Simple Science: Is shallow or deep better?

[Garry H (Cut Nut)]

For the record – the ideal stone is 1.06ct H VS2 and has a 55.3% table, 34.9° crown and 40.75° pavilion with virtually no painting or digging. The shallow stone is 59.5% table, 31.3° crown and 40.6° pavilion with some creative digging on 2 sides to remove some naturals. The Gem Adviser file for the ideal stone is attached and I am happy to send the full DiamCalc and Helium scan data to anyone by email.

You may need to download the free Gem Adviser software if you dont have it already - it is amazing that such a tool can be made free - so f you dont have it - please get it - you can find the links under tools> DiamCalc in the upper right of this page.

 

[Garry H (Cut Nut)]

If you have not read the previous 3 posts on the other page - please do so first.

The shallow stone is 1.03ct D SI2 with 59.5% table, 31.3° crown and 40.6° pavilion with some creative digging on 2 sides to remove some naturals. The ideal stone is 1.06ct H VS2 and has a 55.3% table, 34.9° crown and 40.75° pavilion with virtually no painting or digging. The Gem Adviser file for the shallow stone is attached and I am happy to send the full DiamCalc and Helium scan data to anyone by email.

You may need to download the free Gem Adviser software if you dont have it already - it is amazing that such a tool can be made free - so if you dont have it - please get it - you can find the links under tools> DiamCalc in the upper right of this page.

In an ideal world I would have used a steep deep in that steep deep ear ring survey, but I do not have any in stock and it seems unfair to local vendors to take their goods out of circulation.

 

[Rhino]

Hey Garry,

Just thought I''d add a little graphics to concur your study as I''m reading through your 2nd portion and point #6.

6. A diamond is like a set of windows and mirrors; it can concentrate and let you see lots of different light sources around you. Steep Deeps gather more light from the mid part of the imaginary lighting hemisphere above a diamond. If you look top down on a steep deep diamond (with stone facing the ceiling) in a normal room, then much of your line of vision will be directed to the area between the top of the windows and the ceiling - so you will see less bright sparkles. You can understand this best by using OctoNus / Moscow State Uni cool tool http://www.cutstudy.com/cut/english/comp/scint1.htm - you can see where the lights can come from on an imaginary screen placed between you and the diamond. Please change the step button at the top to 0.3 degrees, and starting with a shallow default proportions, increase the pavilion angle 1 click at a time. You will note the specks move out away from the center of the screen as the stone gets deeper. Deeper stones return window light better to your eye and shallow stones are best able to return light from the ceiling. I used this software as part of HCA development. (Rhino please do this as it will help you understand a critical issue that you have been ignoring).

Here is an ASET image confirming your statement regarding typical steep/deeps drawing their light from the horizon as opposed to directly from above if I''m reading you right. For clarification the greens represented in this image indicates portions of the diamond that are drawing light from the 0-45 degree zone, or when observed with the diamond facing the ceiling and the observer looking down upon the diamond, would represent light entering from windows etc. In most circumstances this is what AGS considered sources of reflected light (like off of walls etc.) as opposed to direct light from above.

7. AGS chose a middle path for its new grading system - preferring Tolkowsky ‘ideal’ over shallower stones. AGS think that to be a good diamond should not become dark until more than 22% or 40° of lights in a hemispheres are obscured (by our head and or body). I think 15% or 27° is an adequate amount of light to block. This is why I disagree with AGS:

I hear what you''re saying here Garry but the issue of how much obstruction is a tricky issue at best. The reason I say this is because of each individual''s focal length. The folks we''ve been surveying, if I were to take a rough estimate vary in focal length anywhere from 6-7 inches and as far as 14 inches. A shallow stone will appear darker to most observers who have short focal lengths as the pavilion facets in shallow stones, although functioning as mirrors, are redirecting too much reflection from the observer and back to the observer... hence more darkness. This has and always will be my problem with shallow stones. On the other hand ... a person with a longer focal length (such as myself) and this issue is minimized resulting in exactly what you''re pointing out. A stone that will gather its primary reflections from the bright lighting above providing for a very bright stone. I''d attach another graphic to demonstrate but I''ll have to in my next post to demonstrate this if I can find the darn graphic.

