Natural Opal is a form of silica similar to quartz but containing water within the mineral structure. Precious Opal consists of small silica spheres arranged in a regular pattern. The colour in precious Opal is caused by diffracting white light which breaks up into virtually all the colours of the rainbow.
Cultured blue opals from Japan
In 1974 a Frenchman by the name of Pierre Gilson discovered a way of culturing genuine blue Opals with all the properties of a natural Opal apart from the presence of water. The process takes over 12 months to create a real Opal almost identical to those being mined. The advantage of Gilson's Opal is that it tends not to crack in the way that natural Opal may do if it loses its water content due to extreme temperature changes.
The Japanese have also discovered how to 'culture' the most beautiful fiery, blue Opals using a form of quartz silica and zirconium oxide. They are initially formed in much the same way as Gilson's but are then impregnated with polymer as a stabilizer ensuring that the silica structure is completely cemented together and the vivid play of colour in the Opal is therefore permanent. These man-made Opal gems have very similar physical properties and chemical composition to natural Opal. They display fiery blue colours with flashes of green or turquoise which are truly breathtaking! Indeed a natural Opal of similar colour and quality would be unaffordable for most and so we are pleased to include cultured blue Opals in our latest jewellery collections. It is important to point out that these are a genuine form of Opal and not to be confused with cheap imitations available in the market today.
Cultured blue Opal Gem Specifications:
Gem Type: Cabochon cut polymer stabilised Opal
Colour : Light blue with turquoise flashes.
Clarity : VVS Fine quality
Treatment : Lab Created AAA Gem Grade
Specific Gravity : 1.89
Where do most Opals come from?
Over 95% of the world's natural opal is found in Australia. The town of Coober Pedy in South Australia is a major source of opal. Another Australian town, Lightning Ridge in New South Wales, is the major source of black Opal. Black Opal is so called because it has a predominantly dark background displaying a vibrant play of colour.
Whether an Opal is 'black' or not can be determined by ignoring all colours and concentrating only on the overall body tone (background blackness level) of the Opal. When this is compared to the scale of blackness given below it is possible to identify how black the stone is.
Only Opals achieving values N1 to N4 on this scale are considered black Opals - attracting the additional value associated of this class of precious Opal. N5 to N6 would be classed as semi-black and may still be considered fine Opals displaying excellent colours.
Boulder Opal gets its name from the fact that an ironstone backing is part of its natural formation. The colours can also be extremely bright and vivid. Gem quality boulder Opal can be very expensive competing in price with some black Opals.
Fire Opals are yet another type of Opal. They tend to be transparent and are found with a warm body colour ranging from yellow to orange. They do not have the 'play of colour' associated with other types of opal and look completely different. The most famous source of fire opals is Mexico. Hence these Opals are popularly known as 'Mexican Fire Opals'.
How do you value Opal jewellery?
most important criterion for determining the price of an Opal is the play of
colour, the colours themselves and their pattern. If the colour red appears
when looking through the stone, all the other colours will appear also. For
evaluating Opals the thickness of the Opal layer is considered, the beauty of
the patterning, the cut, weight and finish. The following factors should all be
taken into consideration:
- The colours present in the opal (also called
"play of colour").
- The brightness of the Opal - called the
- Whether the Opal is black, dark, boulder or light body
- How saturated or intense the colours are in the Opal.
- Whether the Opal appears
dull from any angles.
- Whether the Opal is flat on top or has a rounded dome.
- The size and weight of the Opal.
- The cut of the Opal - even oval, or
irregular free form.
How should I look after my Opal jewellery?
- Avoid extreme
changes in temperature that could cause opals in your Opal jewellery to
- Avoid knocking
or scratching Opal jewellery. Remove your opal
jewellery when playing sport or gardening. Never wear your Opal jewellery when carrying out household tasks like
washing dishes or using chemicals or cleaning agents.
- Clean your Opal jewellery with a gentle detergent in warm water using a soft cloth or brush. After cleaning your Opal jewellery should be rinsed in clean water to remove any residue.