Hydrophane Opal is a new term that has been developed to describe a certain type of Opal. Opals have been mined in Europe for thousands of years and in Australia for over 165 years. However the discovery ofEthiopian opals and Hydrophane opals has only been around for about 20 years. In the last 10 years there has been in increase in the commercial quantities of this material.
Louis Leakey, the well-known anthropologist, uncovered the first known opal relics in a cave located in Kenya. During the 4000 B.C they most possibly came from Ethiopia. Its interesting that the oldest opal known possibly came from Ethiopia which is now considered a new opal field.
I started buying small amounts of rough Welo in 2008 and increased to multiple kilos by now. I’ve cut a couple of thousand stones from Welo and worked on developing procedures that worked for me during 2008 and sold my first Welo in 2009. I’ve now sold hundreds of cured Welo Gems and keep a study group of cut Welo with many different types and patterns. All are Hydrophane.
Welo has 2 types of opal and as you’ve been reading, most is “Hydrophane”, soaks up large amounts of water and dries out large amounts of water. and “Non Hydrophane” which acts very similar to Australian Opal and cuts the same. Hydrophane is the Opal that also looses color and changes clarity when exposed to large amounts of water. I cut all of my Welo with a Genie Machine under a water flush and the total immersion for a couple of hours mostly turns the White Base Hydrophane opal crystal clear and sometimes washes all, or most, of the color away. Not to fret though even after hours of water and going through the most difficult upheaval of their existence, being cut and polished, almost all come through with “Flying Colors” and they all return to their previous appearance and all that color catches up andsome really “fly”!!!
When buying my rough Welo I buy 5 gram stones and above with 10g to 40g common. Better than the mine run rough that most arecutting from!! I use larger stones because I don’t dop my rough while cutting, just hold them in hand. One advantage of that is Welo won’t adjust to heat evenly and tends to fracture if exposed to much heat so if I dop I cold dop. That is just my preference, but it increases my yield which can be very low, in most cases there is about 2/3 loss in stones being cleaned of matrix and some natural fractures, to a finished gem. That can be increased by selecting each stone, but that is very difficult here in the US.
With Welo I find from experience that the rough must be cut to at least 3000 diamond grit (if you use diamond) to seal the surface so it expands and contracts in a uniform manner, if you cut part of the way and leave it dryfor an hour or two, it is likely to be fractured when you return. Also if you leave any matrix in it also reacts differently than the host opal and may cause cracking. I polish to a 14K grit and finalpolish with Cerium Oxide for a mirror finish. This highly polished finish tends to curb the loss or gain of water in amounts that occur when wearing the gemsand cuts down on the absorption of any foreign materials through its surface and diminishes the tendency to react to different climates. This is what seals the surface so you can get your Welo Gems quite wet without noticeable basecolor loss or loss of brilliance.
I also cut some Welo that is black on crystal base and find almost all is non-hydrophane. All Hyrophane Opal varies in the amount of hydrophane properties it possesses. It can vary from almost unnoticeable when we cut it to so hydrophane that it sticks to our fingers, if we have any moisture at all on them, kind of like the kid sticking his tongue to piece of playground equipment when it’s frozen and it freezes his tongue to it immediately!!
The yellow centers, or “Yolk” of Welo, some cutters automatically remove them, but I haven’t found a correlation between cracks and yolks so I remove them if they aren’t artistically appealing, but some have colorplay and sometimes are attractive, by the way some aren’t yellow at all,they can go to completely clear void of color.
I find that by completely sealing the surface by this system of polishing makes it unnecessary to use other sealers, but is is necessary to finish all the sides to seal it.
There are many “geometric” patterns, such as Honeycomb, Fishscale, Rainbow Prism, Ribbon and many others that you can see in Opal Auctions literature andby common usage have become accepted descriptions that are very rare in opal from most other localities, but found in Ethiopian opal and some are considered a premium and might auction at higher prices than other patterns.
Some gems cut withone pattern on one side and the other side is a completely different pattern. The patterns are usually determined by a cellular structure making up the gem and viewing these cells at different angles changes the Pattern that it produces.
