layer as an internal core to reduce the weight of the product. Bear in mind glass weighs 2.6KG per 1mm of thickness over a square metre. Therefore the average shopfront glass of 3M x 3M say 10.8mm thick will weigh 252.72KG, over a quarter of a tonne. This helps explain why we quite often need lots of men when installing such panes. The biggest we have installed was 5500 x 3200 in 12.8mm which weighed 585KG, over half a tonne. This would have taken 24 men to install, based on the HSE safe lifting load of 25KG per man. For this reason we used a crane with a pneumatic suction lifter attached to the jib.

Toughened safety glass is when float glass is heated and cooled in quick succession many times. This changes the molecular structure of the glass giving it massive surface tension. This increases its strength 5 fold and if broken shatters into relatively harmless small pieces. Standard float glass, being a super liquid, not a solid, breaks into shards that can be very dangerous.

Wired glass is available in clear or obscured. The wires are layered into molten glass but this creates distortion. To make clear wired glass it starts off as cast (obscured/tetured) created by the process of introducing the wires. It is then ground down and polished, hence its so expensive. Both the clear (used to be called Georgian wired Polished or GWPP for short… now Pyrosheild Clear) and obscured (formerly Georgian Wired cast or GWC… now Pyroshield Textured) are not only classified as a safety glass but also as a fire rated product, due to the wire reinforcement. The wires will prevent someone falling through it and in a fire the wire holds the glass together, maintaining a fire break.


Read more about the different types of windows...