Why we prefer ASET to Ideal-Scope with fancy shapes

[JohnQuixote]

[ PS Admin - I was going to put this in FAQ but could not post in that forum. Please move it if appropriate - thanks! ]

If you have ever wondered why experts ask for ASET photos with fancy shapes, here is why:

Reflectors like Ideal-Scope and ASET were developed by diamond manufacturers and researchers in the quest to understand and improve diamond cut quality. They are a fantastic addition to any diamond pro's toolkit. They also form the backbone of the American Gem Society's light performance grade - and are used by cut-focused sellers to prove diamond performance to clients in the sight-unseen internet market.

For those unfamiliar with these tools, here is a good primer: http://www.ideal-scope.com/using_howto.asp

LIGHT RETURN: ROUNDS VS FANCY SHAPES

Round brilliant diamonds are the most efficient at returning light. This means that, regardless of ideal-scope or ASET, rounds will show an abundance of red (or intense light return). In practical terms an ideal-scope image is as telling as ASET for rounds.

But not with fancy shapes. The ASET gives information the ideal-scope does not; it breaks overall light return into less intense areas (green) and more intense areas (red).

WHAT ASET REVEALS


As you see, what's “all-red” in Ideal-scope is broken down into red and green in ASET... Green is not bad - it’s just less intense - but it's important to see this difference. Light return in fancy shapes is not as efficient as it is in rounds (again this is not bad, it’s just physics) so there will naturally be more green in fancies than rounds. Knowing this, we are definitely interested in what areas appear red vs what appears green, so the importance of the ASET image becomes obvious.


EXAMPLE

The two diamonds below are both attractive and they both appear all-red in ideal-scope. Princess 1 is an AGS 0 (Ideal cut grade) with an optimal balance of qualities. Princess 2 is very attractive - a far stronger performer than average commercial options - but you can see from the balance of red and green it is not at the same level of intensity as the AGS 0. There are two different levels of performance here, seen in ASET but not in Ideal-scope.

 

[JohnQuixote]

GENERAL ASET INTERPRETATION

Here is a great reference chart, with motion, on the ideal-scope/ASET site.

Light return (red/green): In fancies we can expect more green than we’re accustomed to seeing in rounds. In fact, there is frequently as much green as red. A balance of red and green is desirable. In some fancy shapes it may be possible to have slightly more red than green, in others it may not be (see footnote*). Motion is more important to performance in fancy shapes than in rounds, and these red and green areas work together to create contrast when the diamond moves.

Obstruction/Shadow (blue): We will see far less blue in fancies than in a round. This is logical since a round brilliant's spoke-like pattern of red (intense light) to blue (light from different, higher angles) drives the vivid on-off sparkle we associate with rounds. Fancy shapes do not have the same contrast in their sparkle, though the princess comes closest. Fancies rely more on movement than rounds for performance precisely because the contrast patterns are more subtle. Look for the balance of red/green to be partnered with areas of blue and small areas of leakage.

Leakage (black): Leakage is black in a non-backlit ASET. The areas are, logically, smaller than they would be in a backlit reflector (where they appear white). In fancy shapes leakage can help create contrast but should be limited.




*Footnote: Just as rounds are more efficient at returning light than the princess cut, other shapes can become less efficient. When shapes become less optimal they show more green than red. Logically, when developing their grading system, the AGSL set different thresholds for different shapes according to what is possible/optimal with the faceting style being considered. As ASET is used increasingly we will see more examples and know what better to expect with, for instance, a radiant or a marquise, compared to a princess or round.

 

[strmrdr]

Directly comparing IS and ASET images is troublesome due too the difference in head shadow built in, in my opinion.
I''m not convinced that 30 degrees is optimal as my asscher work progresses.
It is good for showing the potential for patterns but not as useful as I thought it would be when compared too the real world.
The difference that the amount of head shadow makes is huge with them.
Both IS and ASET can take someone down the wrong path if not carefully applied when it comes to step cuts.

 

[Gypsy]

So John/Storm... can you help me break down my Aset as teaching tool for step cuts? Mine has a LOT of green. Not a lot of red, some blue... and well, other colors going on there too.

