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How does color treating "work"?
  
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Tom Mazanec




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PostPosted: Apr 24, 2021 06:25    Post subject: How does color treating "work"?  

I read you can change colors of gems by dyeing, heat or radiation. Dyeing I can understand, but how does heat or radiation change a stone's color? The heat cools off and the radiation dies out, and neither should change the chemical composition of the mineral.
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PostPosted: Apr 24, 2021 06:38    Post subject: Re: How does color treating "work"?  

Light can also change their color, sometimes for the better and sometimes not. I have collected Baryte that goes blue after a time in sunlight and does not change back. That said a different pocket in the same mine will react differently.

I am sure we can find another thread that will have discussed this at length
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Amir Akhavan




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PostPosted: Apr 24, 2021 07:14    Post subject: Re: How does color treating "work"?  

>> and neither should change the chemical composition of the mineral.

Oh yes, it does.
It does not change the bulk composition of the material, that is, when you powderize and analyze the amount of different elements in it, you will not find a difference.
But there will be changes in its chemistry, either by moving electrons between different atoms, which, for example, changes their oxidation state, or by actually causing atoms to change places in the crystal structure (that's what often happens when you heat material).
The details are different for each treated substance and each method, and there are books written about it, so there's no short answer to that question and the physics and chemistry behind it is rather complicated.

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Peter Lemkin




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PostPosted: Apr 24, 2021 07:25    Post subject: Re: How does color treating "work"?  

Heat and radiation play a BIG role in some minerals as to what color they are when you find them [natural heating during formation and long after; ditto radiation - internal or external]. It doesn't change the GROSS chemical composition, but it can effect the micro chemical composition or the crystal lattice on the micro scale, or the chromphores, or crystal empty holes. Oxidation states can be altered. Some multicolored XX are due to changes in the temperature when different parts crystalllized. Some XX exposed to high or long-term radiation have completely [!] lost their crystal structure! This happens often in radioactive species or those that form near radioactive species. A XX is more complex than chemical composition. Color change is more complex than the outline, above....and the color changes are by more than one mechanism. Radiation can also be used to change color on some species. These changes are at the atomic level when atoms are hit by a photon of light or from radiation. As mentioned above, whole books are devoted to this.
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Riccardo Modanesi




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PostPosted: Apr 24, 2021 10:32    Post subject: Re: How does color treating "work"?  

Hi to everybody!
There is a lot of literature concerning gemstone treatments, like diamonds. quartzes. topazes. corundums, beryls etc. A typical case is their so- called "Maxixe-beryl, which loses its colour just by lighting, or "citrine" quartzes which are by almost 90% heated amethyst, or intense blue topazes which are irradiated by their biggest majority.
Greetings from Italy by Riccardo.

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Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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SteveB




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PostPosted: Apr 24, 2021 15:10    Post subject: Re: How does color treating "work"?  

Its very similar to “climate change”in that energy is put into a system causing rapid “unnatural” change. With minerals the energy comes from a radiation or heat source, usually in a pressure oven and this mimics the earths natural environment deep underground where minerals are formed.

Adding salt to a cup of water and letting it sit will let you grow sodium chloride crystals because the atoms under room temperature/pressure conditions obey the laws of physics and chemistry to form chemical bonds in a particular way and in this instance the stable formation is also a repeatable one to form a lattice and eventually a crystal. Atoms bond with other atoms in preferred stable configurations under specific conditions. You’ve seen those models of chemicals using balls and sticks? These fairly accurately represent how atoms fit together to form molecules. The angles of how the atoms are joined together are vital to known not just the atoms themselves. At higher pressures and temperatures the atoms may form a different configuration comfortably, once the heat /pressure is removed the atoms are under stress in an unnatural shape and may break rapidly because the energy of the system no longer is enough to maintain that configuration.

It may be the original minerals specimen already has atomic stresses from for example being ejected into the sea from a volcanic eruption where the heat and pressure energy is vastly different from what the formation was relaxing with.

The molecular shapes formed tend to determine opacity and shape mostly, not sure if colour is mostly molecular or atomic. Trace elements are contaminants in the liquid soup of atoms from which minerals form. The soup is never idilic and pure there are always some trace elements present and depending on the heat and pressure present these may prefer certain molecular bonds contrary to the majority of the soup so as heat/pressure (ie energy) changes you can get several stable molecules forming and possibly competing for space. Its where inclusions can come from as certain unwanted trace elements find each other to form their own stable crystalline growth .

By applying energy (heat and energy) to an existing specimen it can force stressed or broken molecular bonds to reform in a more relaxed and stable configuration. Usually towards clarity of the specimen. It can also allow some trace elements to be drawn out completelyor extra trace elements added to enhance/alter the colour. Often the pressure oven doesnt rely on air inside it, instead vaporised gas rich in a particular element are pumped into the sealed “oven”. The element may be there to bond with impurities to draw them out or maybe encourage new bonds and formation. This is the dyeing and/or coating processes typically.

