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Q: Finding a treatment/method to increase the hardness of gemstones ( No Answer,   1 Comment )
Subject: Finding a treatment/method to increase the hardness of gemstones
Category: Science > Chemistry
Asked by: freakingcat-ga
List Price: $200.00
Posted: 07 Jun 2006 01:18 PDT
Expires: 07 Jul 2006 01:18 PDT
Question ID: 736006
I am working with a mineral called Sphalerite, ZnS, which has a
6-folded cleavage and a hardness of 3.5 to 4. When gemstones are
facetted out of this mineral they display a dispersion which is higher
than diamond. The problem I am trying to solve is connected with its
low hardness. When pressure is applied to the finished gemstone (like
when it is set), due to its low hardness and 6-folded cleavage it
usually chips on the edges. Further by exposing the facetted
sphalerite to bright light and by daily wear it becomes stained and
matt on the surface.

I am looking for a way to increase the hardness of this material
without changing its other physical properties. ZnS has a low
temperature resistance point so that when high temperatures are
applied, it dissolves into powder. Further its chemical structures
change (S).

I had been experimenting a lot and came to the conclusion that
probably the only way to increase the hardness without effecting the
other properties of sphalerites is a very thin coating.

Gemstones like pink topaz are already coated to apply a very thin
layer of color. My idea is to find a coating which can be industrially
applied which is colorless (thus not effecting the optical appearance
of the facetted sphalerites) BUT HARD ENOUGH to make it scratch and
wear resistable so that it can also be used for setting.

One researcher at Bangkok university acchieved a break through when he
used as he said a ceramic based coating (mixed out of two ready made
and available agents) but this information is not verified.

I am accepting as answer for this question the name and seller
information of a ready made coating agent which can be used and easily
applied on the gemstone which enhances its hardness while not
effecting other properties.

Further I accept as answer the confirmed contact information of
companies who are able to do this gemstone coating (hardening) for
customers in a reasonable price range.

It is also possible to accept information which show another way that
this hardening problem can be solved.

Further possible are verified contacts in Thailand (where I live at
the moment) who are able to do this kind of hardening treatment.

I have already invested quite a lot of time into finding a practical
solution to this problem and I am willing to offer not only $200 which
is the maximum amount I can select in Google, but $ 1000 for a
PRACTICAL applicable solution where the results can be verified.

thanks a lot!

Request for Question Clarification by pafalafa-ga on 09 Jun 2006 16:07 PDT
I have come across several references that mention the application of
a boron coating as an effective way of increasing the hardness of

However, all the materials I've seen thus far have been from
laboratories, rather than actual industrial applications, so I'm not
sure how readily the process could be applied to your gems.

Nor is there any assurance that what seems to work with diamonds would
also work with sphalerite.

Would you like to have the boron information anyway, as a starting point?  

Or would you only accept as an answer a process clearly demonstrated
to work on sphalerite in a commercial setting?

Let me know your thoughts.



Clarification of Question by freakingcat-ga on 11 Jun 2006 06:00 PDT
This difficult question can be declared solved when a practical
solution to increase the hardness for sphalerites (at least to a
hardness of 6, so that it can be used in settings) is found. I have
experimented a lot with this material and the main problem of
sphalerites (in opposition to other gems) is the low temperature point
(if it is heated for 2 hours above 150 degrees celsius it pulverized).
Various form of coatings have been tried out, the problem to make a
coating stick to the surface has been solved, but as the coating layer
has to be superthin so that the optical properties are not disturbed,
the hardness problem remained. I don't know how the qualities of the
boron coating. If it can be applied thin enough and sticks on the
surface, plus can be applied at low temperatures and increases the
hardness, it would definitely be a solution if it can be applied in a
simple way (commercial coating applications like used for topaz color
coating etc).

If you need samples for testing a coating (to submit it to a company
who does Boron coating) to see the effect, it can of course be

thanks for taking your time to answer this difficult question.

There is no answer at this time.

Subject: Re: Finding a treatment/method to increase the hardness of gemstones
From: redfoxjumps-ga on 08 Jun 2006 02:27 PDT
I know of firm that made a radiation device to increase the clarity
and value of gem stones.  Hardness?  Don't kno that.

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