How To Dry Opals Safely

[PinkDiamond]

This article from the International Gem Society offers a way to dry opals 'safely', but I've never heard any of our cutters or miners say they did it this way. Has anyone used the baggie method?

How To Dry Opals Safely

Opals are very sensitive to sudden changes in temperature. If you purchase opals that have been stored in water, you’ll need to dry them slowly. “Rough Opal” by Deidre Wollard is licensed under CC By 2.0

"Question

I happened upon some opal in the raw when I was traveling in Honduras. There were ten pieces in a bottle filled with water. The man who sold them to me said I needed to keep them underwater. I’d like to have the opals shaped and polished for my wife as a present, but I’ve heard that they can crack if they dry out. I’ve also heard that silicone can be injected into opals for stability. Will that help?

Thanks,

Randy
Answer (Part 1)

Before you take your opals to a gem cutter or jewelry maker, you’ll have to dry them carefully and slowly. Opals do have significant water content (sometimes as high as 21%). If they dry too quickly they may indeed crack. That’s why sometimes they’re kept in water until they are sold. It relieves the merchant of the responsibility. (This is also a way to hide flaws. Buying opals kept in water is not recommended).

Take the opals out of the bottle but don’t dry them. Put them in a zip lock bag and then put that somewhere that isn’t too hot. Leave them there for six months to a year before having them cut.


“Precious Opal (Tablon Mine, near Erandique, southeastern Lempira Department, western Honduras) 1” by James St. John is licensed under CC By 2.0

When you store your finished opals, keep them away from sources of heat or cold and store them in soft, moist cotton. It’s not necessary to store them in water, oil, or glycerin. Your opals will be fine as long as you don’t subject them to sudden changes in temperature or rough handling. You can consult our opal care guide for more information.

Donald Clark, CSM IMG
Answer (Part 2) ... "
https://www.gemsociety.org/article/how- ... ls-safely/

[SwordfishMining]

Lots of people know about that method from here as stability is wanted not guaranteed. They bigger they are the more pieces when dry. I'm sure the method started with Mexican opals too as the supply was impacted by what would dry as mined to be cut and not craze unless it was sold as mined - damp or wet. If it was already dry and uncrazed, nobody puts that back in water after washing. Plastic baggies can differ in how fast they let water out so its not always 6 months and results will vary. I am guilty of shock drying most of what I find after putting it in water as mined, keeping wet what is valuable as a specimen of black opal fossils replaced wood or patterns and the rest gets put in a non airtight plastic jar or baggie usually for years before being reopened, sorted for brightness etc into other non airtight jugs for sale at the different price leves or used due to demand and everything else goes onto a cookie sheet to dry out totally. Yeah a bunch still comes out crazed but they say less does. AND you have to rewet it to cut it or it is not proven that it will not crack when it reabsorbs water or later redrying fast out of a baggie. Later I re-search all of that for stable common opal, cute woods and hydrophane that colored up when it dried. Hint. Contra Luz seldom gets real play of color as it dries and it is very crazy compared to precious even, so it's best kept wet. Once the pesky glue hating water is gone and the extent of opalization can be determined, dry "fire" evaluated, stability tested, It can be cut as a solid natural, sealed with a fracture sealer or vacumned with resin or backed whatever for production. I have heard many many ways to stabilize our sometimes stable material, but none that stabilize ALL "the material". Oiling was about the only way known to prolong drying until way after sale, that and the keep it in glycerin advice that came from you know where, and it was not the Americas as we dont even produce enough to talk about. Science= You have to chose your low density (LDPE) polypropylene for its water permeability characteristics to match your surroundings. It also comes in screw top jars. Claims for sale in Virgin Valley still before some lab figures out how to make every opal cuttable, then guess where the biggest blacks hide.
.

[mick]

I happened upon some opal in the raw when I was travelling in homduras.

There's ya problem.

Don't buy anything that is wet would be my advice.

As for Aussie opal some people think when you take it from the ground and stick it in the boot of a car it cracks
I've heard all sorts of nonsense.
A hundred million years is a long time in the ground.

Ice ages, desert, continental drift, mountains come and gone and oceans the same the opal lies there waiting for us.
All that was brittle has eroded away back into the silica atoms it formed from.

[SwordfishMining]

I was shocked the first time i dried a jar of wet Mexican rough. I thought rough from here changed different than everywhere else instead of just like other opal districts that have to be cured and proven prior to slabbing and cabbing. Wish i had so much i could put it in a cement mixer and just sort what survived. No cracky opal not locked in matrix is un ground after being turned with those shin crackers. I bet the tailings run there sparkles like glitter.