a. Whenever we look at a diamond we are attratced by ''good'' features such as bright sparkles. Each eye can see different sparkles, because we have 2 eyes and each has a different vantage point, we sometimes see twice as many sparkles than we would with only 1 eye (this bit is for you Storm

). But any diamond with nice sparkles that also has large ugly features will be thought to be a bad looking stone, even if it has plenty of sparkles. But to be rejected BOTH eyes must see the BAD zone (

)– if only one eye sees it, and the other sees a sparkle from that region, then that zone is good. (And that is why I need to soften HCA on the slightly steep deep border)

I personally think this is a move in the right direction mate. Of course it depends whether you want the HCA to reflect critical analysis of the steep deeps (akin to AGS approach of steep/deeps) or one that agrees more with human observation (akin to GIA''s approach). Perhaps both ... a small notation on the HCA stating that in a critical analysis stones over 2.0 do have leakage under the table but stones up to x.x will not have leakage visible to the human eyes using stereo vision.

On a personal level I''d like to see the same done with the shallow/shallow combos but i know your personal preference towards those and since you are the developer of it, will reflect your personal tastes.

b. AGS’s effectively set an observer with a 6 inch (15cm) head viewing from 9 inches (22cm) as the level of obstrucring or light sources. This was a fundemental mistake - like the one I made with HCA - because it is the model for a ‘cyclops’ single eyed viewer. As Bruce Harding (who invented the concept in 1975) points out, each eye only has a smaller amount of obscuration (10 degrees) from the left and right, and top of our heads blocks about 25° - up to perhaps 35° with a big hair style. This means that the only part of a shallow diamond that would appear dark or could not sparkle is that part which would have lights obscured by our body. And guess which type of diamond is most prone to having lights blocked by our body? You guessed it – the Steep Deep stone that gathers lots of light from lower angles.

I hope I still have you all?
Is there any questions etc before we move to part 3 (where I twist the knife)

Good stuff man.

Peace,

 

[Rhino]

One other note about the shot you took of the earrings. In the shallow stone on the left you can see more darkness or darker zones due to the obstruction of the camera and photographer being close to the stone. I''m not sure if that shot demonstrates clearly the point your trying to bring out (if you''re trying to demonstrate brightness). If the camera and photographer were pulled back from the stone more I think it might help a bit Garry. I took the shot and lightened it up a bit to see the contrast between the lighter and darker areas.

I see what you''re saying though about the dirt that accumulated on the stones.

 

[Rhino]

Date: 4/26/2006 8:34:24 PM
Author: Modified Brilliant

Date: 4/26/2006 2:31:59 PM
Author: Rhino

Date: 4/24/2006 10:24:40 PM
Author: jasontb
Looks like the ASET is angry and giving me the bird.

LMAO ... I saw that too!

The side effects of using the ASET...who knows what other images will arise?

www.metrojewelryappraisers.com

Yea... too funny Jeff. Hey ... while I''ve seen you around on the boards I don''t think I''ve ever introduced myself to ya. It''s a pleasure to make your acquaintance and good to have another active trade member around.

Kind regards,

 

[Modified Brilliant]

Thanks, Rhino.

Good to be active on PS.

www.metrojewelryappraisers.com

 

[Rhino]

Hi Garry,

I seem to recall these same diamonds being discussed at an earlier time and think I have models of these along with a 1.07ct FIC? The 1.03ct being what you describe as a BIC and the 1.06ct as the TIC? Are these part of your master set?

