Cutting and polishing Australian opals is a specialised skill presenting many challenges to maximise the end size and colour of the precious gem..
Allgem opal cutters assess stone material to determine the potential ability to develop it into a gem quality stone, suitable for jewellery. Some precious gems or gemstone rough is best left that way it is due to natural flaws, non-uniformity of colours, and poor saturation of colour.
Joseph Gryg has been cutting Australian opals for almost 60 years and Allgem cutters are widely recognised as Australian opal and jewellery experts.
The precious gems are cut on a series of lapidary wheels with fast-moving, diamond-impregnated belts. The cutter starts with a belt that has a relatively coarse surface (e.g. 250 grit), then moves along a series of belts with increasingly fine surfaces, finally creating a polish with a very fine abrasive compound loaded onto either felt or leather.
Australian opal has to be kept wet and cool while it's being cut, so it doesn't overheat and crack.
The face of the stone is shaped into a cabochon (dome shape) and the overall shape is decided depending on the stone (most cut opals hold greater value in an oval shape).
The back of the stone is cut on the same set of grinding wheels, this time producing a flat bottom, and an edge which tapers up to the 'girdle'. The shaping of the girdle is an important and difficult part of cutting, and refers to the point on the side of the stone where the two top and bottom edges meet. This edge is used by jewellers to set the stone underneath gold, to provide a safe and secure setting.