Ceramic Techniques

A ceramic is basically:

A finely ground inorganic powder.
Which maybe heated, fired or sintered.
Sometimes compressed to produce a polycrystalline solid.
In some cases, a binding agent with a low melting point is used to hold the particles together.
The surface maybe glazed.
In all there are three main stages - grinding, precipitation and / or compressing.
Most of the ceramic products are not true synthetics since they do not have the exact chemical composition of the natural product which they simulate.
Constituents used might be powders of the natural substance itself (reconstructed) or totally different chemicals.

Gemstones made by this method are:

Lapis Lazuli: (Gilson) Available with or without pyrite, lower S.G. of 2.46 and lower hardness of 4.5. Very even surface texture.
Turquoise: (Gilson) Available with or without matrix, slightly porous, under magnification dark blue particles observed in a white background.
Coral: (Gilson) Smooth texture, lack of pores and tree ring structure, lower S.G.
Jade: (General Electric) Initially made in 1984, but has not been commercially produced.
Yttralox: Used as a diamond simulant, is transparent, hardness is 6.5, R.I. of 1.92, dispersion of 0.039.

Organic Gemstones

Inorganic Gemstones