 

[Garry H (Cut Nut)]

Thanks for taking the time to read and digest this Rhino

Date: 4/27/2006 8:34:47 PM
Author: Rhino
Hey Garry,

6. A diamond is like a set of windows and mirrors; it can concentrate and let you see lots of different light sources around you. Steep Deeps gather more light from the mid part of the imaginary lighting hemisphere above a diamond. If you look top down on a steep deep diamond (with stone facing the ceiling) in a normal room, then much of your line of vision will be directed to the area between the top of the windows and the ceiling - so you will see less bright sparkles. You can understand this best by using OctoNus / Moscow State Uni cool tool http://www.cutstudy.com/cut/english/comp/scint1.htm - you can see where the lights can come from on an imaginary screen placed between you and the diamond. Please change the step button at the top to 0.3 degrees, and starting with a shallow default proportions, increase the pavilion angle 1 click at a time. You will note the specks move out away from the center of the screen as the stone gets deeper. Deeper stones return window light better to your eye and shallow stones are best able to return light from the ceiling. I used this software as part of HCA development. (Rhino please do this as it will help you understand a critical issue that you have been ignoring).

Here is an ASET image confirming your statement regarding typical steep/deeps drawing their light from the horizon as opposed to directly from above if I''m reading you right. For clarification the greens represented in this image indicates portions of the diamond that are drawing light from the 0-45 degree zone, or when observed with the diamond facing the ceiling and the observer looking down upon the diamond, would represent light entering from windows etc. In most circumstances this is what AGS considered sources of reflected light (like off of walls etc.) as opposed to direct light from above.
thanks - it makes the point well

7. AGS chose a middle path for its new grading system - preferring Tolkowsky ‘ideal’ over shallower stones. AGS think that to be a good diamond should not become dark until more than 22% or 40° of lights in a hemispheres are obscured (by our head and or body). I think 15% or 27° is an adequate amount of light to block. This is why I disagree with AGS:

I hear what you''re saying here Garry but the issue of how much obstruction is a tricky issue at best. The reason I say this is because of each individual''s focal length. The folks we''ve been surveying, if I were to take a rough estimate vary in focal length anywhere from 6-7 inches and as far as 14 inches. A shallow stone will appear darker to most observers who have short focal lengths as the pavilion facets in shallow stones, although functioning as mirrors, are redirecting too much reflection from the observer and back to the observer... hence more darkness. This has and always will be my problem with shallow stones. On the other hand ... a person with a longer focal length (such as myself) and this issue is minimized resulting in exactly what you''re pointing out. A stone that will gather its primary reflections from the bright lighting above providing for a very bright stone. I''d attach another graphic to demonstrate but I''ll have to in my next post to demonstrate this if I can find the darn graphic.

I think when you read the point you posted below in 6b. it becomes apparent that the stereo vision thing cuts both ways

a. Whenever we look at a diamond we are attratced by ''good'' features such as bright sparkles. Each eye can see different sparkles, because we have 2 eyes and each has a different vantage point, we sometimes see twice as many sparkles than we would with only 1 eye (this bit is for you Storm

). But any diamond with nice sparkles that also has large ugly features will be thought to be a bad looking stone, even if it has plenty of sparkles. But to be rejected BOTH eyes must see the BAD zone (

)– if only one eye sees it, and the other sees a sparkle from that region, then that zone is good. (And that is why I need to soften HCA on the slightly steep deep border)

I personally think this is a move in the right direction mate. Of course it depends whether you want the HCA to reflect critical analysis of the steep deeps (akin to AGS approach of steep/deeps) or one that agrees more with human observation (akin to GIA''s approach - Hey that comes a bit close to demagogy

). Perhaps both ... a small notation on the HCA stating that in a critical analysis stones over 2.0 do have leakage under the table but stones up to x.x will not have leakage visible to the human eyes using stereo vision.