[mick]

That makes sense, has to be some good stuff in there somewhere. They way Opal forms, you just have to find the good pocket, then in commercial quantities.

[Shea_O]

Could someone remind me why using oil to dry opal is seen as a bad thing? It seems that oil driven desiccation is somehow lumped into the category of “treatment”, but my experience in biochemistry is telling me that’s not always true. Using oil to expel water from the silica matrix might be considered “treatment” in the context of having impure oil which has hydrocarbon chains of varying length, of which some could penetrate the silica matrix in an uncontrolled manner...such an oil, mineral oil, has been mentioned in the past as an option for drying a stone but it’s impure. There are oils (talking a pure oil now, like one mole of hexane) with hydrocarbon chains sufficiently long to be unable to penetrate the silica matrix. My thinking is that this kind of pure oil shouldn’t be considered “treatment” if there is no changing of the molecular structure of the silica matrix..and especially so if the oil is too long a hydrocarbon to penetrate the stone.


Opal is SiO2-n(H2O) and stacks in the form of layers of beads....and having too much excess water amongst the beads can cause cracking (bond breaking) during too fast of desiccation. My understanding is that a saturated hydrocarbon of sufficient length to not fit between the silica beads - but also repel excess water at the surface of the silica bead layer can cause diffusion of water from deeper in the silica sphere matrix to the surface. I’m wondering if Hexane for example is sufficient to accomplish this...but really I’m more curious about whether the water-needy silica at the surface would draw up water from deeper silica layers....causing a cascading effect of “drying” an opal from the inside out....If the water diffusing out of the stone were to be continually mixed with the oil it would reduce the desiccation rate as well.

Since Aussy opal is considered ideal for cutting/stability at ~7% water weight by mass, and VV opal is double or more this amount, then at a slow and controlled desiccation rate, we should be able to accomplish diffusion of the excess water (represented by an arbitrary amount “n” in the SiO2-n(H2O) formula) from deep in the stone to the surface of the stone as the hydrophobic oil repels what excess water is being “held” by the silica beads at the surface. Do this long enough and you should be able to reduce the overall water weight by mass of the opal.

Additionally, hexane is extremely close to water’s refractive index, so if it did penetrate the surface of the silica matrix a little bit, it shouldn’t interfere with the light diffraction too much. Water =1.33 and Hexane =1.37

https://refractiveindex.info/?shelf=org ... page=Kozma

Does anybody else have a background in chemistry/physics to bounce ideas?

[rocks2dust]

Could someone remind me why using oil to dry opal is seen as a bad thing? It seems that oil driven desiccation is somehow lumped into the category of “treatment”, but my experience in biochemistry is telling me that’s not always true. Using oil to expel water from the silica matrix might be considered “treatment” in the context of having impure oil which has hydrocarbon chains of varying length, of which some could penetrate the silica matrix in an uncontrolled manner...such an oil, mineral oil, has been mentioned in the past as an option for drying a stone but it’s impure. There are oils (talking a pure oil now, like one mole of hexane) with hydrocarbon chains sufficiently long to be unable to penetrate the silica matrix. My thinking is that this kind of pure oil shouldn’t be considered “treatment” if there is no changing of the molecular structure of the silica matrix..and especially so if the oil is too long a hydrocarbon to penetrate the stone.

Opal is SiO2-n(H2O) and stacks in the form of layers of beads....and having too much excess water amongst the beads can cause cracking (bond breaking) during too fast of desiccation. My understanding is that a saturated hydrocarbon of sufficient length to not fit between the silica beads - but also repel excess water at the surface of the silica bead layer can cause diffusion of water from deeper in the silica sphere matrix to the surface. I’m wondering if Hexane for example is sufficient to accomplish this...but really I’m more curious about whether the water-needy silica at the surface would draw up water from deeper silica layers....causing a cascading effect of “drying” an opal from the inside out....If the water diffusing out of the stone were to be continually mixed with the oil it would reduce the desiccation rate as well.

Since Aussy opal is considered ideal for cutting/stability at ~7% water weight by mass, and VV opal is double or more this amount, then at a slow and controlled desiccation rate, we should be able to accomplish diffusion of the excess water (represented by an arbitrary amount “n” in the SiO2-n(H2O) formula) from deep in the stone to the surface of the stone as the hydrophobic oil repels what excess water is being “held” by the silica beads at the surface. Do this long enough and you should be able to reduce the overall water weight by mass of the opal.

