Cutting and carving opal
Opal is 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. The opal has to be kept wet and cool while it’s being cut, so it doesn’t overheat and crack.
Cutting opal is a very skilled job – especially in the case of Lightning Ridge nobby opal, in which the gem colour may be distributed in almost any way imaginable within the potch of the nobby…as may inclusions of sand, or occasionally gypsum. The classic nobby structure comprises a horizontal bar of gem colour on a base of (preferably black) potch, usually also with a cap of potch on top of the colour bar; but the exceptions are far more numerous than the rule. It takes a great deal of experience, cutting material from many fields, to be able to accurately ‘read’ nobbies – and in most cases, not even the best opal cutter in the world can predict whether a nobby will ‘cut’ until they have begun to rub it down on the wheel.
Seam opal is (generally) more straightforward for the cutter – though it, too, can offer many challenges! The gem opal colour sometimes occurs in a thin bar; indeed, sometimes the bar is literally paper-thin. If the surface of the bar also undulates, the piece cannot be cut using traditional cabochon techniques without losing much of the colour. In this case, the piece may be cut and polished with hand-tools to produce an undulating surface. This is done most frequently with Queensland boulder opal, in which brilliant gem colour may be whisper-thin, in or on the dark ironstone that helps to make this form of opal so spectacular. In recent years, undulated surfaces have been produced more frequently in other forms of opal also, to produce unique pieces and to make best use of the precious material.
Carving opal takes the principle of the undulated surface a step further, treating the rough opal as a three-dimensional object rather than limiting its potential to one gem-coloured face. The guiding principle of opal carving is not to impose a predetermined shape on the rough opal, but to observe the opal carefully, and be guided by it. The carver removes surface sand inclusions, fractures and any other flaws, then seeks to create a beautiful object, making best use of the natural shape and play of colour in the piece and seeking to conserve the precious gem colour. Opal is carved using an electric hand tool that looks like a dremel or a dentist’s drill, with fast-rotating diamond-coated tips on the end.
Armani Pacifica was carved from a nobby mined at the Coocoran opal fields near Lightning Ridge, Australia.
- The rough nobby. First step: remove bulk surface sand and determine the extent of a natural cavity (green arrow).
- Cleaning the surface revealed internal sand at three levels, being deepest on the left (red arrow). The cavity turned out not to be deep (green arrow). A curved natural fracture (white arrow) gave Daniela her first thoughts of creating a round shape in that area.
- Sand was removed near the red and green arrows and steps created. In some places, although sand was still visible through the surface (e.g. at yellow arrow), transmitted light showed that it could not be removed without destroying the integrity of the piece, so Daniela chose to leave it. The round recess was accentuated (white arrow) as more sand was removed. On the right end, Daniela carved grooves and added steps to emphasize contrast between the dominant blue and adjacent opal with little visible colour or pattern. Some sand remained on this end (pink arrow).
- Chasing sand from the round recess produced an unattractive flat area, so Dani enhanced the shape with little loss of material by forming a spiral (white arrow). On the right end, further emphasis of grooves and removal of sand resulted in lifting pale amber potch to reveal a rich, dark water bar (pink arrow). Similarly, eliminating sand beneath the green arrow unveiled rich blue on a dark core. Polishing the piece made sand beneath translucent windows more visible (yellow arrow) but the intensity and brightness of gem colour overwhelms what may otherwise have been considered a flaw.
“I hated this piece at the beginning and loved it at the end,” said Daniela. “It wasn’t until between stages 3 and 4 that I found the shape and started to love the piece.” “Sometimes, you can feel overwhelmed and like you’ll never find a solution; then you go back another time when you’re more relaxed and BANG – you find a shape that works.”
Opal cutting courses are taught at the colleges of Technical and Further Education (TAFE) in Lightning Ridge. If you cannot access those courses, try to find a lapidary club that runs cutting courses – any basic lapidary skills are a good pre-training for cutting and carving opal – and seek out an experienced opal cutter or carver who will teach and mentor you. Opal can be a heartbreaking gemstone to cut, but the joy of seeing those incredible opal colours emerge, together with the constant challenge and the excitement of discovery, make opal cutting a joyous (even addictive!) pursuit.