On a personal level I''d like to see the same done with the shallow/shallow combos but i know your personal preference towards those and since you are the developer of it, will reflect your personal tastes.

that is the whole point of this article Rhino - that here is an example of a very shallow stone that is right on the lowest HCA ranking for ideal of 2.0 - an extreme stone (that I have kept for a while and think I might have used it before) that even has wonky symmetry - this stone performs really well and is a great example of why I hold the shallow stone belief. You might have even done an observer test and preffered it - in Drena''s earring at Vegas last year?

b. AGS’s effectively set an observer with a 6 inch (15cm) head viewing from 9 inches (22cm) as the level of obstrucring or light sources. This was a fundemental mistake - like the one I made with HCA - because it is the model for a ‘cyclops’ single eyed viewer. As Bruce Harding (who invented the concept in 1975) points out, each eye only has a smaller amount of obscuration (10 degrees) from the left and right, and top of our heads blocks about 25° - up to perhaps 35° with a big hair style. This means that the only part of a shallow diamond that would appear dark or could not sparkle is that part which would have lights obscured by our body. And guess which type of diamond is most prone to having lights blocked by our body? You guessed it – the Steep Deep stone that gathers lots of light from lower angles.

I hope I still have you all?
Is there any questions etc before we move to part 3 (where I twist the knife)

Good stuff man.

Peace,

 

[Garry H (Cut Nut)]

Date: 4/27/2006 8:43:34 PM
Author: Rhino
One other note about the shot you took of the earrings. In the shallow stone on the left you can see more darkness or darker zones due to the obstruction of the camera and photographer being close to the stone. I''m not sure if that shot demonstrates clearly the point your trying to bring out (if you''re trying to demonstrate brightness). If the camera and photographer were pulled back from the stone more I think it might help a bit Garry. I took the shot and lightened it up a bit to see the contrast between the lighter and darker areas. i thank you for the effort Rhino - but I am not using these photo''s to show the difference in cut quality - that shot was taken hand held at night in a big room with only 6 dull halogens - on my desk at home in the lounge / family room with my Ixus 40 Canon holiday snap camera. The other photo''s too have too much camera darkness - but were taken with a serious camera we just bought in a new prof flash set up - but much too much surrounding darkness (the same Diamond Dock problem - very bright flash makes the rest of the room effectively very very dark) - not to mention the big black camera lens.

I see what you''re saying though about the dirt that accumulated on the stones. That was an entirely unintended consequence of this study - if you have some steeper deepers - you should try making the pavilion dirty - I expect they will show the dirt a lot more.

 

[Garry H (Cut Nut)]

Continuing on with the study (but all interjections are valued).

Here we see the shallow stone on the left and the ideal cut on the right. In the ideal-scope and the center row of ASET photo’s, the ideal cut has Hearts and Arrows quality symmetry, where as the shallow stone does not have such good symmetry (which is also evident in the gem file models).

In the middle ASET photo we can see that the table region of the shallow stone is predominately blue (except for a green central table reflection). The ASET provides blue light from the upper 30 degree region (17% of the hemisphere above the girdle), red down to 45 degrees and green from there to the horizon..

The bottom ASET photo’s were taken via a mock up ASET with some reflective dark blue cardboard added to imitate the observers body. Some of you think this looks a bit like “giving the bird” (which I had to look up to understand – it is not an Aussie saying). At the base this blue area covers approximately 65° or 18% of the available light and this strip tapered slightly to the top of the scope. The “bird” look comes because I inserted two small strips of bright pink paper either side of the lens hole, covering part of the blue. This is to account for the small angular difference or around 10° of obstruction of lighting that two eyed people could expect at a very close distance (rather than the Cyclops 30° that AGS used).

Notice now that there is about the same amount of blue in the shallow stone than the ideal cut?
May I repeat that - it is very important.

The shallow and ideal cut stones have about the same amount of blue or obstruction of lighting when seen through a scope that models a Human observer.

I did not know that until I started this study - which I have been doing as we progress.
I think this is amazing. But then I am easily amazed

 

[Garry H (Cut Nut)]

Here is the ASET scope with a piece of metallic blue card board and 2 slivers of hot pink card stuck in.

I could not get a bright enoung blue card - that is why I used the matallic stuff which the stationary shops seem to all stock.

I say this because I want anyone to be able to repeat this experiment.

And if anyone wants to get an ASET scope they can contact AGS diectly, or order through me or Dave Atals and we will supply them for $50 plus delivery.

