Crazing and cracks

Where did you purchase the parcel from? I've never heard of putting them in mineral oil. Good cutting opal so far as I've experienced is sold dry. You want to avoid excessive heat, but that's true for all opal.

Hmm, just the opposite of my experience with Opals.  I have never, ever had an Aussie opal craze, but the Ethiopian/Welo does with frightening regularity.  Spencer does sometimes and Virgin Valley almost always unless it came from the Bonanza mine up on the ridge.

I just cut, mounted and sold a 19 carat (finished weight) full thickness, not doublet, Lightning Ridge that I have had stored dry for close to 15 years

Showing a prime example of a high end opal that started to craze over time. First shot was the finished opal before sitting for maybe 3 years. Second shot shows the crack that developed over time, I discovered later on. Third shot is what I got out of it after recutting the crack off. Guess what??? It did it again, and now its in my NG pile.

how sad this thread is. what lovely pieces gone to waste. I guess that is why it is precious, such fleeting beauty.

I'm no expert on Opals by any stretch. But I have cut several over the years, mostly Australian. Not only does location of the source seem to play a role in how stable opals are, but also how they are handled after they come out of the ground. Most precious opals have a high water content when they come out of the ground. Some miners slow dry their opals before selling to prove stability, while others put them straight into water rather than go through the drying process. Putting them straight into water bypasses any responsibility of first seeing how stable their material is before selling plus keeps the weight a little higher.

When I have bought rough opals I have kept this in mind. I will not pay as much for opal sold wet as I will for equivalent quality opal sold dry. When I have bought opals that have been stored in Jars of water I always slow dry them out before reselling or cutting. I place the wet opals in a small zip lock bag but do not seal it and then place the small unsealed zip lock bag with the opal in a larger sealed zip lock bag for several weeks. Some of the moisture will evaporate from the small bag of opal into the larger sealed zip lock where it is trapped so the opal doesn't dry out too fast. After a few weeks I unseal the larger zip lock and let the moister slowly evaporate from both. I've seen other people dry larger quantities like this using Rubbermaid or Tupperware containers. IMO taking wet opal straight from a jar of water and then cutting is asking for trouble.

As for dopping, in the early days I ruined my share by over heating. Not only can over heating crack opal but can also turn is chalky white. An alternative to conventional dopping I saw an old cutter use to avoid heat all together was to use Durham's Wood Putty powder mixed with water to adhere the stone to the dop. After the wood putty dries it can be coated with shellac to water proof it while cabbing. After cabbing the opal scrape the shellac off the wood putty with a x-acto knife and then soak it in water to dissolve the Durahm's Wood Putty. But I would think this process may rehydrate the opal and require slow drying it out again. I have not tried this process myself yet so can't personally verify how well it works.

As for storing rough opal in oil I have never heard of doing this and would never buy opal that was. Oil is too often used to hide defects in other gemstones and I would be highly skeptical of any oiled opal rough being offered. That said, back in the 70s I remember Jewelers used to tell their customers to rub their cabbed opal stone on the side of their nose once in a while believing that the body oil from their noses would keep the opal from cracking. I know this sounds weird but that was a common practice back then. I store my dry opal rough in air tight sealed jars or small sealed zip lock baggies.

As for storing already cabbed Opals, I've never had problems with small cabs being stored for long periods of time in paper sleeves or gem jars. But I did buy some very large cabbed Australian opals as part of an old collection that had probably been cabbed for twenty years before I bought them. I stored them in the same paper sleeves they were in when I bought them but after a couple of years they began cracking. I don't know if this was due to the atmosphere being drier where I am or if there was some other reason. Either way it's a sick feeling when it happens.

Larry C

This is cool to try if you have some lower grade Welo laying around. Drop some food coloring "your choice of color" into a glass of water and place your Welo in. Wait awhile then take it out. A lot of the Welo absorbs water so anything in the water is going to be absorbed also.
If you flush the stone afterwards a few times in clean water, it'll go back to norm.

My opinion; no oil. If a guy trying to sell me opal tells me they need to be stored in oil I would be highly suspicious that this variety of opal is very susceptible to cracking OR that the opal is already cracked and oil is being used to hide this fact. If the later was the case then cleaning the oil out would expose the cracks.

I keep most of my rough opal stored dry in air tight screw cap jars or in sealed zip lock bags. I do have a couple of jars of opal in water that I bought as part of old collections that I haven't done anything with yet. But before I do I will slow dry them out. If they are already stored in water then keeping them in it isn't likely to do them any harm. It's drying them out without drying them too quickly, or without getting them too dry that is tricky. Seems some opals are going to eventually crack regardless but we do what we can to prevent this.
Larry C.