Page 11 - Curriculum Visions Dynamic Book

(Right) The need for glass shades on oil lamps helped stimulate the development of borosilicate glass.
Glasses manufactured by these methods tend to have a natural green tinge due to the presence of iron impurities in the sand used for the silica. If required, the tinting can be counteracted using a small amount of a decolourizer chemical. Selenium oxide (SeO2), cobalt oxide (CoO), arsenic oxide (As2O5), and sodium nitrate (Na2NO3) are widely used for this. The result
is a glass without any colour sheen – so-called white glass.
Soda lime glass and its variations are clear enough for windows and many other purposes, but the glass does not sparkle. However, a sparkle can be added by using lead monoxide (PbO) as
a flux. Such a glass is heavier than soda glass;
but when cut properly, it can be used to make extremely attractive table glass.
Giving glass special properties
Colouring glass
Because silica combines readily with metal oxides, they can be used to colour glass. Typical oxides and colours are purple-blue from cobalt, green or yellow from chromium, yellow from uranium, and violet from manganese. Ferrous oxide (FeO2) produces a green or a blue colour, but it varies with the chemistry of the glass. Ferric oxide (Fe2O3) yields yellow glass. Lead oxide (PbO) and silver oxide (AgO) also add a yellow colour. Nickel makes potash-lead glass violet but turns soda lime glass brown. Copper produces blue or green colouring depending on the amount of copper oxide.
(Right) Coloured glasses are used for decoration in many modern buildings.
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