The answer to this question is BOTH!
Naturally occurring glass is known as obsidian. Our curious and inventive ancestors tried to mimic what they saw in nature. They noticed that sand melted when it was put near the fire and liked the results. Centuries of development later has resulted the glass you use today.
So how is glass made nowadays?
To make glass you will need the following ingredients:
Calcium Oxide (from limestone)
Lots of heat!
To obtain different effects, such as colour, you can use one or more of the following options:
Cullet (recycled glass – see below in Recycling Section
Magnesium or Aluminium oxide (can be used in place of Calcium Oxide)
Lead (if you want to make crystal glasses)
Boron (to change thermal and electrical properties)
Lanthanum Oxide (if you need enhanced light reflective properties)
Iron (to absorb infra-red energy)
Colour (change the colour by adding various metals or oxides)
Coatings (you may wish to coat your glass to give it a special finish.)
Lots more heat!
1. Heat your ingredients to 1,500 – 1,600 Deg C and cook for up to 50 hours.
2. For float (sheet) glass, allow the molten glass to flow onto a layer of molten tin. Add any coatings you may wish to use and allow to cool slowly in a lehr.
3. For containers and drinking glasses, firstly make a “parison” or pre-form (thick miniature bottle shape) by pressing or blowing a blob of molten glass (called a gob) into a shape using a mould. Put the pre-form into another mould and use compressed air to push the sides out and into the shape of the final bottle or glass. Cool, re-heat and allow to cool again (this prevents breaking).
Don’t try this yourself at home!
Glass is a great material to recycle – it can be re-used again and again. It saves mining for the raw materials and it requires much lower temperatures.
When you send your glass to be recycled, it will be cleaned, sorted into colour and processed to remove any impurities. This will leave “cullet”. This is added to the raw ingredients where it quickly melts and is added to the mix.
So now you have a brief knowledge of how glass is made!
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