Strain-finally a scientific approach to the phenom.

[spicolicpa]

Taken quite a fixation on the Strain concept.

Here is a very well put together article that, while reminiscent of some jumbled IRS literature I have been forced to digest is very informative.

It does not finalize a conclusion on Strain in relation to cleavage but it does state that the propensity for cleavage using a semiemperical method (Combo of theory and practice) is greater in a diamond with planar weakness which occurred during dynamic growth (AKA the inclusions you see on your GIA report)....BUT that this does not entirely explain the domino effect (disintegration of molecular bond cohesion) that occurs when a diamond is cleaved, rather it is of secondary impact.

All things considered I would have liked to have known whether or not there was a high or low degree of strain in my stone. If in fact the cutter pays less for this type of rough, this price saving should be passed on to the purchaser as well.

At least the purchaser should have knowledge of this condition and make the choice?


Theoretical Strength and Clevage of a Diamond

 

[spicolicpa]

Taken from "ALLUVIAL EXPLORATION & MINING" website

Although the anomalous double refraction of diamond is, as rule, but feeble, stones exist in which it is comparatively strong, and which show much brighter polarization colors. This is the case in the "smoky stones" of South Africa, which, because of the great internal strain in their substance, have a tendency to fall to powder for no apparent reason. SPOOKY-but I am sure is not common is normal cases!

A parallel case is that of the drops of glass known as" Prince Rupert's drops," which also show strong double refraction as a consequence of internal strain.

There is never the slightest danger of confusing anomalous with true double refraction, for a mineral with true double refraction, such for example as quartz, colorless sapphire or topaz, will appear much more brilliantly illuminated when examined in the polarized light, and, moreover, will be uniformly light or uniformly dark over its whole surface.

Cool link to this article

 

[Garry H (Cut Nut)]

thanks Spic.

of the 2 articles, the more formal one is of most interest.
IUnfortunately it draws no conclusions on our area of interest. some of the findings:

Diamond strength is 7:2.8:1 i.e easiset to break in the octahedral plane, 2.8 times harder in the dodecahedra and 7 times harder to break in the cube direction. When broken in other than Oct - it is actually a series of oct step fractures.

Weakness is greater if growth defcts or dislocation or inclusions are in the octahedral plane.
More perfect cleavage if there are more dislocations and less inclusions.
"However there is no clear picture yet as to the role of impurities and defects on the room temperature fracture or failure of diamond." .".....cleavage behaviour can be explained without resorting to the influence of defects and thus the phenomenon is intrinsic to the diamond lattice. Of course this is not to say that defects will have no effect".

JURY IS STILL OUT

nOTHING HERE ABOUT STRAIN.

 

[skibum]

These are goods articles about strain in diamonds, but the question being raised in another thread regards the matter of putting undue stress/pressure on what is essentially a hard but brittle crystal. I believe tension settings are said to apply about 12,000psi to the diamond they are holding. That is alot of pressure. What do you engineers think of that? Are they really safe?

Cheers,
David

 

[Garry H (Cut Nut)]

In a perfect world diamond has by far the highest 'compressability' load capacity.
It is also the most (or up there) elastic material. (rubber bands are not elastic they do not return to their original shape after stretchng).

 

[niceice]

Strain may or may not be an issue with regards to the realistic lifetime durability of a diamond used for jewelry, however it's easy enough to check for and we do so as part of our evaluation process... It's going to be interesting to see how all of this plays out in terms of how it effects the industry if at all... We've noticed that certain suppliers seem to produce a lot of diamonds that have strain and others produce diamonds with little or no strain at all... Cheaper rough? Obviously we work more closely with the cutters who seem to have access to better rough without strain...

As far as the tension set mounting concept goes, it would be interesting to hear what somebody like Stephen Kretchmer has to say about strain since he is one of the designers that works with the tension settings... We know that he checks the diamonds out very carefully before setting them, but we don't know whether this is a consideration for him or not.

Thanks for the links to the articles, they'll make interesting reading during the quiet moments of the holiday season... Can you believe it's here already?

 

[spicolicpa]

I read somewhere that most tension settings put about 90 lbs of pressure on each side of the girdle...I wonder how this correlates to PSI?

In the womb....during diamond creation I am sure this is piddly in comparison....but then I think this pressure is a uniform sort..equal pressure on all sides.....but if pressure is exerted at a certain angle; in tandum with the "grain" I think it exposes an Achiles heal in the dimamond....ease of cleavage.

 

[RockDoc]

Great article... Thank for bringing it to the forum.

I agree that if a stone does have strain - particular if potentially hazardous either in wear or manufacturing, the price should be less.

At the wholesale level, stones are sold in parcels, so the pricing should be adjusted on the per carat price of the parcel dependent on the percentage of strained rough.

My only sort of dissenting opinion is that I have seen strain in MANY flawless diamonds about 25-30% .HOw does this relate to the information reported on gemological grading report?

I will grant you that many crystal inclusion and feathers have associated strain, but I am not sure about the difference for stones that show strain without associated inclusions.


Rockdoc

 

[spicolicpa]

I believe that what the article is stating is that cleavage is less likely in a "homopolar" solid like a non included diamond with low stress.

Put another way the worst case formula is:
High degree of inclusions (GIA report)+ High Degree of Strain + Dynamic Energy (Striking force at the right planar angle)= cleavage (Bye bye bling bling)

They do not finalize any exact conclusions on the likelihood of cleavage when strain is involved, but when "Unscientifically" correlated with the extreme case as noted above with the African Black diamonds with High stress that vaporize for no other reason than internal strain it does appear that strain has a place in the cleavage formula.

 

[Erik Carlson GG]

Here are a couple of pictures of a diamond with pretty severe twinning. Most diamond crystals with twinning have some degree of internal strain, however this diamond has it pretty bad. The first picture is of the diamond under normal lighting in the scope.

 

[Erik Carlson GG]

This second picture is the same view of the diamond under magnification except with crossed nicols.

enjoy...


Erik T. Carlson

 

[Richard Sherwood]

Nice photo, Erik. Thanks.