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How It's Made

Glass
by

Katie Auckland

on 12 January 2014

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Transcript of How It's Made

Glass
by: Katie Auckland
What Is Glass?
Glass is a hard, brittle transparent material that is mostly comprised of silica sand. Its chemical formula is SiO2. Silica sand has a very high melting point of 1700 degrees Celsius. Its state at this melting point has the consistency of syrup on a cold winters day. A silica molecule has one silicon atom as its center with 1 oxygen atom branching off of each of the 4 corners. Silica is negatively charged and its chemical formula is SiO4. The simplest form of silica has a tetrahedral pyramid shape, which is symmetrical. Silica, in it's crystalline form is Quartz.
Coloured Glass: A Brief History
Early glass received its colour from impurities that were present when the glass was formed. For instance "black bottle glass" formerly found in 17th Century England, is dark green-brown in colour. It was dark due to iron impurities in the sand when it was formed as well as sulphur arriating from the hot coal used to melt the glass. However sometimes glass is purposely coloured by adding minerals and purified metal salts.
Some of the most popular types of glass are Uranium Glass and Ruby Glass.
Invented in the 1930's, Uranium Glass is made by adding uranium oxide. This allows the glass to appear green in colour and glow under ultraviolet light.
Uranium Glass
Ruby Glass
Ruby Glass
Ruby Glass was invented in 1679. When gold chloride was added, it gave the glass a beautiful red colour.
Silica Molecules
Sometimes you may want to remove colour to have clear glass. Whether or not you want it to be dyed a different colour. Decolorizers can be used to precipitate out the sulphur and iron compounds. Manganese dioxide and cerium oxide are common decolorizers.
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Colour
Removing

Colour
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Special Effects
Special Effects
Pressing, blowing,drawing and casting.
There are multiple special effects which can be added to glass that affect its tint and overall appearance. For instance, iridescent glass more commonly known as iris glass, is created by adding metal compounds to the glass to make it iridescent. In addition, this effect can also be produced by spraying the glass' surface with either lead chloride or stannous chloride and reheating it. When the sunlight hits old glass, it can appear iridescent from the reflection striking the different layers of worn out glass.
Iridescent "Iris" Glass
Dichronic glass appears iridescent when viewed at different angles. This effect is creating by placing multiple thin layers of colloidal metal (e.g., silver and gold) particles precipitated in the glass. Dichronic glass can also be made from oxides of metals such as titanium,aluminum or magnesium. this creates the illusion of a particular transmitted colour and a completely different reflected colour. Typically, the metals are coated with either a thin layer of clear glass or quartz to protect it from chipping and oxidization. The finished glass can have anywhere from 30-50 layers of these materials but all the layers together may be about 760 to 890nm.
Glass Pigments
Dichronic Glass
There are 8 factors which are taken into consideration when producing coloured glass:
1. The temperature of the melt/batch
2. The temperature of reheat during working of the glass
3. The duration of the melt/batch
4. The time and temperature rates at different stages
5. The type of colorant being used
6. The concentration of colorant
7. The furnace atmosphere
8. The number of times the same glass is melted. The more times it is melted, the darker the colour in the finished product.

The same element but in different compounds will cause different colours. For example, when iron oxide (FeO) in the form of ferrous iron is added, the glass will have a blue-green tint. However when the iron is at a state of higher oxidation, such as ferric iron, a yellow-green tint it produced. Small amounts of sodium nitrate is added to batches to ensure that any iron impurities are in its ferric state.
Properties of Glass
Glass is a hard, fragile substance. Most often it is found in a transparent form. It is mainly made up of Sand, soda ash, and limestone which bond together at high temperatures. They are cooled rapidly and form the crystalline-like substance we know as glass.
In its solid state glass, is non-malleable. It is brittle near its freezing point and soft near its melting point. Different types of glass melt at different melting points. Some have a melting point as low as 500 degrees Celsius and others at 1800 degrees Celsius. Standard soda lime glass has a melting point of around 1500 degrees Celsius.
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In conclusion, glass itself has changed over time. There are now more efficient ways to produce it. Colouring glass is an art that has been around for centuries. However using silica sand to make glass has been a ingredient that will stick around for years to come.
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