This is any glass used for windows and encompasses plain plate glass and glass used for double glazing units. Generally we need window glass to be strong, safe and keep the heat in or out. The glass used in most windows these days is tempered or safety glass, this means that when it is broken it does not break into a few large sharp pieces, but many smaller pieces that are held together. This increases our home or car security whilst making it safer if children fall into it. To keep heat in or out requires the use of double glazed units or using a window glass film which can help to reduce the amount of sunlight coming into the house.

Making Window Glass

Did you know that glass making has been around for over 4000 years and that we could make really fine glassware long before we could make good windowpanes? High quality table was being made around the year 0, but even in medieval times glass makers were struggling to make clear flat glass. The first window panes were made by blowing glass and flattening it – this left the traditional mark in the middle of the pane that we associate with antique window glass. Later the glass was blown into a cylinder shape, opening and flattened. Another method was crown glass, where molten glass was spun from a central point and spread out. This resulted in glass that was not completely flat hence the term crown glass – the glass was thicker in the center. Plate glass was developed by the French by using a mold, when the glass was cold it was ground and polished until flat and smooth. Mass produced window glass did not appear until the early 19th century, when the process of rolling molten glass was mechanized.

There are many different types of window glass and many different uses. We use glass in houses, office cars, cubbies and more.  Some types of glass are found to have specialized applications. If you are considering replacing window glass it is worth knowing about the options you have.

Float glass –made by floating molten glass on molten tin, they do not mix, but a flat surface exists between the two as the glass starts to cool, then the glass is annealed( a controlled cooling process) . This is the standard glass window pane, often called annealed glass.  Many other forms of glass begin with float glass

Laminated glass – two sheets of glass glued together often with a PVB plastic or resin. Used as a security glass. Laminated glass is no tougher than annealed glass its benefit comes from the fact when broken the glass hangs together by the glued layer making it safer when broken.

Tempered glass- also called toughened glass and is about three times as strong as standard float glass. Thermally toughed or tempered glass is stronger than annealed or laminated glass, it takes more force to break the glass and although the glass will not hang together the pieces tend to be small.

Laminated tempered glass gives the best safety solution, being much harder to break, breaks into small pieces that hang together making it safer. Often used for auto window glass.

Anti reflective glass- standard float glass coated with metal oxide that allows a small amount of light to be reflected.

Tinted glass- during the floating process, chemicals are added to the glass which change the color and help to minimize the amount of sun to pass through the glass. Tinted glass colors vary and include purple or pink.

Electro chromatic glass- sometimes called smart glass where the glass is coated in a thin layer that will change color when an electric current is applied to it. This means the glass will darken when the sunlight increases. Very cool effect and useful for glass building to be thermally and light efficient.

Fire resistant glass- the main types – heat transmitting or fire insulating. Heat transmitting – is able to contain the e fire for a short time, and the glass gets hot – usually laminated glass reinforced with wire . Fire insulating also contains the fire for a time longer than heat transmitting, and also contains the heat.

Alarm glass- security glass laminated with wire between the glass sheets. The wire is connected to a power supply and any damage to the glass sets off an alarm.

Low E glass – an energy efficient glass, also called low emissivity glass. The glass has a coating of metal oxide to retain the heat in the house. Used in sealed double glazed units as the coating is soft and prone to damage. A double glazed unit which has a low emissivity window coating on it is twice as efficient as a typical double pane.

Patterned glass- patterns are made during the rolling process where the glass is flattened and the pattern applied to one side only. The pattern will determine the amount and quality of light to pass through.

photo courtesy www.garrisonphoto.org/sxc

photo courtesy www.garrisonphoto.org/sxc

Reflective glass- a metallic coating is applied to float glass which gives it a mirror effect – this glass is also known as mirror glass and reflects the light and helps to provide privacy

Self cleaning glass- this is a very cool kind of glass. Float glass is coated with a chemical that when the sun’s rays hit the glass a photocataltyic reaction takes places and the dirt on the glass is dissolved and when it rains the dirt is washed away. This glass is more expensive than standard float glass by 10-20%, but that maybe more than compensated by the savings in window cleaning – especially useful for high or inaccessible windows.

With all these different kinds of glass it is apparent that choosing glass for your home is not straight forward. You should consult your local glass merchant for advice – be sure to check their credentials before you accept their advice. A window glass supplier of one year may not provide the same advice of one of 10 years business. Window glass installation can be carried out by the competent handyman or the professional installer.
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If security is your main concern with existing windows then window glass film may be worth considering. A good window glass film will be strong, tear resistant, transparent and have a good adhesive to attach it to the window – expert installation recommended to get the best result.  There are many different styles available including stained glass window film. These help to keep the glass together when broken and can also provide privacy to you home at a much lower price than replacing all your windows glass.

Category: Windows
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