This method is used in producing synthetic opal. There are three basic stages:
- Formation of suspension of uniform silica spheres of the desired size / colour by carefully controlled mixing of the chemical ingredients.
- Sedimentation of the spheres to produce an orderly packing.
- Consolidation, hardening and removal of excess water, probably by some combination of heat and pressure. The process requires about one year with most of this time being spent in stage 2.
Gemstones produced by this method are:
- Synthetic Opal:
- Synthetic opal has similar physical and optical properties as the natural counterparts. In some cases can be lower.
- Under magnification synthetic opals exhibit characteristic inclusions:
- Lizard skin effect – a regular pattern of the silica gel.
- Columnar growth patterns, when viewed from the side.
- Play of colour effects which are regular and in the same position when the stone is rotated.
- Synthesized by P. Gilson, Russia etc.