Help to Understand Diamond

[Alvain]

Hi,

I've recently viewed these 2 very similar diamonds from Brian Gavin Diamonds, but I'm very curious about the ASET images.

https://www.briangavindiamonds.com/...0.836-k-vs2-round-diamond-ags-bl-104098251008
https://www.briangavindiamonds.com/...0.800-k-vs1-round-diamond-ags-bl-104098251007

In the ASET for the 0.800 K VS1 (top image) I can see that there are obstructions in between the arrows, which are absent in the ASET for the 0.836 K VS2 (bottom image).



Does anyone have any idea why these obstructions appear? Is it less desirable for diamonds to have these obstructions?

I've only just registered on the forums recently, but the depth of information about diamonds on this forum is simply stunning, especially for someone who is still learning about diamonds so I'm hoping someone can explain this.

Thanks.

Edit - changed the image from left/right to top/bottom, no idea why in preview it was side by side but after posting it changed

 

[diamondseeker2006]

This is not a technical explanation, but every diamond is unique. There will be minute cut differences. This is nothing to worry about and shouldn't be visible to the eye. I think the BG Signature and Black lines may be more strict on cut than the Blue line. But I am sure both stones are fine. I'd honestly be more concerned about the K color.

 

[Alvain]

diamondseeker2006, thanks for the advise but my post is intended to further understand diamond properties rather than a query about the diamonds specifically.

The 2 diamonds used as an example are because they seem rather similar in most aspects, apart from the clarity rating. I am certain that Brian Gavin Blue are cut to very high standards, so it shouldn't be caused by a case of bad cut.

To further illustrate this, these are links to similar diamonds from both Brian Gavin Black line and WF ACA line that shows the obstruction on the ASET.

https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3876802.htm
https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3952890.htm
https://black.briangavindiamonds.com/diamond-details/bkags-104093583056
https://black.briangavindiamonds.com/diamond-details/bkags-104093583055
https://black.briangavindiamonds.com/diamond-details/bkags-104094817007

The common pattern in these diamonds seems to be a 34.9 crown angle. What confuses me is that the following diamonds have the 34.9 CA, but seem to lack these obstructions in their ASET.

https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-2794533.htm
https://black.briangavindiamonds.com/diamond-details/bkags-104092974051
https://www.briangavindiamonds.com/...0.853-h-si1-round-diamond-ags-bl-104098251005

While these diamonds do not have 34.9 CA but still show the obstructions

https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3765676.htm
https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3765677.htm
https://www.whiteflash.com/loose-diamonds/round-cut-loose-diamond-3765678.htm

 

[Krisking]

@Alvain, can you circle what you are seeing in the top image, so we're all on the same page?

 

[diamondseeker2006]

I understand being interested in cut, but I am telling you that every stone will have very minor differences in cut. I would not call it obstruction. It is called contrast. You won't even be able to see these extremely minor differences in a 6mm stone, I promise. See some of the stones and you'll see. There are no negative issues with these tiny image differences in top cut stones. They are not less desirable. I have seen many WF ACAs, for example, and all the ASET images are excellent and all the stones are beautiful in person.

 

[Alvain]

@Krisking, I've circled the obstruction and while doing that I realised i mislabelled the images. The obstructions are in the bottom image, not the top one.

 

[metall]

@Alvain i dont think those are considered obstructions. I think of a spec of carbon as an obstruction, because that is somethung which obstructs the light from coming back. @diamondseeker2006 is correct that evrry stone is cut differently...it is possible that there are some facets that aren't boucing back light. Maybe those facets are cut at a bad angle, maybe the stone was tilted since it appears to only be in the upper half of this image, there are many explanations for this not all of them make this a badly cut stone...

My understanding is that the blue shows areas that do not reflect light back....more leakage than obstruction. But my understanding of how to read these are super limited so I'd be glad if an expert can chime in and verify my assessment.

 

[Krisking]

The obstructions are in the bottom image, not the top one.

Ah, yes, I suspected this was the case.

Yes, blue areas are where light is blocked/obstructed from above (entering from 75-90 degrees) but agree with @diamondseeker2006 that this provides contrast in a well-cut stone. I don't think there is a correlation with CA, but happy to learn more as others chime in.

 

[diamondseeker2006]

The blue is contrast, not leakage. As the stones move, different facets reflect as the light hits them. These are all top of the line stones with outstanding light performance!

 

[Alvain]

@diamondseeker2006 yes you are right, they are all top of the line stones with outstanding light performance.
I am just curious about the cause of these obstructions, hopefully someone who knows about them can chip in.
Personally I would want a diamond without the obstructions just so I can have a clean arrow pattern, but I wouldn't say no to any of these diamonds.

 

[rockysalamander]

I've searched, but can't find the thread where @Karl_K and @John Pollard where commenting on this with technical details. I can't find it, maybe one of them can pop in...

 

[ringo865]

@gm89uk is usually good at this.

 

[diamondseeker2006]

@diamondseeker2006 yes you are right, they are all top of the line stones with outstanding light performance.
I am just curious about the cause of these obstructions, hopefully someone who knows about them can chip in.
Personally I would want a diamond without the obstructions just so I can have a clean arrow pattern, but I wouldn't say no to any of these diamonds.