The photography is easy too - all you need is our light tray ($30) and an ordinary inexpensive digital camera - they seem to work better than flash ones with big lenses. Dont use macro - do use Tungstin (the light bulb icon). There is a section - the bottom of the newsletters on ideal-scope tells you how.

 

[yeewl]

Hi Garry,

I am keen to find out more regarding the ASET scope and had send an email to enquire.


Kind regards

 

[pricescope]

Garry, how the dimensions of the blue insert relate to the real life: eye to diamond distance, head size, etc?

 

[oldminer]

You can make a case for shallow OR deep diamonds based on cost savings / asking price alone. There is a trade-off either in performance, durability or apparent size. Take your choice, these other depths do not give the balance of factors that the near Tolkowsky rounds provide. This doesn''t mean that deep or shallow diamonds can''t provide a beautiful appearance sufficent to make someone decide on a compromise. Remember, people don''t choose D-IF commonly, and there are good, valid reasons why they don''t.

Deep or shallow diamonds have features which are problematic when compared to well cut diamonds, but that does not mean the problems are serious enough to say you''d never consider the benefits that they also may offer. Garry has pointed out that shallow diamonds look larger and may not suffer much in light performance under certain conditions.

The idea of a miniature man shadow in the ASET scope is a pretty good concept. Now, what does it mean commercially? It depends on the size of the shadow, the distance of the observer, etc. I might argue the ASET scope, unaltered, provides meaningful data on its own, without further variables tossed in.....K.I.S.S. is the motto.

 

[Garry H (Cut Nut)]

Dave this shallow stone has a thick indestructable girdle and inspite of so so symmetry it outsparkles the near perfect Tolkowsky Ideal and has a better spread. In what way is this stone a compromise?
True the market would expect the shallow stone to be 10-15% less costly. But maybe the market is not as smart as it thinks it is?

Date: 4/29/2006 7:27:33 AM
Author: oldminer
You can make a case for shallow OR deep diamonds based on cost savings / asking price alone. There is a trade-off either in performance, durability or apparent size. Take your choice, these other depths do not give the balance of factors that the near Tolkowsky rounds provide. This doesn''t mean that deep or shallow diamonds can''t provide a beautiful appearance sufficent to make someone decide on a compromise. Remember, people don''t choose D-IF commonly, and there are good, valid reasons why they don''t.

Deep or shallow diamonds have features which are problematic when compared to well cut diamonds, but that does not mean the problems are serious enough to say you''d never consider the benefits that they also may offer. Garry has pointed out that shallow diamonds look larger and may not suffer much in light performance under certain conditions.

The idea of a miniature man shadow in the ASET scope is a pretty good concept. Now, what does it mean commercially? It depends on the size of the shadow, the distance of the observer, etc. I might argue the ASET scope, unaltered, provides meaningful data on its own, without further variables tossed in.....K.I.S.S. is the motto.

The KISS ASET works great for fancy shapes Dave - have you tried yours with many fancies?
But I find the Ideal-scope is all I need for rounds.

 

[jasontb]

I''ve got some questions/observation for you Garry. Hopfeully the regions in cirlced in yellow will show up well:

You covered up some of the blue in the original ASET scope with pink. This has a big effect on the image. It takes a LOT of blue in the table of the shallow stone and turns it red. What is the real-world justification for this particular modification to the scope? It seems to be having a bigger impact than the ''miniature man shadow''. I don''t think the difference would be nearly as noticible if you left that part alone and just added the ''miniature man shadow''. Did you try it like that? What made you choose this way?

All the assymetry in the modified-ASET of the ideal stone hurts. It''s hard to process IMHO. The blue regions between the arrows in the original ASET image: Based on other reflector and ray-tracing images, I''ve come to *expect* to see those. But the modified ASET only shows them on one half of the stone. So when you added pink to top of the ASET you turned all those regions pink. Then you added the miniature man shadow and turned half of them back blue. I''m having a hard time understanding that.

