Simple Science: Is shallow or deep better?

[Garry H (Cut Nut)]

Topic: Simple Science: Is shallow or deep better?

Often diamond choice comes down to dollars – with many complex trade-offs. This just as true for you, the consumer, as it is for a diamond cutter planning the proportions to polish each rough diamond. Here on Pricescope many people would prefer a very tight set of “Tolkowsky” or “ideal” proportions; but this limit’s the cutters options to achieve a desirable and important carat weight yield. I would like to facilitate better economics for cutters and consumers and help ensure more of those choices lead to more sparkly diamonds.

I seem to have become the champion of slightly shallow diamonds, and the enemy of slightly deep ones. I have debated this with many experts. And many disagree with me.

But many peoples buying decisions are influenced by my opinion via HCA results, so it seems like a good idea to explain the pro’s and con’s of shallow and deeper diamonds in simple terms.

First let’s consider some reasons why I may be wrong:

1. On the side in favour of the slightly deep stones the leading Russian scientist and developer of DiamCalc, Sergey Sivovolenko, has persuaded me that years ago I placed too much importance on leakage apparent through the Ideal-Scope:
   
   
   
   1. Ideal-scope images are a single eyed top dead center view - when each of our 2 eyes sees the stone from about 5 degrees of tilt from the left and the right - slightly leaky stones look less leaky. This image attempts to show the 'canceling out' of steep deep stone with leakage caused by stero-scopic vision. The first row shows the same virtual diamond as it would appear from the top with black, gray and white backgrounds. Notice the dark ring of leakage inside the table on the black background? On the second row notice that from the left eye’s and the right eyes point of view there is less leakage. The combined central image is an attempt to show why our 2 eyes do not see such a bad looking dark leakage zone.
      
      
   2. Just because a diamond has some leakage does not mean that it can not have very great light return. Most fancy shapes have a lot more leakage, but people still like them. And some slightly steep deep diamonds (say +0.5 degree pavilion angle to 41.25°) still have very good DiamCalc computed light return.
      
      
   3. The ideal-scope and all colored reflector scopes exaggerate leakage (it is a human color intensity perception issue).
   
   
2. When set in high 4 claw ring settings deep leaky stones are able to get some light from underneath and behind - so the leakage zones do not look too dark- and light sources from partial leakage are from light entering close to the critical angle - which can emerge out the crown as broadly dispersed firey flashes.
   
   
3. Young couples (<30) buying engagement rings often focus from very close up (from less than 6 inches – 15cm) – they may reject shallow stones because the table region can look dark because their head is so close it blocks light sources.
   
   
4. Fish eye’s are usually shallow stones. But not always; a fish eye effect is a result of a combination of pavilion angle, table size and to a lesser extent crown height and girdle thickness. For instance a diamond can have a 57% table size and less than 59% depth and still not show a Fish-eye.

 

[jasontb]

Oooh...this should be a fun thread. I'm assuming you are preparing a second post now. So maybe you are about to answer this question, but I'll ask it anyway:

What's going on in the third and fourth rows? I'm assuming that rows 2, 3, and 4 are (from left to right) left eye, stereo, and right eye views of the stone with (from top to bottom) black, grey, and white backgrounds. And are all the images of the same stone?

 

[strmrdr]

Iv seen far more deep diamonds than shallow and even ideal cuts but it would depend on the setting and application.
For a ring in an open setting - slightly deep
For a pendant or earring or for someone with poor eyesight - slightly shallow

very deep and very shallow are equally nasty.

The main reason to stick in the ideal range is that across a wider range of lighting, environment and eye-sight they while maybe get beat in some conditions they in general work well across them all.
more later...

 

[Serg]

Hi, Garry

Great Post.

You forgot about 5th reason -Fire.

 

[Garry H (Cut Nut)]

Date: 4/23/2006 1:42:18 AM
Author: Serg
Hi, Garry

Great Post.

You forgot about 5th reason -Fire.

I have found quantifying fire to be very difficult.
Both types of dark zones (in shallow and in deep diamonds) seem to display good fire - often more than Tolkowsky.

BTW I edited point #2 to add about fire
There is more to come Sergey

 

[strmrdr]

Iv done similar experiments with deep stones than Leonid and Jim did where the dead zone becomes much more apparent if you blocked light from the pavilion.
When looking at used stones at re-sales shops before I got the aset and IS one of my checks was to block all the light thru the pavilion with my fingers then check the stone.
A long while back I had noticed the difference but it wasn''t until I got the IS that I clued in on why this was happening.
In local stores the settings tend to be high and finding a low setting in a preset ring is hard, I has asked my local guy who does a lot of setting for the stores why this was and he said that most stones look better with some light entering the pavilion.
Most of the stones he sets are steep/deep because its the most common combo out there.

