Internal Graining gets missed a lot by GIA

[Garry H (Cut Nut)]

As a lover of blue fluorescent diamonds I feel not mentioning Internal graining makes it hard for good retailers and savvy consumers to avoid milky hazy fluorescent diamonds.
Simply, GIA miss most internally graining on their grading reports of diamonds.
Because they did their clarity grading with a backlit microscope, they would have naturally missed a lot of graining because the feild of view has little or no dispersion. It is much easier to see graining on the facet change in a video when a facet turns blue or grey from white or black.
A scientist friend explains it this way: "to be seen in a somewhat different "colour", ie wavelength, or intensity, thereby increasing the visual contrast between the grained & non-grained zones, & so emphasizing the visibility of the grain which would be otherwise minimally visible in overall diffused & non-dispersed white light.
This is much easier to see in videos of the stone rotating between pins (as opposed to normal 360 videos commonly used for consumers).
Given that GIA and IBM are digitising and automating AI clarity grading, I expect internal gaining will even more rarely be captured in their clarity grading in the future!

So for all you expert helpers here, please note that when surface graining is noted - there is almost always internal graining.
Here is an example in office type light and in microscope type light (thanks Cutwise!:

EX Round, 1.07ct, F, SI2, VG, EX, MED, +0.7%

EX Round, 1.07ct, F, SI2, VG, EX, MED, +0.7%

cutwise.com

EX Round, 1.07ct, F, SI2, VG, EX, MED, +0.7%

EX Round, 1.07ct, F, SI2, VG, EX, MED, +0.7%

cutwise.com

 

[Karl_K]

The 360 videos also have a lot of environmental color in them.
We know some like blue shirts, others brown shirts and some yellow, its rarer but pink/red has been observed
My guess, based on how often they show up its uniforms.
They need to wear white.

 

[Garry H (Cut Nut)]

From another scientist above my pay grade:
"Interesting observation. My take is the colour is there on account of the refractive index at a surface where there is a refraction. A slight change in refractive index changes the dispersion. The graining is a manifestation of a different refractive index."

 

[Karl_K]

From another scientist above my pay grade:
"Interesting observation. My take is the colour is there on account of the refractive index at a surface where there is a refraction. A slight change in refractive index changes the dispersion. The graining is a manifestation of a different refractive index."

Interesting,
I have been wondering if defraction was the cause of the graining caused color.
You get a similar effect by superfine lines in machined surfaces.
Some cnc machines are capable of making a silver metal look uniformly blue using the effect.
Defraction grating is the most well known form.

Diffraction grating - Wikipedia

en.wikipedia.org

 

[Garry H (Cut Nut)]

Interesting,
I have been wondering if defraction was the cause of the graining caused color.
You get a similar effect by superfine lines in machined surfaces.
Some cnc machines are capable of making a silver metal look uniformly blue using the effect.
Defraction grating is the most well known form.

Diffraction grating - Wikipedia

en.wikipedia.org

No Karl, the colors are pure dispersion as a result of refracted light entering the diamond.
To see the grain planes there must be visual alignment along the plane direction. But diamond being a hall or mirrors and windows - in any one view there are dozens of angles and orientations.
And because these high res videos are not videos but stitched together real high definition photos - each photo has great depth of field. (I have the original prototype in my museum room).
When a facet goes from seeing no light (dark grey or black) to white light it first passes through a longer violet-blue flash, then the center of the spectrum mixes into white before passing through a short burst of orange red and back to black.

 

[oncrutchesrightnow]

So is your super smart science friend saying the diamond looks “grainy“ because one part of it has a different refractive index than another part? How?

 

[Garry H (Cut Nut)]

So is your super smart science friend saying the diamond looks “grainy“ because one part of it has a different refractive index than another part? How?

Yes, I was not in agreement.
Until I read this on page 210 https://www.gia.edu/doc/WN06A1.pdf

virtually all diamond crystals contain discontinuities in this regular pattern of carbon atoms. For example, plastic deformation is a common feature in natural diamonds. When stress is applied to a diamond above a certain temperature, the crystal lattice is distorted along specific planes. This causes a disruption in the regularity of the crystal lattice that is known as a dislocation, and these dislocations remain after the stress is released (Wilks and Wilks, 1991). The presence of impurities (i.e., other elements, such as nitrogen or boron) will also disturb the packing of carbon atoms in the diamond lattice. In addition, some carbon atoms may not be positioned correctly within the lattice structure. The dislocation of carbon atoms is the predominant cause of graining features in diamond; such dislocations can be introduced either during or after the diamond has formed (Wilks and Wilks, 1991). When these lattice defects or dislocations occur with sufficient density to change the stone’s refractive index or other physical properties, they may create optical disturbances strong enough to be observed with 10× magnification that may have a negative impact on the overall transparency of a faceted diamond.

 

[RunningwithScissors]

This is really interesting, thanks for the discussion on this topic.

 

[Serg]

So is your super smart science friend saying the diamond looks “grainy“ because one part of it has a different refractive index than another part? How?

Graining in Diamond is similar( almost same) phenomena to Stria in Glass .
Below is the link to classical method how to observe stria in glass

https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/10/tie-25_striae_in_optical_glass_us.pdf

 

[oncrutchesrightnow]

Correct me if I’m wrong but isnt the atom displacement what causes pink color diamonds?

 

[Garry H (Cut Nut)]

Graining in Diamond is similar( almost same) phenomena to Stria in Glass .
Below is the link to classical method how to observe stria in glass

https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/10/tie-25_striae_in_optical_glass_us.pdf

Very relevant to your work with lenses for almost every instrument you design and make for rough diamond planning Sergey.
When you polish two small parallel faces on a rough diamond to assess its spectral absorption, is it possible to conduct the pinhole divergent strong light source experiment to identify internal graining?

 

[Garry H (Cut Nut)]

Correct me if I’m wrong but isnt the atom displacement what causes pink color diamonds?

The first quote above is from John Chapman who was for decades the leading scientist working for Argyle. John is the expert and still does not offer a definitive explanation for the pink color. It is related to internal graining and it is possible that there are very very small atoms replacing or messing up the carbon bonding. Possibly hydrogen.