I think the modified ASET gives you a good idea of what the stone will look like in one particular setup (one set of: diamond position, observer position, lighting position). Sort of like a worst case scenario ASET. But there could be 20 other observers standing around looking at the stone...and there observations of the stone would be more closely mimiced by the KISS ASET, no?

 

[Garry H (Cut Nut)]

Thanks Jason - by asking me for clarification it helps me to polish up what I hope will become a useful article.

I am not suggesting that i will be selling or recomending the Human ASET - it is an exercise to simply show that the current thinking that says shallow stones are bad is flawed by one simple fact - we have 2 eyes that are not in the center of our heads.

Date: 4/29/2006 3:07:26 PM
Author: jasontb

You covered up some of the blue in the original ASET scope with pink. This has a big effect on the image. It takes a LOT of blue in the table of the shallow stone and turns it red. What is the real-world justification for this particular modification to the scope? It seems to be having a bigger impact than the ''miniature man shadow''. I don''t think the difference would be nearly as noticible if you left that part alone and just added the ''miniature man shadow''. Did you try it like that? What made you choose this way? The Blue was covered up to represent the approximate 10 degrees of angular distance between each eye and the side of our head on the same side as that eye. AGS used 30 degrees in the design of that ASET scope that I made for them. So I left the same 30 degrees to the top of the virtual human - and covered the part that made a model of 10 degrees each side - i.e. cover 1/3rd red, 1/3rd blue and 1/3rd red - but I am sure you will agree that I covered less than 1/3rd - because I did not want to be accused of cheating to prove my point - so probably I have covered about 8 degrees each side.

All the assymetry in the modified-ASET of the ideal stone hurts. It''s hard to process IMHO. The blue regions between the arrows in the original ASET image: Based on other reflector and ray-tracing images, I''ve come to *expect* to see those. But the modified ASET only shows them on one half of the stone. So when you added pink to top of the ASET you turned all those regions pink. Then you added the miniature man shadow and turned half of them back blue. I''m having a hard time understanding that. The slightest rotation of the Human ASET changes the symmetry - it is just an exercise Jason - just an exercise.

I think the modified ASET gives you a good idea of what the stone will look like in one particular setup (one set of: diamond position, observer position, lighting position). Sort of like a worst case scenario ASET. But there could be 20 other observers standing around looking at the stone...and there observations of the stone would be more closely mimiced by the KISS ASET, no? Of course - but from each observers point of view the HumanASET would show the stones potential.

I am also working on the actual body size etc as Leonid / Pricescope mentioned above.
If the stone is right up close to your body then half the ASET on one side should be blue. The further away from your body - the thinner the blue part should be.

 

[strmrdr]

The bird aset would be ok if the light was coming from behind the person but it usualy isnt.
Most lighting is high angle from above or low angle from the sides.

 

[Garry H (Cut Nut)]

Sitting at a desk with hand in front, on a key boad for example.

 

[strmrdr]

more complete lighting map for that stone., not allowing for backlight which is this case could make a large difference.

 

[Garry H (Cut Nut)]

Date: 5/1/2006 12:12:30 AM
Author: strmrdr
more complete lighting map for that stone., not allowing for backlight which is this case could make a large difference.

Unfortunately the computer screen is blocking the wiindow light that might have entered the pavilion Storm

Here is that schematic layout with the ASET coulrs around the outside and the position of the GIA strip lights and defuser. this is what the colors were to represent on your slide?

But I am briniging another thread and discussion here - as this topic is not about Diamond Dock.

 

[strmrdr]

standard aset angles green and red. the blue zone would be close to the persons head location.

yea but getting some light from the monitor also.

I was trying to demo that the appearance of that diamond wouldn't be that simple to calculate.
I can picture the diamonds appearance in my head but dont have the energy tonight to DC it.
I did play enough to tell that the other light sources are going to have a large impact on the diamonds appearance.