The molecular shapes formed take place at certain temperatures and pressures for different minerals. So it requires precise control ovens to get to the desired range to encourage the molecular bonding you want for the result you want. Its not just as simple as dumping a bunch of rocks in your home oven and cooking them for an hour at the hotest setting. Though it will be a non-room temperature energy combination it can effect some minerals but not neccessarily in how you will want. You have to clean your home ovens as particles from foods change fromsolid or liquid state to a gaseous state and are deposited on the inside surfaces and reform into unwanted culinary “slag”. Next time you cook some of this slag becomes gaseous and can mix into your food being cooked noticable by a tainted taste. Likewise if you try to roast your rocks there’s no knowing what poisonous molecules can contaminate your home oven and released into the air in your kitchen. Just not something to play around with in your home. There are furnace ovens you can buy and use them outside if you want to experiment.

I’ve repeated temperature/pressure/energy a number of times. Its all energy of course and it comes in different forms and its not as simple as saying 1+1 = 2. The earth gets energy from the sun primarily as light of the electromagetic spectra which hits the surface of the planet some is absorbed and some reflected depending on what it encounters. So local air everywhere on the planet is effected to differing amounts so the way it moves and reacts differs from place to place. Magnetism which you get from electricity mostly is another form and often heat is a waste byproduct of energy being used. Energy can’t be created or destroyed only transformed. So the more we use as a species the more waste energy is produced and doesnt go nowhere, its used in an infinite number of ways by other organisms and physical processes we are all trapped in this single room called the earth together with.

Through trial and error centuries ago people found some minerals could be colour changed by heating in their camp fires. Metals from rocks likewise discover this way. By observing and trying bigger/smaller fires and rocks variations in the physical changes could be noted which the conditions required to reproduce them. As science and technology progressed we developed ways to better test the conditions and predict the results more accurately. Today its still no absolute to know what will happen to this mineral specimen I hold in my hand if I do X to it. The point of modifying of course is to profit, either by making a specimen appear a better form of the mineral or to alter a worthless common mineral such that it appears to be a different mineral altogether. Its a method of fraud trying to mask the appearance of a thing as another thing. Paint is easily scraped away to reveal a deception. Heating/irriadation can’t be easily washed off. Accurate hardness and density measurements are the best way for most people to know a mineral is what its being claimed to be. It is possible tu turn lead into gold but the energy required is so massive its just not economically viable to do and I’ve only heard of it being done with particle accelerators. But chucking a handful of boring (Worthless) gravel spinels into a furnace oven might change some enough for dodgy people to sell to unsuspecting buyers as ruby or sapphires. Profit. And energy.

And its almost impossible to test if a specimen has been treated in some form, hardness and specific gravity testing before you buy will help confirm its what its claimed to be. Also some minerals like sapphires are heat treated by default at many mines because the colour and clarity is largely what drives the prices plus they are often destined to be gem cut and heating has no negative effect to that that can’t be seen before cutting. While many may not see artificial enhancement as a problem since typically people care about what it looks like not the honesty of it. The fact that treatment often can’t be determined by any means it means every time a specimen changes ownership the honest information of it is increasingly lost or embellished for financial gains. The honestly is quickly lost which says much about the human race as a species.

One last point if you are thinking this is a great DIY get rich hobby for you. Firstly the equipment required is expensive and its not like a video game where some specimens might get “improved” leaving the rest unaltered. Thats not true. Without the knowledge and skills to first use the correct equipment (any old oven is nothing like the correct types to be used in enhancement nor is operating them the same as baking a cake). Adding energy in any form can have unpredictable results. Most people know many things expand slightly when heated and shrink when cooled, so any microscopic fractures present in a sample could mean when heated the specimen might shatter apart leaving you wil nothing but worthless shards. Might as well have just hit them with a hammer, its cheaper. It can also mean workIng with hazardous chemicals and/or possibly releasing them from a specimen that you might inhale. Such as mercury or arsenic or lead plus there are so many radioactive elements and compounds which occur naturally at low levels but releasing them into a gaseous state allows them to get into your eyes, mouth and lungs very efficiently in far more concentrated amounts. I’m sure if you’d search around you can find places to take mineral specimens for enhancement if you want Just like a quick google search would have answered the original posters question.
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Roger Warin




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PostPosted: Apr 24, 2021 16:19    Post subject: Re: How does color treating "work"?  

Hello,

Being a chemist, and president of an amateur club AGAB (Belgium), I saw fit to specify the "real" origin of the colors of ruby and sapphire. So I published 2 articles on this subject for my aficionados.

These are two articles focused on corundum, the mineral species of these two gems. Sapphire and ruby are varieties of corundum.
The problem is complex because there may be red sapphires (but not the red of the ruby !).
The origin of the color of a gem is difficult to understand for the amateur not initiated in physicochemistry (it is moreover for this reason that I became a chemist more than 65 years ago!).
I offer 2 pdf's in French if you wish it personally.
Your artificial intelligence will still be able to translate.
A article of 17 pages for the sapphire and 14 pages for the ruby.
For Sapphire :
1) the blue color of sapphire is mainly due to charge transfers between different valence states of different cations, impurities of the crystal:
2) Fe2+ and Ti4+ → Fe3+ + Ti3+.

For ruby, the first reflex of the gemologist is astonishment, because Cr3+ rather induces a green tint (of idiomorphic origin) as in chromium sulphate. In the case of ruby, under the incidence of light radiation, a charge transfer occurs between an O2- anion and the Cr3+ cation.

I'm sorry, but this is "Chinese" to many. It is for this reason that these questions about the origin of colors are recurrent.
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