Back when the first commercial opal mines were dug, the operation was extremely simple whereby the miner would dig a vertical shaft down until it reached the ‘opal dirt’, and at that level, horizontal shafts were dug. The ‘levelling’ as it is known was carried out by pick, shovel as well as explosives and the loose dirt was removed by bucket and raised to the surface via a windlass.
Modern Opal Mining
Fast forward to today, and the process is similar, expect there is a great use of mechanised tools for digging, extracting, lifting, and sifting. The old windlasses have been replaced by power winches and also automatic bucket tippers. For larger mines, a blower is often used which is like a very large vacuum cleaner that literally suck the clay-stone to the surface.
Most vertical shafts are now sunk using a Calweld drill to drive a 1m diameter hole down to the desired depth. There is no exact science to where the shaft should be sunk, nor how deep the levelling should as the optimum level can vary from field to field and region to region. In Lightning Ridge, the optimum level for bottoming out (the depth of the main vertical shaft) is between 138-143 metres above sea level.
There are two forms of opal; Precious or Common, also called Potch, which does not display the ‘play of colour’ of precious opal and is of the one, dull colour.
Miners will hope to find a seam of ‘potch’ that can be followed in the hope it will lead to precious opal, but these seams can dramatically change direction vertically and horizontally; and often can just stop. Along the way, these seems can also reveal opalized fossil from the era of the dinosaurs.
Since the 1970’s, many mechanised innovations have been introduced including ‘boggers’ (small underground front and loaders), as well as auto hoists and revolving cutting heads. These ‘tools of the trade’ have dramatically increased the output of mines.
From there, the opal bearing material is taken away for processing, either ‘wet’ puddling or ‘dry’ puddling.
Wet puddling is the process by which the opal dirt is rinsed within an ‘Agi’ (agitator) to release the opals for the dirt. The Agi is the rear-end of an old cement mixer and is placed somewhere near a water supply/dam. With the opal dirt put in the rotating agitator, water is pumped in removing the finer particles from the large material, with the finer material sent to a sediment dam. The larger material is collect in a tray for hand sorting.
Dry-puddling is similar, but instead of water, mechanical action is used to separate large from small. A lot more rudimentary than wet-puddling, this method is much less efficient but is often used as precursor to wet-puddling.
Over the border in Queensland, mush of the opal mining activity centres around open-cut mining, whereby overburden (the top soil) is stripped away to reveal the layer/s of ironstone of which the boulders are removed for processing.
From there, the rough opal is sent off for either processing and then sold, or sold in its rough form.
Opal Cutting, Polishing & Mounting
The next process before the stone becomes presentable for sale either just as a stone or integrated into a piece of jewellery is the cutting and polishing.
The opal is purchased by the opal jeweller or store either directly from the opal miner or buyer (someone who purchase opal and on-sells it), and like any form of good business, strong and trusted relationships are built up over years so the artisan or store can offer people the best possible specimen.
The opal is generally sold as a ‘rough’ or rough cut opal that is still pretty much in its native state but has been cleaned up a little. The purchaser will look at the stones in terms of its characteristics and how best it can be further cut and polished to the ideal shape to best highlight the stone in an envisaged setting.
The jeweller will often wet the stones in order to highlight the characteristics of the stone (colour, hues, brightness, fire, etc) before selecting a stone for further cutting and polishing.
Some larger stones can be handheld, but most stones are too small to safely hold by hand for the finer work and so they are mounted on a dopstick. Traditionally, the ‘rough’ is held to the dopstick by wax which is melted over a candle then applied to the top of the stick before being adhered to the opal. Use of the wax means the dopstick can easily be removed from the opal without any contamination or remnants that might occur if a glue or adhesive was used.
With the ‘rough’ on the dopstick, the process of cutting and polishing can begin with the later a progressive process through several different polishing stages/grades (coarse to fine) to achieve the best shape and balance for the particular stone.
With the polishing process finished the stone will then be incorporated into a piece of jewellery; there is every chance that even at the ‘rough’ stage the jeweller knew what setting and type of jewellery would best highlight the qualities of the Opal.