 

[strmrdr]

for example a while back I was looking at a .52 ct EC cut the ASET showed perfect patterns but in a stone holder it quickly went dark at other distances and at 20-24" the steps blended.
The stone was too small for the steps to separate at that distance.
Closer and it went dark and further away it went dark in other areas.
While I still find it useful it is not that final answer I was hoping it would be.
Jon has also found some AGS5 light performance asschers that blow away AGS0 light performance asschers in the real world.

 

[strmrdr]

Date: 12/7/2007 1:25:51 PM
Author: Gypsy
So John/Storm... can you help me break down my Aset as teaching tool for step cuts? Mine has a LOT of green. Not a lot of red, some blue... and well, other colors going on there too.

It looks like too me that the stone wasnt in the proper position in the scope.
Areas that should be blue are red and orange.
Stone positioning is absolutely critical with step cuts even a fraction of a mm can make a huge difference.

 

[JohnQuixote]

Date: 12/7/2007 1:23:34 PM
Author: strmrdr
Directly comparing IS and ASET images is troublesome due too the difference in head shadow built in, in my opinion.
I'm not convinced that 30 degrees is optimal as my asscher work progresses.
It is good for showing the potential for patterns but not as useful as I thought it would be when compared too the real world.
The difference that the amount of head shadow makes is huge with them.
Both IS and ASET can take someone down the wrong path if not carefully applied when it comes to step cuts.

It takes a lot of work. I'm constantly patting the guys in our photo dept on the back for evolving both of these tricky systems. We've got pretty good repeatability in terms of obstruction (though ASET has proved more tricky and sometimes acquiring focal depth means getting closer, means increasing degrees of obstruction). One of the hardest things about ASET photos is getting proper focus and good color resolution. Because of the multiple colors the lighting is much more tricky than Ideal-Scope, which is one of the most user-friendly tools we have.

Also Strm, don't forget that diamond size can also confound setups. When you get near 8mm and over it can require a whole reset/rethinking of things, particularly making sure girdle alignment is proper as crown height gets unusualy large in face-down situations.

Bear in mind also that this thread is intended as a FAQ/primer (read the first sentence), particularly for shapes like princess, not a treatise. The purpose of the thread is to demonstrate what ASET shows that IS does not.

 

[JohnQuixote]

Date: 12/7/2007 1:25:51 PM
Author: Gypsy
So John/Storm... can you help me break down my Aset as teaching tool for step cuts? Mine has a LOT of green. Not a lot of red, some blue... and well, other colors going on there too.

You win the prize Gypsy. Step cuts are more difficult than brilliants and mixed cuts in reflectors. That is not surprising, since their appeal is not necessarily in the intensity of light return, but more subtle qualities like pattern and fire.

Rounds, ovals, princess cuts, etc. are far more readable - in both ideal-scope and ASET.

The lighting in your photo was a bit strong which is causing colors to mix in some interesting ways.

 

[Gypsy]

Date: 12/7/2007 1:51:50 PM
Author: JohnQuixote

Date: 12/7/2007 1:25:51 PM
Author: Gypsy
So John/Storm... can you help me break down my Aset as teaching tool for step cuts? Mine has a LOT of green. Not a lot of red, some blue... and well, other colors going on there too.

You win the prize Gypsy. Step cuts are more difficult than brilliants and mixed cuts in reflectors. That is not surprising, since their appeal is not necessarily in the intensity of light return, but more subtle qualities like pattern and fire.

Rounds, ovals, princess cuts, etc. are far more readable - in both ideal-scope and ASET.

The lighting in your photo was a bit strong which is causing colors to mix in some interesting ways.

Does this one help?

 

[JohnQuixote]

Date: 12/7/2007 1:54:27 PM
Author: Gypsy

Date: 12/7/2007 1:51:50 PM
Author: JohnQuixote

Date: 12/7/2007 1:25:51 PM
Author: Gypsy
So John/Storm... can you help me break down my Aset as teaching tool for step cuts? Mine has a LOT of green. Not a lot of red, some blue... and well, other colors going on there too.