 

[oldminer]

As I prefer old European cuts, as a general group, over other less than Ideally cut stones, I fall on the side of slightly deeper stones being preferable to thin ones. Deeper stones tend to be more durable and if you find they fit your budget, you are getting what you see. They don''t lose their brilliancy as rapidly with dirt accumulation on their pavilions, too.

This does not mean very steep/deep diamonds are great looking. It does not mean that a matched collection of rather shallow diamonds, properly set into an appropriate setting won''t look perfect for the job.

It means that, within reason, deeper diamonds are overall my preference to shallow ones, if I must choose other than very well cut and well proportioned options.

 

[diagem]

For some reason, i would also prefer deeper stones than their shalow counterpart, especialy in fancy shapes.

What i mean, i like to see more "crown height" in diamonds, my opinion that they are more reflective, and more desirable when set in jewelry.

I would not prefer the pavilion angles to be cut deeper, since in my opinion thats where the brilliance starts..., but in fancy shapes you have quite a lot of options to play with the "pavilion faceting structure", which you dont have in rounds.

dont get me wrong, i have seen some amazing looking "shallow" fancy shaped diamonds, but in my opinion they are a rare find..., a cutter must have LOADS of experience and know-how to cut these shallow diamonds, and unfortunatly most cutters dont.

But larger and steeper crown facets with smaller tables are my fancy...

 

[Rhino]

Love it Garry. Admittedly I was taken in with your opinion against steep/deep stones particularly with pavilion angles at and over 41 degrees. When conducuting our last survey I admittedly had a natual bias against them but I did not let any of the observers see any reflector images, proportions or any detailed data before the observations. This is no secret as I''ve been counseling against *any* steep/deep combo''s over the course of the past 6 years that I''ve been participating on these forums and my inventory reflects this as well. My survey''s with these have changed my opinion as well as listening to Sergey''s input regarding our own stereo vision and how it was that consumers were picking a GIA Ex steep/deep over the other stone we were using in our survey.

The question that begs an answer in my own mind at this time is how steep/deep can one go without seeing too much degradation in optical characteristics such as brightness, fire and scintillation.

What''s even more funny to me on a personal level is I am just about done with my response to your journal article and some of the points you are bringing up in this thread are precisely some of the things I am pointing out in my response. There is also something in your graphics in this thread that represent the truth of what you are pointing out which is also brought out in your photography in your article which I will share in my response which I don''t think you realized when you were taking those photographs.

BTW, when diamonds fall outside of the AGS Ideal/GIA Ex range on the shallow end the optics of the diamond are impacted in an entirely different way than what will happen when they tend towards the steep/deep side and outside of AGS/GIA ideal zones I certainly have a preference.

Keep it coming Garry.

 

[He Scores]

As a cutter, my experience and learning is that a "fisheye" is a product of a shallow bottom main angle, usually beginning around 39 degrees. It has nothing to do with depth/spread ratio. Certainly a larger table will expose it more readily.

As for Old Euro''s. Prior to sawing diamonds, which gave us the "production" stone of a shallow top (usually around 33 degrees) and a 41 bottom, stones were cut to the top/bottom ratios of the common crystals that diamond rough was found. So not all old cuts have the same steep/deep whatevers.

You would generally find from the majority of the crystals, stones that would be "high on top and high on bottom" (octahedron), high on top and flat on bottom (dodecahedron) or flat on top and flat on bottom (macle).

Another concern is that most cutters will agree that the higher the bottom angle is over 40.75 degrees, the darker the middle of the stone is.

Go ahead...talk amongst yourselves.

Bill Bray
Diamond Cutter

 

[Garry H (Cut Nut)]

Date: 4/23/2006 7:48:30 PM
Author: He Scores

As a cutter, my experience and learning is that a ''fisheye'' is a product of a shallow bottom main angle, usually beginning around 39 degrees. It has nothing to do with depth/spread ratio. Certainly a larger table will expose it more readily.

Bill Bray
Diamond Cutter

Bill you are correct that the pavilion is the main decider of fish-eye, and i am certainly not proposing pavilion angles of 39 degrees.

For a crown angle of 34.5 and table 57% a 39 degree pav is a fish eye.
The same level of fish eye is achievable with a 40.75 pavilion and a 69% table.
The same amount of fish eye occours at 40 pav and 64% table.

But as the girdle gets thicker the fish eye becomes much more apparent.

Date: 4/23/2006 7:48:30 PM
Author: He Scores
As for Old Euro''s. Prior to sawing diamonds, which gave us the ''production'' stone of a shallow top (usually around 33 degrees) and a 41 bottom, stones were cut to the top/bottom ratios of the common crystals that diamond rough was found. So not all old cuts have the same steep/deep whatevers.

You would generally find from the majority of the crystals, stones that would be ''high on top and high on bottom'' (octahedron), high on top and flat on bottom (dodecahedron) or flat on top and flat on bottom (macle).

Another concern is that most cutters will agree that the higher the bottom angle is over 40.75 degrees, the darker the middle of the stone is.

