Opal Lesson
Australia produces 97% of the world’s opal. 90% is called ‘light opal’ or white and crystal opal.  White makes up 60% and all the opal fields produce white opal; Crystal opal or pure hydrated silica makes up 30%; 8% is black and only 2% is boulder opal. White opal is simply crystal opal with magnesium oxide in it and black is with iron oxide in varying degrees of darkness.

By comparison opal is at least fifty times rarer than diamond, and only occurs in Australia (3% of opals are found throughout the rest of the world).

Opal does exactly what a rainbow does.  It splits white light into the colours of the spectrum through a diffraction grating, and just like a rainbow with a black storm cloud behind it, a crystal opal will also look better if it has something black behind it too.  That’s why we use crystal opal to make “doublets” and “triplets” and why we use crystal opal to make opal in-lay jewellery where we blacken the base of the setting with a black paint and then set the crystal opal on top of it.  This acts like a storm cloud behind a rainbow, enhancing the rainbow colours.

White and crystal opals give us yields of 50% with a 50% loss factor while the much lower yield on boulder and black opal is only 5% with 95% loss.  This makes boulder and black opal far more valuable.  In fact the prices increase in a mathematical progression:  1, 2, 4, 8 (the price for black opal is at least 8 times more than the price of white opal).

When evaluating an opal, there are three factors we look for which are important and add value to the opal:

1. The colour is multi-directional; you can see it from all angles

2. The colour is in a large, ‘blocky’ pattern which is better than a fine pin fire pattern; and

3. The opal has a strong fire.  By this we mean that when the opal is in the shadow it will still flash colour.  The fire is really the most important factor in valuing an opal.  The most valuable fire is red fire, followed by orange, yellow, green, blue, indigo and violet. 

Boulder opal is the rarest.  Only 2% of the opal mined is boulder opal.  It was the first commercially mined opal discovered in Australia and will be the first opal to run out.  Where there is opal mineralization it fills up the cracks and the crevices of the ironstone country of southwest Queensland.  All opal is a diminishing resource and boulder will be the first to run out.  The cost of Government required rehabilitation of mining leases and the difficulties inherent in Native Title Legislation will help see to that. 

The relative prices of opal go like this; if a triplet is valued at $1.00 then the same weight, colour, pattern, shape etc in the others would be valued as follows: doublet $2.00 (gilson also $2.00), white opal $4.00, crystal opal $8.00, boulder opal $16.00 and black opal $32.00, ie a black opal that looks like a triplet opal would be approximately 32 times the triplets price.

With our doublets and triplets, we never use plastic on the base because plastic has a different coefficient of expansion to opal and will delaminate from the opal as it expands and contracts at a different rate to the opal.  So we guarantee that our doublets will never delaminate and we offer a lifetime guarantee.  Doublets and triplets do a great job duplicating black opals at a fraction of the price.

Triplets are just doublets with a thinner layer of opal capped with quartz crystal (silica dioxide) so again we have three silicates together and the same lifetime guarantee applies against delaminating, so they will never lose their colour.  The quartz crystal cabochon on top does three things for the opal –

1. It is domed so it acts as a lens to magnify the pattern of the opal

2. It has a higher refractive index than the opal so it kicks up the colour of the opal; and

3. It is harder than the opal and it protects the opal.  So at 1/30 of the price of a black opal, it does a very good job duplicating a black opal.

The relative prices of the different types of opal go like this (from triplets to blacks) 1, 2, 4, 8, 16, and 32.  A black opal is 32 times the price of a triplet as a rough rule of thumb.

Gilson Opal Lesson
A synthetic gemstone is defined as having ‘essentially the same optical, physical, and chemical properties as the stone named’. 

Both the Gemmological Institute of American (GIA) and the Swiss Gemmological Institute (SSEF) in Basel, Switzerland, have identified Gilson and similar opals as synthetics in lab reports for years.

If a material fulfils the criteria for synthetic opal, [i.e.] it has essentially the same physical, optical and chemical properties and, when checked, shows the same type of structure as natural opal, it would be identified as ‘synthetic’ opal.  If it has been treated in some way, such as dyed or impregnated, or if the material is assembled, treatment is disclosed in the conclusion.  (GIA representative)

If you wish to see what Gilson opal looks like, we are happy to show you.  Be aware also that much in-laid opal and many opal doublets and triplets are made using synthetic opal.  We will never sell you a Gilson synthetic opal unless you request it and unless we disclose it.  All of our gemstones are sold with valuation and authentication certificates.