You win the prize Gypsy. Step cuts are more difficult than brilliants and mixed cuts in reflectors. That is not surprising, since their appeal is not necessarily in the intensity of light return, but more subtle qualities like pattern and fire.

Rounds, ovals, princess cuts, etc. are far more readable - in both ideal-scope and ASET.

The lighting in your photo was a bit strong which is causing colors to mix in some interesting ways.

Does this one help?

It's more clear/consistent - and backlit (thus showing light areas I feel are exaggerated) - but this shape is one that really must be seen to make a decisive call. This has nothing to do with performance, but the patterns are wonderful. Beautiful cutting.

Sorry Gypsy, I think I should have been more clear in my initial purpose - which is to delineate why we like ASET with the most common cuts (princess especially). Step cuts are a different world - as are cushions in my opinion - and while we feel confident in meaningful interp of round, princess, oval & radiants to a large degree in reflectors I would still prefer live eyes to IS or ASET for a step cut... The appealing qualities are entirely different than the intense performance we look for in modern brilliant/mixed cuts.

 

[FireGoddess]

Great thread John! I thought this would be a good place to bring up a question I posed recently but nobody answered...what DOES a good pear ASET look like? Any pictures? I''ve never seen an example of a model pear ASET, which would be helpful since it is a fancy cut and they never perform stellarly on IS.

 

[chrono]

Good question FG. I''d like to see one for each shape (oval, EC, pear, marquise, princess, etc). Even a simulated picture is fine.

 

[Gypsy]

Date: 12/7/2007 2:25:56 PM
Author: JohnQuixote

Date: 12/7/2007 1:54:27 PM
Author: Gypsy

Date: 12/7/2007 1:51:50 PM
Author: JohnQuixote

Date: 12/7/2007 1:25:51 PM
Author: Gypsy
So John/Storm... can you help me break down my Aset as teaching tool for step cuts? Mine has a LOT of green. Not a lot of red, some blue... and well, other colors going on there too.

You win the prize Gypsy. Step cuts are more difficult than brilliants and mixed cuts in reflectors. That is not surprising, since their appeal is not necessarily in the intensity of light return, but more subtle qualities like pattern and fire.

Rounds, ovals, princess cuts, etc. are far more readable - in both ideal-scope and ASET.

The lighting in your photo was a bit strong which is causing colors to mix in some interesting ways.

Does this one help?

It''s more clear/consistent - and backlit (thus showing light areas I feel are exaggerated) - but this shape is one that really must be seen to make a decisive call. This has nothing to do with performance, but the patterns are wonderful. Beautiful cutting.

Sorry Gypsy, I think I should have been more clear in my initial purpose - which is to delineate why we like ASET with the most common cuts (princess especially). Step cuts are a different world - as are cushions in my opinion - and while we feel confident in meaningful interp of round, princess, oval & radiants to a large degree in reflectors I would still prefer live eyes to IS or ASET for a step cut... The appealing qualities are entirely different than the intense performance we look for in modern brilliant/mixed cuts.

OK. Thanks John.

So step cuts, as we all knew before... still REALLY REALLY need to be seen and chosen with the eyes. Fair enough! And I appreciate the clarification!

I''m interested in FG''s question too!

 

[Rhino]

Hey John,

The topic caught my attention. I really appreciate your attention to this especially for us fellow cut and techy geeks. While I would agree ASET information is great to have I''m finding that there are some stones with seemingly great reflector images be skankers especially in way of fancies. Something I''ve noted in the past and would maintain is that while reflectors are great for determining reflectors/non reflectors of the atmosphere surrounding the diamond, the red ones and even ASET does not always tell an accurate determination of head/body obstruction. I''ve recently had some diamonds (asscher) in my hands from 1ct to 2ct with ASET images that looked impressive (even scoring "0" on the PGS) but upon examination weren''t quite the best. There are also stones with great ASET images that are drop dead gorgeous too. As with all technologies I find none are the end all be alls. Sorry I can''t stick around here longer to participate but wondering if you''re finding the same thing. I have this thread bookmarked.

Have a great season.

