Gemstone Treatment and Enhancement

Any process other than cutting and polishing that improves the appearance color, clarity, phenomena or durability called enhancement.
Beauty enhancing treatments can produce remarkable results. Less expensive materials can be transformed into beautiful
gemstones.

Heating gemstones under controlled conditions rearranges the atoms in the gemstone which removes or improves the colour. Tourmalines are frequently heated to lighten the color. Blue zircons are usually heated and the resulting color is permanent. Since heating is generally permanent, heated stones do not require special care.

Bleaching, coating, dyeing, filling, impregnation and waxing methods are used for Semi permanent or temporary gem enhancement, However flux healing, fracture filling, heat treatment, irradiation, lattice diffusion and
lasering can make permanent effects on gemstones.

Oiling process used to enhance the clarity of Ruby, sapphire , Tourmaline and emeralds. Oil is applied to the stone by pressure plus vacuum to enhance its clarity through different lubricating machines and these machine can be used at home, in the office or anywhere because of it’s simplicity way of use.

For some stones treatment or enhancement can reduce its value? For example, a large, untreated, (color unchanged) stone is much more desirable on the marketplace than a similarly “treated” stone and will never lose its color or beauty.

There is nothing intrinsically wrong with gem enhancements as long as you are made aware of their use.



Edited 1 time(s). Last edit at 04/02/2009 06:09PM by Uwe Kolitsch.

Hammad,
You said:
Heating gemstones under controlled conditions rearranges the atoms in the gemstone which removes or improves the colour.

It is my understand that heat treatment of gemstones does not rearrange the atoms in a gemstone. What is the basis of your claim that is does?

Rock Currier
Crystals not pistols.

Dear Rock Currier

If you do a little research you will find out that heating does rearrange the atoms in the gemstone. You can see two links below and i hope there are alot on the web. Thanks for asking.

Regards

Hammad


( What does this treatment do to the stone?: Basically, it rearranges the atoms in the gemstone. Sometimes, as in the case of ruby, the stone is heated almost to a point of melting, which lets the aluminum oxide in the stone reform to what is basically a new crystal structure. This lets the chromium reform to give off a better color of red. The same can apply to a type of sapphire known as gouda sapphires. These are milky white sapphires that turn blue, and account for many of the promotional quality sapphires out on the market today. Heat Treatment)



( Heating only rearranges the atoms, it does not add or subtract atoms. Some yellow, golden, and orange sapphires are irradiated. This is not acceptable. The simple way to detect this is what is called a fade test. Simply place your stone in the sun for a few days. If it fades, it is irradiated. )Under - Heating

"which lets the aluminum oxide in the stone reform to what is basically a new crystal structure"
That's incorrect. There is some diffusion and the average Al-O and Cr-O bond distances might change slightly. The crystal structure stays the same, however.

Uwe , doesn't the excitation of atoms, during heating of star sapphires in particular, open up the lattice a bit and allow the rutile to redistribute and recrystallize more evenly giving a better star,and in that way alter somewhat, the pre-existing crystal structure...????

Hammad,
I'm curious. Are you involved in selling gems to the new age movement?

Thank you for the two links you provided in your email. Is it the information contained in those two articles that make you think the atoms in heat treated gems are rearranged? Could you be a bit more specific about how the atoms in gems are rearranged by heating? Perhaps you could give us an example of a particular gemstone where the atoms are rearranged and how they are rearranged.

Rock Currier
Crystals not pistols.

Hi there,

They are ( International School of Gemology) a quite well known organization. If they or my understanding is wrong then i am with you for sure.


Heat Treatment

( ...What does this treatment do to the stone?: ....... [b Basically, it rearranges the atoms in the gemstone.[/b] Sometimes, as in the case of ruby, the stone is heated almost to a point of melting, which lets the aluminum oxide in the stone reform to what is basically a new crystal structure. This lets the chromium reform to give off a better color of red. The same can apply to a type of sapphire known as gouda sapphires. These are milky white sapphires that turn blue, and account for many of the promotional quality sapphires out on the market today ).

I think the exact mechanism of the color change by heating depends on exactly what is being heated, how it's being heated (and cooled), how hot it's being heated to, how long it's held at that temperature, and what environment it's being heated in.

I'm sure there are those who here who know far more about the specifics of the subject than I do, but as far as I know, a hydrate may change color when heated due to the loss of water molcules, and some things change color due to a change in the number of valence electrons of an ion in the impurities (via redox?). I think most heat treatments act on the impurities, though I imagine there are cases when the heating causes a deformation of the crystal lattice of the pure mineral...or an undoing of a deformation.

It's all fiddling with the crystal lattice in one way or another :-)

Heating can allow the diffusion of chromophore elements applies the surface of a stone into its interior, but this sort of treatment usually only effects a surface layer on the stone because of the difficulty in getting ions to travel great distances in a solid state. It is my understanding that heat treatment of gemstones is usually done to change the oxidation state of multi-valence chromophore elements such as iron. Heat it in an oxidizing environment and iron will change from +2 to +3 valence, which is what happens when low grade amethyst is "cooked" to make citrine. Heating in a reducing environment will cause the reverse reaction and is used to lighten up dark blue sapphires and sometimes lighten dark tourmalines. Diffusion of chromophore elements might qualify as "rearranging atoms" within a gemstone, but I don't think changing the oxidation state of those already present does.

"Uwe , doesn't the excitation of atoms, during heating of star sapphires in particular, open up the lattice a bit and allow the rutile to redistribute and recrystallize more evenly giving a better star,and in that way alter somewhat, the pre-existing crystal structure...????"

Ray: the crystal structure is defined by the space-group symmetry and the overall atomic arrangement.
What you probably allude to is that rutile can exsolve from and dissolve in the corundum structure, depending on heat treatment and bulk Ti content. Then you're talking about two different crystal structures which are intergrown in an oriented way. If they are present, they don't change during the heat treatment.

[www.agta-gtc.org]
[seismo.berkeley.edu]

Also, blue zircons are not heated to make them permanent. Zircons are heated to make them turn blue and be that color permanently.

Also, not all heat treated gemstones are permanent and some do require special care.

Fracture filling is also not necessarily permanent either. If the method of filling is via epoxy, resins, or glass it will last a long time with proper care, but not permanently as eventually the materials used for filling will break down.

Treatments almost always decrease the value of a gemstone! Some treatments far more then others. Heat for example decreases value only slightly in most stones, but diffusion tends to have a very negative impact on value except for Be Diffusion/Heating on sapphires/rubies which has now become widely accepted due to its permanence and has steadily been increasing in value ever since. Some gemstones require treatments in order for them to exist.... praisiolite, Honduran Black Opal, Andamooka opals, much turquoise produced today, etc. Without treatments these stones would either not exist or not be viable as gemstones, but only samples.

No, there is nothing at all wrong with treatments as long as they are fully disclosed and cost reflects the exiting treatments. Treatments make many gemstones affordable to those who would normally not be able to afford them.