Here is where most lapidaries will disagree with my method, but it works for me, and doesn’t affect the stability of the Rub. When you are looking to cut the rough into a gem, I will dip the rough once in water and study the reaction on the surface of the rough. If there are any fractures in the rough they will absorb water into the cracks and after just seconds darker lines start to appear where the cracks walls absorb the water and turn clear in a fine line where the cracks are. It will show any cracks if you are cutting it and you look close enough, and look carefully and it will give you an idea how deep the cracks go. Some cracks are just on the surface and can be ground or polished away, like crazing. Sometimes crazing can enhance the colorplay of the finished gem. If the finished gem makes it through the cutting and polishing after a day or so it will have done any cracking or crazing it is goung to do, so by the time you see it on Auction it has done what it is going to do if it has been throughly polished. I havent had anyFine Welo Gems crack in my study stones or had any returned from cracking. Be asured, with proper care, washing with soap and water when the are a little scrungy is about all they need. Not necessary to keep them in any liquids such as water or glycerine or oil, keep them out of laying in direct sun like you might have through a window or any heat source, if your hand can take the heat so will your Welo Hydrophane Opal!!
Since I mentioned crazing, it isn’t always detrimental. I have a 330ct Welo crystal with beautiful fire and color that is completely crazed throughout the surface and this crazing refracts the light such that it increases the color play. I’ve designed this huge Welo Crystal into a mushroom by attaching a welo base that gives it some depth and purpose and it looks just like a mushroom. I’ve polished through some windows to expose the fracture free insides of the gem and it also exposes another unique aberration of the welo and that is a “Phantom”!! This phenomena looks like an opal within an opal, some have colorplay, sometimes different than the host opal while others are just a light gray. This “phantom” is also being discussed by opinions from different camps as to what they are and how they form.
That brings me to Welo formations and we know that Welo, like Mexican and many othersare Volcanic in origin but I also have several with plant matter such as roots and straw and others that are definite “Limb Casts”, which lends creedence to the possibility of longer term seepage replacement with the twigs and roots appearing as fossils inside the opal.
For Hydrophane Welo the buying public want thesebeautiful colors andpatterns and they are out there for interested parties to discover, even in smaller rough, they can be found. You’ll see listings with a brilliance description such as 5 of 5 or 3.5 of 5 and that is referring to the dullest colors as 1 and the mostbrilliant as 5. Welo has some of the mostbrilliant crystal opals and varied patterns and colorplay of any if you are looking for those properties.
When we first started experimenting with Welo opal we realized that it is important to have a rest or drying time before they are brought to market and most agreed that we would try a year (12 months) of resting. After my studies of these gems I am of the opinion that a full year is not necesary so I usually rest my Hydrophane Opal for several months, or in some instances shorter, depending on the amount of Hydrophane Properties each gem portrays.
Now for “NON HYDROPHANE” Welo, just a line or two!! It consists of 10 to 20% of all Welo I’ve worked and it cuts and acts just like Australian in nearly ever manner.
Those are some of my thoughts and findings after working a few years and thousands of stones with the deceptive Welo Hydrophane!!
Does the depth of mining determine how stable Ethiopian opal is?
No research has been done on this factor if opal mined in certain areas as to how it was formed and does this effect the opals stability.
In the opal fields at lightning Ridge, the miners know if you go deep in some fields that the opal is not as stable.
Most miners work 20-30-meter depth and opals are stable, but if you go deep in some areas the potch is softer and the opals will not be as stable.
Some opal fields have reputation like Mehive that lot of opal is unstable and crystal is used to make doublets or triplets
The potch is also softer and more a wet clay appearance than a dry clay look.
But in Ethiopia the opal is volcanic and miner will work horizontal not vertical as most opal mines are.
As this Ethiopian opal was formed in violent volcanic areas with many earthquakes and the country has reputation of massive earthquakes and volcanic activity.
So, when new opal deposits are found it is impossible to see how it was formed and at what depths
This could be the reason why some areas have higher cracking problem than others and if you follow Ethiopian sellers feedback on opalauctions you will see lot repeat buyers buying , so this location where the opal came from is more stable.
Its not scientific but could explain why some parcels of Ethiopian rough produce more stable opals.
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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Non-Hydrophane are excellent to cut
Australian opals are non-hydrophane and very rare to have an Australian Hydrophane opal.
Australian Opal fields from Boulder to Lightning ridge and south Australia are all non- hydrophane opals
Small opal field of Tintenbar is reported to have some hydrophane opal but there is no commercial opal mining now in this area.
It is personal preference on what opal fields people like to cut and polish
Opal cutting a s hobby is on the increase and can be financially rewarding also.
To start, I suggest cutters buy some Ethiopian and boulder opal rough and when more experienced than buy Lightning Ridge rough material