Diagram of the overall bottle production process
Diagram of the furnace
The Doghouse - opening through which the
raw materials are fed into the furnace
Diagram of the glass forming process
Gob of molten glass about to be moulded
Colours in Glass
Unless the raw materials are very pure, glass made by mixing and heating sand, Soda ash and limestone will normally be green, the depth of the colouration depending mainly on the amount of iron oxide and other colourants present in the raw materials. A sand containing as little as one thousandth part of iron oxide will give normal soda-lime glass, used for windows and glass containers, a greenish tint.
For many products, instead of using high purity (and thus expensive raw materials, glass manufacturers may decolorise the glass by adding minute amounts of other colorants which produce complementary colours to green so that the finished article appears colourless. Thus selenium ( which gives a pink colour) and cobalt (which gives a blue) can be added to soda-lime glass to offset the effect of the green or yellow due to the iron and this is done in the manufacture of glass containers. Nickel may be used similarly in the decolourising of lead crystal glass.
Different additions may produce different coloured glasses, the range of possible colour being almost infinite. Some of the most frequent used colourants and the colours they produce are listed here. The colour often depends on the state if oxidation of the colourant, the type of glass in which it is used, and thermal treatment.
Colourants
Iron Green, Brown, Blue Manganese Purple Chromium Green, Yellow, Pink Vanadium Green, Blue, Grey Copper Blue, Green, Red Cobalt Blue, Green, Pink Nickel Yellow, Purple Uranium Yellow, Brown, Green Titanium Purple, Brown Neodymum Purple Praseodymium Green Cerium Yellow Carbon and Sulphur Amber, Brown Cadmium Sulphide Yellow Antimony sulphide Red Selenium Pink, Red Gold Red