Recently at an Opal Show I met an Opal Wholesaler who took some Welo Opal to the United States of America from Australia. He placed some Ehtiopian Opal in his carry bag and some in his check-in luggage.
When he arrived in USA he noticed the opals in the check in luggage had some cracks on the surface but the opals he hand carried were in fine condition.
So it seems that the atmospheric pressure or humidity change had an influence on the Hydrophane opal?
Checking atmospheric pressure we find most jet airplanes have controlled pressure in their luggage compartment but most are not heated and are just above freezing. Even pressure in older aircraft might not be as accurate as airline companies report.
I don’t think anyone has studied the effect of atmospheric pressure or humidity change on Welo Opal. If diamonds are formed by natural pressure there is reason that Hydrophane opal could be affected by atmospheric pressure.
For air travelers pressurization becomes necessary at 12,500 feet or 3,800 meters. We are all familiar with the pressure in our ear drums caused by rapidly descending aircraft or even altitude sickness. Many have had the experience of fizzy drink bottles exploding in their cases or shampoo bottles exploding in check -in luggage. Apparentlyif the shampoo bottle is not full it will not explode.
This makes us wonder about water in Hydrophane opal as it has nowhere to go when under pressure and if opal freezes as the aircraft rapidly descends into dryer humidity’, this might affect the opal?
Animals are shipped in luggage compartments that are heated and pressurized but airlines have different compartments for luggage. Most luggage compartments are not heated and sometimes your luggage will arrive freezing cold and what happens to this opal when it arrive in dry humidity?
Gemstone cutters have done fracture testing on quartz for centuries. Even in 16th century German, they would pressure- test quartz by placing hot or cold water or ice to fracture test quartz. Then the fracture would crack at its weakest point and they could carve and shape the rock without fear of any more cracking.
Maybe air travel is doing the same to some hydrophane opal? So many factors can effect hydroplane opal. It might only be small proportion of opals that would be affected but worth investigating. Most International flights fly at 39,000 feet or 12,000 meters
You can’t really put moisture in a baggie with Welos because they will absorb it and it will alter their appearance, and the water alone could crack the opal by absorbing unevenly, even before it gets to the cabin pressure or temperature issue. Most rough is bone dry, and gets flown out of the country at some point, so I wouldn’t think cabin pressure would make much of a difference unless a cut opal still had water in it. Freezing should also only affect it if it has water in it that would expand when it froze, so drying Welos thoroughly is a must.
In the end, we are unable to find a definitive reason as to why Ethiopian Welo opal is affected by air travel.
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Update September 2016
This article was written three years ago when there were problems with Ethiopian opals cracking.
But today it is not so much of a problem
Ethiopian is much more stable today due to many factors
Around 5 years ago opals were mined closer to the surface and were less stable.
Indian wholesales who controlled 80% of the export market would soak the rough and cut stone s in oil ,but today this is not standard practise
They would even place opals in oil, dry off and export the opals.
Now nearly all professional cutters fracture test using several techniques, so opal is cut along cleavages to make clean stones
Some rough opal buyers have different techniques to fracture test the rough but it ranges from exposing rough out at night to hot and cold water or air pressure
Some cutters have tried vacuum pressure to check if any fractures in the rough opal
So today air travel is considered no problem for your Ethiopian opal but to be aware it is hydrophane opal