Additionally, hexane is extremely close to water’s refractive index, so if it did penetrate the surface of the silica matrix a little bit, it shouldn’t interfere with the light diffraction too much. Water =1.33 and Hexane =1.37

Just my thoughts: Oil (of any type) that does get into pores or cracks will eventually discolor in real-world UV conditions, and possibly even cloud the gem. Even treatments containing UV-resistant stabilizers will break down/alter over time. Oil does not stop crazing, which will resume once the piece is re-exposed to air (e.g., through wiping or wearing off of the oil layer). Oil impedes, rather than slows or stops, the drying process, and if it is going to crack it will crack. Even worse, as oil is rubbed off only part of the stone, resumed drying can be uneven, worsening any crazing. So, the advice is to avoid oil, glycerine and similar clarity enhancements. Hexane would evaporate even faster than water, so I don't see the benefit (plus I don't want an opal that smells like hexane).

It isn't excess water that causes cracking (except in some cases where the stone has dried out, been rehydrated and then exposed to something like heat). Rather, it is more often the case that water loss exposes and exacerbates fissures/layering already present in the stone. Opal forms in a process involving water that produces layers of the ordered spheres. Often/usually this involved repeated episodes of drying alternated with water-borne deposition. In that process, the weak points form within the layers, along interruption zones (such as can be formed during replacement of shell or wood) and/or as cracks that transect layers (like cracks in mud in a pond that dries repeatedly). Rapid heating (including when cutting a stone) can cause the water content to expand and open or worsen a pre-existing weak point, but it isn't really excess water, and the fissure or weak zone is already there in the structure. The "let it crack if it's going to crack" advice for material that is aimed at cutting gems seems the most sensible to me.

Gemologically, it is out-of-bounds to represent something that is artificially treated as untreated. A drying process doesn't equate to a treatment that is used to enhance color or clarity, but if a stone is being artificially clarity enhanced then the treatment must be disclosed. Even in the case of oil used emeralds to disguise surface-reaching cracks/fissures, the treatment must be disclosed (even though oiling emeralds is considered an "acceptable" treatment). An unoiled emerald VS2 emerald is going to fetch a higher price than an oiled VS2 stone, thus the need for disclosure.

[SwordfishMining]

A note on internal atomic structure differences between opals from different locations. Electron microscopy has show different refraction/ images of opal. The so called volcanic opal in younger rocks has little rays coming out signifying MOST specimens have partial crystallization in the silicon ionic structure, not just ordered rows of atoms lined up in apparent ring structure flattened out. The sedimentary, buried for 200million + longer, opal may be squished into minimum area into maximum density by atomic structure packing over time of a gel under pressure and ground water washing over eons.

[Shea_O]

Could someone remind me why using oil to dry opal is seen as a bad thing? It seems that oil driven desiccation is somehow lumped into the category of “treatment”, but my experience in biochemistry is telling me that’s not always true. Using oil to expel water from the silica matrix might be considered “treatment” in the context of having impure oil which has hydrocarbon chains of varying length, of which some could penetrate the silica matrix in an uncontrolled manner...such an oil, mineral oil, has been mentioned in the past as an option for drying a stone but it’s impure. There are oils (talking a pure oil now, like one mole of hexane) with hydrocarbon chains sufficiently long to be unable to penetrate the silica matrix. My thinking is that this kind of pure oil shouldn’t be considered “treatment” if there is no changing of the molecular structure of the silica matrix..and especially so if the oil is too long a hydrocarbon to penetrate the stone.

Opal is SiO2-n(H2O) and stacks in the form of layers of beads....and having too much excess water amongst the beads can cause cracking (bond breaking) during too fast of desiccation. My understanding is that a saturated hydrocarbon of sufficient length to not fit between the silica beads - but also repel excess water at the surface of the silica bead layer can cause diffusion of water from deeper in the silica sphere matrix to the surface. I’m wondering if Hexane for example is sufficient to accomplish this...but really I’m more curious about whether the water-needy silica at the surface would draw up water from deeper silica layers....causing a cascading effect of “drying” an opal from the inside out....If the water diffusing out of the stone were to be continually mixed with the oil it would reduce the desiccation rate as well.

Since Aussy opal is considered ideal for cutting/stability at ~7% water weight by mass, and VV opal is double or more this amount, then at a slow and controlled desiccation rate, we should be able to accomplish diffusion of the excess water (represented by an arbitrary amount “n” in the SiO2-n(H2O) formula) from deep in the stone to the surface of the stone as the hydrophobic oil repels what excess water is being “held” by the silica beads at the surface. Do this long enough and you should be able to reduce the overall water weight by mass of the opal.