Thinking about it the ASET's strength is that is doesn't duplicate one lighting scheme it tells you what angle the diamond is drawing light from then you can take that info and apply it
For example in that lighting a diamond with lots of green could be brighter than one that was mostly red because the the diamond would draw in more of the low angle lighting and return it.

 

[Garry H (Cut Nut)]

If the light only comes from that region a Tolkowsky will look like this - well if the light was coming from the floor too.

Green is not a great direction for nice looking stones.

 

[Garry H (Cut Nut)]

But on the other hand the Stone Jonathon filmed in DD would look pretty good.

 

[beryl]

Garry has asked me to comment but I can offer little of value since I do not deal with diamonds and diamond customers on a daily basis. The title "Simple Science" is erroneous; it is not 'simple' because there are so many interacting factors, and it is not 'science' because the conclusions are subjective.
In Part 2, 6 Garry mentions some software by Octonus/MSU, which shows the 'sources' of reflections to the viewer's eye. I suggest also the 'LightMap' feature in Anton Vasiliev's software 'Facet Design', which shows these dots on a movable spherical surface. This software is available free and has been included on recent discs from AGS. A tutorial is under 'Help'.
In Part 2, 7b he mentions my 10° angle of obstruction for one eye to that side of the head. This was a hasty measurement at the time and rounded-off to 10°; more precise measurements are given on the attached diagram ('DiamondTalk' circa Jan 2003). The exact angle is unimportant; the "Faceting Limits" charts of 1975 could ultimately have been a series of curves for different angles = a 'topographic' chart of different 'levels', much like MSU and GIA later did with their 3D studies.
I am pleased to see that Octonus abandoned the cyclops eye and has addressed stereo vision. My 'DiamondTalk' thread of 2003 showed that each eye sees something different. Meaningful discussions of diamond appearance must consider this factor.
If you review "Faceting Limits" (reprints now available from GIA - Gems & Gemology, Fall 1975), you will see that the historically-evolved 'best' cuts for all stones were along the upper edge of the upper black diagonal band (10° obstruction of bezel-table rays) ... EXCEPT that for topaz and tourmaline they are on the opposite edge of this band - in Zone B! These are indeed shallow stones; has anyone ever cut a diamond with Zone B proportions? A sequel (never published) showed that stones cut in Zone B had the advantage that body shadows were distributed across the entire stone, rather than concentrated on one side or the other, as when cut in Zones A or C. Perhaps this is a factor in the appeal of shallow diamonds to Garry.
One DiamCalc illustration in an article-in-progress accidentally showed much light entering the pavilion and exiting the crown. This is not a bad thing. In Part 2, 1 Garry refers to 'rubbed-in' settings. I have never heard that term and assume that he means what we call 'bezel-set' or antique books call 'collet-set'. I gave up doing this and always talked the customer out of doing it because, sooner or later, somehow, liquid gets through and under the stone and then there is no way to clean it.
EDIT: Oops - sorry - my first GIF submittal via Word Processor picture editor.

 

[beryl]

Here is one illustration from that 'DiamondTalk' thread circa Jan 2003 - for only internal rays from bezel-to-table. Red rays are those reflected to one eye, blue to the other eye; note that they come from opposite sides of the head. Clearly each eye sees something different; what does the brain see?

 

[beryl]

Here is an interesting illustration from Newsletter 03 to Anton Vasiliev''s"Facet Designer". See the dots on the sphere which indicate the direction of light sources that will reach the viewer''s eye (at left) The sphere is Gilbertson-colored but has been rotated 180° so that the red is above the culet and the black above the girdle, but viewing with table toward the eye. I think you cannot do this with ASET scope.
In this case I was showing where the light comes from that appears as wedges around the edge of the diamond.
I digress, Garry, because of your mention of the Octonus/MSU thing in Part 2, 6; I think the readers will enjoy this.

 

[beryl]

This illustration from the "Facet Designer" tutorial is of special interest to the subject of head and body image. The size of the head (red arrows) can be adjusted and the body (green arrows) can be turned on or off. Additionally, an environment can be superimposed, such as the desert scene here (blue arrows). You can then rotate the gem within this environment.
Sorry for the poor quality: I cannot find the original illustrations and do not have time to re-create them, so I scanned a print-out of the tutorial. Nevertheless you can see the power of this software and the fun you can have with it - free!

