Glass or Paste

Glass or Paste

Natural Glass
Just to confuse matters, there are a number of natural glasses such as obsidian, which can be classified accurately and undisputably as a gemstone. Natural glasses can originate from volcanoes or meteorites.

Synthetic Glass Gems or Paste
When glass is used as a gemstone simulant it is known as paste. The ancient Egyptians used coloured glass as gemstones, and it is still used today in costume and fashion jewellery as an inexpensive but reasonably effective imitation for more expensive gemstones. Paste stones are often foil backed to reflect more light, the foil sometimes being coloured. Other reflective coating have been used including mercury amalgam in Bohemian paste stones.

Colours of Glass
By "doping" with different minerals, many different and attractive colours can be produced. The best known, and commonest is colourless, usually referred to as white.
Cerium oxides, CeO₂, Ce₂O₃, produce red orange and yellow.
Copper, CuO, Iron, Fe₂O₃, Nickel, NiO, Praesiodymium, Pr₂O₃, and Titanium, TiO₂, oxides all produce yellow amber and brown.
Erbium, Er₂O₃, Europium, Eu₂O₃, Holmium, Ho₂O₃, oxides produce pink.
Chromium, Cr₂O₃, Thulium, Tm₂O₃, Vanadium, V₂O₃, oxides produce olive green.
Cobalt, Co₂O₃, Manganese, MnO₂, Neodymium, Nd2O3, oxides all produce lilac and violet.

Technical Information
Common glass is made from sodium silicate, but a large variety of silicates can be used. Other additions give rise to many specialised glasses.

Chemical Composition and Name	SiO2 - Silicon Dioxide
Hardness	usually less than 6
Refractive Index	1.44 - 1.90
Specific Gravity	2 - 6
Crystalline System