"Nature's Fireworks" - A Beginner's Guide to OPAL - Part 4 M

By:Stuart Bazga

Individuals rather than large mining companies do mining in the Australian opal fields. The reason for this is that opal is particularly elusive; it is not found in great amounts at a particular level or in a particular area, but is found at varying depths beneath the surface and is usually found at levels up to 25 metres deep.
Although in reality all that is needed to get started mining opal is a pick, most miners now consider a jackhammer and an electric hoist – a machine used to get opal-bearing dirt to the surface – the minimum equipment needed. Most shafts are now drilled using a drilling rig. After a shaft has been sunk and the opal level identified, horizontal drives are dug.
After bringing the dirt to the surface, it is initially processed by washing away all the ordinary dirt and leaving behind potential opal stones. This is usually done in an “agitator,” a modified stationary cement mixer. Water is pumped through while the dirt rotates inside. Sludge pours from the mesh-covered openings in the side of the agitator as the dirt is washed away. What remains are known as tailings.
This final process is either the most exciting or disappointing part of the hard work of opal mining. It is at this point that it becomes apparent how much, if any, opal there is among all the dirt that has been mined.
Sinking a Shaft:
This is one of the most effective ways of finding opal, but also the most laborious. The length of the shaft can be as short as three meters or as long as twenty.
A variety of tools are needed, including a hand windlass or motorised winch that is placed over the hole, lifting the dirt to the surface. Some miners will use an expensive vacuum-cleaner apparatus called a “blower.”
Once the bottom of the shaft has been reached (where the opal-bearing dirt begins), the miner begins gouging away very slowly. A horizontal tunnel is dug in the hope of finding a seam of precious opal or scattered “nobbies.”
Puddling and Rumbling:
This technique is used once the opal dirt has been transported away from the surface, usually by trucks. The dirt is first placed in a large mesh-lined drum. Water is pumped through it as it rotates, turning the dirt into sludge.
The sludge escapes through the mesh in the sides, leaving only pieces of rocks, and hopefully opal.
Open-cut Mining:
Open-cut mining is created by running over a large area of ground with a bulldozer, slicing away the dirt until the opal level is reached. Although this method is very expensive, the chances of finding opal are increased as a larger area can be mined at once.
Noodling: Noodling is when a person goes over what other miners have rejected as rubbish. All that is needed by a “noodler” is a sieve and a very keen eye.
PROCESSING
Unprocessed opal straight from the ground is known as “rough.” The miner may sell it at this stage, or he may choose to continue the processing himself. Although the potential value of the opal can be estimated while the material is unprocessed, its actual value cannot be established at this stage. The rough opal, although it may look as if it will cut well to produce valuable stones, may have faults within it. Conversely, an ordinary looking piece of rough may produce a magnificent gem. The choice of selling “in the rough” or continuing processing belongs to the miner.
Cutting:
Cutting and polishing is the process by which the opal is completed before setting into jewellery. A “rub” is stuck onto the end of a “sop-stick” – a short piece of thin dowel used as a handle - with jewellers wax. Using a fine grit cutting wheel, and holding the stone with the dop-stick, the stone is shaped and flaws and scratches are removed from the stone.
Polishing:
The stone is then polished, usually on a leather wheel using jewellers polishing powder. Careful attention is paid to achieve the best possible results, taking into account the appearance of the stone and retaining as much of its size and weight as is compatible with all other factors. With each touch of the cutting wheel, the cutter will reassess the stone, checking the appearance and colour as well as the presence of any faults, making sure that the maximum potential of the stone is achieved.
Oval-shaped stones are still the most popular, but some times, to achieve this shape, a lot of good opal may have to be cut away. In order not to grind away fantastic colour that nature has taken millions of years to produce, an opal may be left in the shape in which it was found. These stones are called “free-forms,” and are becoming more popular as people realise how individual, personal and attractive these unique stones look once set in jewellery.
CARING FOR YOUR OPALS
Opal is a very delicate gemstone and it is important you properly care for it. Although solid opal does not require any special conditions, it is advisable to avoid impacts and knocks. Keep it away from direct heat and sunlight, and avoid accidental splashes with any chemicals.
Opals are softer and more fragile than most other crystalline gemstones. Be careful not to scratch or hit opals, especially those mounted in rings, and avoid wearing rings while washing up or doing gardening and housework.
Never clean your opal with jewellery cleaner of other harsh chemicals. Simply use water with a little vinegar in it and brush the jewellery gently with a soft toothbrush, then rinse in clean water. Contrary to some belief, water will not harm solid opal. In fact, it is sometimes recommended that solid opal should be immersed in water overnight occasionally to maintain its water content, a recommendation that may or may not be true. However, doublets and triplets should never be immersed in water, as moisture may get in between the layers, spoiling its appearance or causing the glue holding the layers together to dissolve.
Opals are composed of between 3% - 20% water and as such, should not be allowed to dry out or freeze.
When storing opal, avoid using plastic bags and dry storage conditions. Soft cloth bags with padding are ideal. If storing solid opal, take it out occasionally and wipe with a damp cloth or dip in fresh water.
That concludes part 4. In part 5 we learn about the types and characteristics of some of the major types of opal available today.
So unitl then,
Best wishes and have a great day
Stuart Bazga
www.kulpunyaopals.com

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Article Source: http://www.articles2k.com

Kulpunya Opals was established several years ago to provide the UK and Europe with a specialist supply of opals at great prices. We import directly from key suppliers in Australia with whom we have developed strong and long-term relationships. This ensures the products are always of the highest quality, and each represent excellent value.

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