Additionally, hexane is extremely close to water’s refractive index, so if it did penetrate the surface of the silica matrix a little bit, it shouldn’t interfere with the light diffraction too much. Water =1.33 and Hexane =1.37

Just my thoughts: Oil (of any type) that does get into pores or cracks will eventually discolor in real-world UV conditions, and possibly even cloud the gem. Even treatments containing UV-resistant stabilizers will break down/alter over time. Oil does not stop crazing, which will resume once the piece is re-exposed to air (e.g., through wiping or wearing off of the oil layer). Oil impedes, rather than slows or stops, the drying process, and if it is going to crack it will crack. Even worse, as oil is rubbed off only part of the stone, resumed drying can be uneven, worsening any crazing. So, the advice is to avoid oil, glycerine and similar clarity enhancements. Hexane would evaporate even faster than water, so I don't see the benefit (plus I don't want an opal that smells like hexane).

It isn't excess water that causes cracking (except in some cases where the stone has dried out, been rehydrated and then exposed to something like heat). Rather, it is more often the case that water loss exposes and exacerbates fissures/layering already present in the stone. Opal forms in a process involving water that produces layers of the ordered spheres. Often/usually this involved repeated episodes of drying alternated with water-borne deposition. In that process, the weak points form within the layers, along interruption zones (such as can be formed during replacement of shell or wood) and/or as cracks that transect layers (like cracks in mud in a pond that dries repeatedly). Rapid heating (including when cutting a stone) can cause the water content to expand and open or worsen a pre-existing weak point, but it isn't really excess water, and the fissure or weak zone is already there in the structure. The "let it crack if it's going to crack" advice for material that is aimed at cutting gems seems the most sensible to me.

Gemologically, it is out-of-bounds to represent something that is artificially treated as untreated. A drying process doesn't equate to a treatment that is used to enhance color or clarity, but if a stone is being artificially clarity enhanced then the treatment must be disclosed. Even in the case of oil used emeralds to disguise surface-reaching cracks/fissures, the treatment must be disclosed (even though oiling emeralds is considered an "acceptable" treatment). An unoiled emerald VS2 emerald is going to fetch a higher price than an oiled VS2 stone, thus the need for disclosure.

Yes Hexane is not the best example here to cover all the concepts. I started writing this last night far too late for a work night and lost the whole post! When I hit submit I was rerouted to the login screen! Haha. So this morning I scrambled the post together during a break, riding off the principles I thought of last night. Yes this was a rushed post and yes an opal that smells like hexane wouldn't be attractive!

I hope I didn't pose the thoughts in a way that suggested the excess water in opal is the cause of crazing, but rather the action of the water's evaporation.. under certain circumstances.

So now the question remains whether it's possible to generate an environment for opal to dehydrate without free hydrogens (open air drying) - at a "safe" and controllable rate. I suggested the oil environment to accomplish this and to also provide hydrophobic interaction at the surface of the silica matrix. I'd like to discuss if it's possible for an alternative to oil for generating water-needy SiO2 at the surface of the matrix that would draw up water from deeper layers due to electronegativity..or maybe even osmosis?....causing the migration of deep water to the surface and therefore “drying” the opal from the inside out.. Let's discuss how to accomplish this. I certainly believe this can be accomplished...the answer is out there... maybe in the form of a mild salt...maybe through osmosis a solution could be generated that reaches a state of equilibrium of water content such that the opal's water content decreases...

or....

Imagine placing an opal in an environment such as a complete vacuum -- no oxygen, hydrogen or any gases to interact with at all. The Silicon dioxide bonds wouldn't have any free gases to share their electrons with and therefore the two oxygen would remain bound to the tetravalent Silicon via double bonds. The water content embedded in the silicon dioxide matrix would also not necessarily be drawn to the surface (aka drawn out of the stone) due to any kind chemical reaction.....but rather compelled by the electronegativity of SiO2 through a deficit of hydrogen rich water at the surface..this surrounding water may interact slightly with inclusions within the opal, but there would now be an opportunity to take advantage of the electronically neutral and unreactive SiO2. We ultimately want the water lodged in as inert a substance as possible. We accomplish this via the vacuum.

Now we need to introduce something that will snatch up the water molecules off of the surface of the stone and result in a phase transition called deposition. This is when a gas transforms into a solid without ever becoming a liquid. Most importantly, the byproduct needs to also be chemically inert with respect to SiO2 (and hopefully any inclusions). Incrementally introduce minute amounts of said gas such that the entire quantity has reacted with water on the surface of the opal and is consumed. You will now have generated a water deficit at the surface of the stone which would draw out more water from within..... repeat?

[SwordfishMining]

The Australian Mineralogist magazine had an article on the chemistry for drying cracky Ethiopian opal in a bomb and also about how to cure hydrophane, I think it was March 2013