 

[Garry H (Cut Nut)]

Thanks Beryl, I appreciate your stopping by

Date: 5/2/2006 10:50:08 PM
Author: beryl
I suggest also the ''LightMap'' feature in Anton Vasiliev''s software ''Facet Design'', which shows these dots on a movable spherical surface. This software is available free and has been included on recent discs from AGS. A tutorial is under ''Help''.
Where can we find this Beryl?
In Part 2, 7b he mentions my 10° angle of obstruction for one eye to that side of the head. This was a hasty measurement at the time and rounded-off to 10°; more precise measurements are given on the attached diagram (''DiamondTalk'' circa Jan 2003). The exact angle is unimportant; the ''Faceting Limits'' charts of 1975 could ultimately have been a series of curves for different angles = a ''topographic'' chart of different ''levels'', much like MSU and GIA later did with their 3D studies.
I am pleased to see that Octonus abandoned the cyclops eye and has addressed stereo vision. My ''DiamondTalk'' thread of 2003 showed that each eye sees something different. Meaningful discussions of diamond appearance must consider this factor.
Agreed - By the way you have a tilt mewntioned in the lower left of that scheme Beryl? The tilt would not change the angular relationships would it?
If you review ''Faceting Limits'' (reprints now available from GIA - Gems & Gemology, Fall 1975), you will see that the historically-evolved ''best'' cuts for all stones were along the upper edge of the upper black diagonal band (10° obstruction of bezel-table rays) ... EXCEPT that for topaz and tourmaline they are on the opposite edge of this band - in Zone B! These are indeed shallow stones; has anyone ever cut a diamond with Zone B proportions? A sequel (never published) showed that stones cut in Zone B had the advantage that body shadows were distributed across the entire stone, rather than concentrated on one side or the other, as when cut in Zones A or C. Perhaps this is a factor in the appeal of shallow diamonds to Garry.
I need to study up on the article before I comment Beryl - here is a link well into the article folks -click the Table of Contents to return to the start http://www.cutstudy.com/cut/english/faceting/f5.htm
One DiamCalc illustration in an article-in-progress accidentally showed much light entering the pavilion and exiting the crown. This is not a bad thing. In Part 2, 1 Garry refers to ''rubbed-in'' settings. I have never heard that term and assume that he means what we call ''bezel-set'' or antique books call ''collet-set''. I gave up doing this and always talked the customer out of doing it because, sooner or later, somehow, liquid gets through and under the stone and then there is no way to clean it.
I do mean bezel set, sorry, but bezels are almost always open from behind for easyier cleaning than prongs. The other thought I had re4ading your response Bruce is that pavilions are almost always dirty - see my earlier photo''s after just 1 weeks build up - and this would diffuse the light entering the pavilion. Intuitively I believe that would not create fire. What do others think?

 

[Garry H (Cut Nut)]

Date: 5/2/2006 11:57:28 PM
Author: beryl
Here is an interesting illustration from Newsletter 03 to Anton Vasiliev''s''Facet Designer''. See the dots on the sphere which indicate the direction of light sources that will reach the viewer''s eye (at left) The sphere is Gilbertson-colored but has been rotated 180° so that the red is above the culet and the black above the girdle, but viewing with table toward the eye. I think you cannot do this with ASET scope.
In this case I was showing where the light comes from that appears as wedges around the edge of the diamond.
I digress, Garry, because of your mention of the Octonus/MSU thing in Part 2, 6; I think the readers will enjoy this.

Anton was doing amazing stuff with colored gems when I first met him some years back in Moscow.

How come these Russians are so brainy?
You are right - cant see the leakage that way unless the light is coming THROUGH the walls of the ASET - and they are opaque - I can sort of see the effect with an ideal-scope reflector sitting on a light box.
But a single color is easy on DC.