Please don't keep calling it obstruction, because it is not. It's perfectly fine if you prefer your ASET image to look a certain way. But I can guarantee you if they lined up several stones with the slight variation in images, you would not be able to tell them apart. That was what I was trying to get across.

https://www.whiteflash.com/about-diamonds/diamond-education/about-aset.htm

 

[John P]

Hello @rockysalamander, and all.

Before proceeding, I want to mention that diamond photography is one of the hardest things to execute. Artifacts and aberrations occur with any off-axis between the stage and the camera lens, or the table of the diamond and the lens. This can happen if a truck passes by the building, the heat kicks on at the wrong moment or an annoying cat jumps onto the desk (home office, that one). Even a half-degree off-axis skews details.

So the answer, big picture, will be obstruction/contrast/table-reflection. But the answer to the specific 'circled areas' query is nothing more than a half-degree off-axis of the lens or some unevenness high in the photo setup.

So what are we seeing?

1: Obstruction and Contrast.

Obstruction is the blockage of light coming to the diamond; typically caused by the viewer's head or body in live viewing. The top 30 degrees of the ASET's 180-degree hemisphere is blue. This is designed to re-create a calculated amount of obstruction and helps us analyze the diamond's static contrast pattern.


(AGSL image, used with permission)

Ideally, the lowest facets on the diamond - the pavilion mains - will gather and return light coming from the highest angles above. When well-cut, those mains show as a nicely symmetrical pattern of blue in ASET; aka arrows. This graphic is from a prior thread, but shows how the overall pattern of contrast (and subsequent performance balance) changes as pavilion mains change in width.


(Prior lower-halves discussion here):

Details of length, distribution and how those facets 'play with others' contribute to optical nuances in both the broad character of performance, as well as nuances specific to each diamond.

2: Table Reflection

The circled areas in the ASET images posted above have to do with Table Reflection. Literally, the reflection of the table facet, seen down in the pavilion of the diamond. Diamond cutters used table reflection to judge pavilion depth for generations; long before precision tools and proportions-scanners existed.

Below is a graphic showing how table reflection increases as table size or pavilion depth increase.

Bear in mind these are "perfect" wireframe simulations. In real diamonds, natural variations will skew or bloat the reflection's appearance. As mentioned above, photo off-axis also causes distortions and artifacts. Finally, a given diamond may show slightly less or more table reflection from one photo setup to the next, even in a standardized reflective-cone, based on the orientation of its girdle to the hemispherical base.

• Top examples - Larger tables create wider reflections.
• Center examples - Wider reflections cause central/pooled obstruction ('arrows' are shorter).
• Bottom examples - Increasing pavilion depth also creates wider reflections.

When a diamond is cut so deep that the dark pool of centralized obstruction takes notable prominence the trade calls it a nail-head, describing the dead-dark appearance. Conversely, if the diamond's proportions are so shallow that you start seeing the girdle's reflection in the table, which manifests as a whitish ring, it's called a fish-eye.

I imagine my amphibian friend (shout out @rockysalamander) may have been thinking of prior discussion from this thread.

Now with Obstruction and Contrast info added, above. I hope this is helpful.

 

[ringo865]

Awesome!! This is very helpful and informative. Thanks @John Pollard !!

 

[gm89uk]

My understanding was the blue you have highlighted in the brian gavin stone (the bits between the arrows) are reflections of the star facets.

I've noticed they are more prominent if:
1) The table reflection is bigger (such as with larger tables or higher pavilion angles)
2) Skinnier arrows
3) If Ca/Pa angles combinations are both on the higher end, even in superideal range, such as 35/40.9 combos which BGD commonly are.

I don't think theres any negative impact on real life performance from them.

Like this stone:
https://www.jamesallen.com/loose-di...color-si2-clarity-true-hearts-cut-sku-4297755

 

[Karl_K]

Actually in some of them it is between the areas that show table reflection, it is showing obstruction.
That area(virtual facets) in many combinations is around the zone between red and blue in ASET.
Even some with the same average numbers they can be above or below or some above and some below.
How much obstruction is present and tilt has a huge impact on if it is seen.
In general in most combinations it only shows up if a stone is over obstructed compared to the real word.
It is a total nonissue in real world viewing even if they show which is not the majority of cases.

 

[Alvain]

Thank you for all the explainations. Its really interesting reading through all of the posts and threads (it really took me many rounds of reading just to digest the information!).

Hopefully I'm not understanding it wrongly but from what i gathered, what i observed as obstructions are basically the table reflections caused by virtual facets, hence the blue colour in the ASET. The reason for the irregular pattern of the table reflections are because of either very minor differences in the facets, or a slight angle during photography of said diamond.

Also going through the other threads made me understand that these blue spots in the ASET adds to diamond scintillation. Hence why some people like the thicker arrows caused by shorter girdles. But having too much of these obstructions will cause the diamond to be too dark when they're obstructed by the viewers head (which doesn't happen as often as it sounds) and also may be detrimental to diamond contrast. That being said, i understand these are all still top of the line diamonds that are no different from other top of the line diamonds that don't show these obstructions.

All this reading has now made me interested in virtual facets and their effects in diamond light performance, which unfortunately has very little materials to read through on the internet unlike the nornal facets of a RB diamond.

Once again, thank you for all the kind help. You are all really great people to take the time to educate diamond newbie like me.

Cheers!