Peace,
Jon

 

[stebbo]

Date: 12/7/2007 4:17:27 PM
Author:JohnQuixote
EXAMPLE
The two diamonds below are both attractive and they both appear all-red in ideal-scope. Princess 1 is an AGS 0 (Ideal cut grade) with an optimal balance of qualities. Princess 2 is very attractive - a far stronger performer than average commercial options - but you can see from the balance of red and green it is not at the same level of intensity as the AGS 0. There are two different levels of performance here, seen in ASET but not in Ideal-scope.

Did you have the pic for this John?

 

[JohnQuixote]

Date: 12/7/2007 3:16:44 PM
Author: FireGoddess
Great thread John! I thought this would be a good place to bring up a question I posed recently but nobody answered...what DOES a good pear ASET look like? Any pictures? I''ve never seen an example of a model pear ASET, which would be helpful since it is a fancy cut and they never perform stellarly on IS.

Thanks FG.Here are images of a first-class pear.

In this case it was helpful to have IS and ASET because there is glare at the head, wing and point of the diamond in the ASET image.By looking at the backlit IS photo we could tell they were just artifacts of the ASET setup and better identify them.

 

[JohnQuixote]

Date: 12/7/2007 6:14:44 PM
Author: Gypsy

OK. Thanks John.

So step cuts, as we all knew before... still REALLY REALLY need to be seen and chosen with the eyes. Fair enough! And I appreciate the clarification!

No problem Gypsy.

Another thing which must be kept in mind: We are using one standardized system. That''s very important to understand - splitting hairs with these images isn''t possible source to source because right now there is no corss-platform uniformity... If we were to raise or lower the diamond it could change the angular spectrum and therefore some of the dividing lines between red/green by several degrees. We work very hard to align the girdle plane with the tip of the reflector (IS/ASET) which is one reason we perform our shots face-up and try to shoot same-sizes (if we have two dozen diamonds to shoot we group them according to size for consistent placement, and adjust as we do). There are versions of IS and ASET where the diamond rests face-down on a plate of glass and the camera shoots upward. Although this negates the tilt sometimes seen in face-up setups it also aligns the table of the diamond with the reflector, rather than the girdle plane, so that other adjustments (in fractions of mm) must be made if girdle-plane alignment is the goal.

With all that said, if I had the choice (from any source) between an IS or ASET photo for fancy shapes I''d still take the ASET because it gives more information. And, given a known setup, I would prefer to have both if possible.

 

[JohnQuixote]

Date: 12/8/2007 10:40:53 AM
Author: Rhino
Hey John,

The topic caught my attention. I really appreciate your attention to this especially for us fellow cut and techy geeks. While I would agree ASET information is great to have I''m finding that there are some stones with seemingly great reflector images be skankers especially in way of fancies. Something I''ve noted in the past and would maintain is that while reflectors are great for determining reflectors/non reflectors of the atmosphere surrounding the diamond, the red ones and even ASET does not always tell an accurate determination of head/body obstruction. I''ve recently had some diamonds (asscher) in my hands from 1ct to 2ct with ASET images that looked impressive (even scoring ''0'' on the PGS) but upon examination weren''t quite the best. There are also stones with great ASET images that are drop dead gorgeous too. As with all technologies I find none are the end all be alls. Sorry I can''t stick around here longer to participate but wondering if you''re finding the same thing. I have this thread bookmarked.

Have a great season.

Peace,
Jon

We do. Shapes with brilliant pavilion faceting are much more predictable in ASET than step cuts. I''d say my level of confidence using IS/ASET in a known setup to make (for example) firm buying decisions would be round/princess for sure, followed by oval/radiant at a fairly high confidence level. Other shapes, particularly step cuts, I''d need to see in person. This is all hypothetical since we look at every stone we would offer to a consumer but I''m happy with the evolution we''ve seen.

Since you mention it, we''ve also been experimenting with obstruction in step cuts. Garry gave us a heads-up when he saw some things going on that looked far too dark. Come to find that we were creating about 45 degrees of obstruction in some of those images.

In general (maybe because we see so many more) our scanning & photography from A-Z with rounds & princess cuts is more standardized/seamless than other shapes.

 

[Garry H (Cut Nut)]