Bill Bray
Diamond Cutter

Agreed - a lot of old cuts are nice. 33 / 41 with a 60 table (bigger than the old cuts) is one of the best selling combinations that optimizes size and brightness in my retail sales experiance. i call it a BIC

 

[Rhino]

Hey Garry,

Your images above got me thinking ...

Have you had a chance to check out this stone in DiamCalc and view with 3d glasses in the stereo vision 3d mode? I wonder how/if the view would corellate? Heh... now I gotta go find me a pair of those geeky 3d glasses.

 

[Garry H (Cut Nut)]

Not enough seperation to make any difference

I have broken this article into 3 parts because there is a lot to learn.
Now for PART 2

Against Steep Deep's:

1. Steep deeps show a dark ‘ring of death’ zone just inside the table when they are set in rubbed in settings (you can see that in the top left image in the first post), or pendants, earrings and very low ring settings, because no light can get in the leakage area. We identify this as a negative effect in larger diamonds; in very small diamonds our eye can not resolve the ugly dark ring.

2. This dark zone produces fewer bright sparkles (but fire can be good from this zone in high open set rings – see the little image below in the top left corner of the big picture).

3. They have a smaller spread. HCA is the only grading system I know of that includes spread as a ‘grading factor’. Other systems, like the new AGS and GIA ones simply knock stones down from the top grade if they are more than 5% smaller than Tolkowsky or deeper than 63%. I choose to make a shallow HCA ideal stone as the starting yardstick; this means a Tolkowsky stone gets a small spread penalty (about 0.2) but the steepest deepest GIA Excellent gets a spread penalty of about 1.0.

4. Steep Deeps look worse when they are dirty. Grease and oily films are attracted to diamonds more than any other substance on earth (diamond has the highest surface tension). This affects the stone bottom or pavilion more because in daily wear the grease does not get rubbed off the stone bottom.

5. These 2 earrings have been worn and alternated for 1 week without the pavilions being cleaned (the tops have been wiped). The shallow stone on the left looks much cleaner than the stone on the right which is close to ideal. because of the dirt the ideal stone is duller and returning less light from the crown facets.

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).

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:

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)

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)

 

[valeria101]

Two questions on the side of the existing text:

- Between the two earring stones, which is what (shallow vs deep) ?

- About setting recommendations: what is a ''high'' or open setting by definition (i.e. in terms of light''s access to diamond). Also, when the right time comes along the main story... what would be the recommended proportions for a closed setting (say, rub over - no light from the pavilion & easy to clean).

Thanks

Looking forward to the follow up

 

[Garry H (Cut Nut)]

Date: 4/24/2006 2:05:33 AM
Author: valeria101


Two questions on the side of the existing text:

- Between the two earring stones, which is what (shallow vs deep) ?Sorry Ana - I edited the text to correct it - the stone on the left is shallow. After i have all the photo''s i will clean them both and do a Helium scan and post the GemAdviser Files

tions: what is a ''high'' or open setting by definition (i.e. in terms of light''s access to diamond). Also, when the right time comes along the main story... what would be the recommended proportions for a closed setting (say, rub over - no light from the pavilion & easy to clean).

I happen to know that you are an expert at finding ring pihoto''s and I am sure you could easily describe and show examples of low rings that obscure light - and high settings that allow light to enter the pavilion.

Storm has alerted me to what I knew but never processed in my mind - USA has for a long time been the home of deeper cuts with smaller tables and thicker girdles (much of the rest of the world prefers big tables and flatter stones) - so it is no surprise that higher stones can better in US settings than those from the rest of the world (which are probably on average half to 2/3rds as high, and far more likely to be 6 prong settings than 4 claw.

Thanks

Looking forward to the follow up

 

[valeria101]

Me and my unclear questions...

Sure I can find examples of closed settings... was only wondering what type of RBC (between the shallow, ideal and deepish ones discussed here) would be recommended. I have been living with the illusion that stones with slightly shallow pavilion angles (around 40 degrees) and higher crowns & smaller tables (to prevent fisheye) work best. And hoped to check on this belief with the occasion.

The story about US settings did answer though - I am a bit more used with the European styles, and ''twice as high'' also implies prongs wide apart and the pavilion of the diamonds hanging away of the hand''s shade. Kind of baffling choice, IMO.

 

[strmrdr]

Here is an example from walmart that is typical of rings found locally.
I see very few low Tiffany styles they are med and high.
Notice the large airspace under the diamond.
Even 6 prong settings will be set high.

http://www.walmart.com/catalog/product.do?product_id=4253116

 

[strmrdr]

larger diamond, 6 prong.
http://www.walmart.com/catalog/product.do?product_id=2036739

 

[strmrdr]

http://www.walmart.com/catalog/product.do?product_id=2189021

Earrings.

 

[Garry H (Cut Nut)]

Date: 4/24/2006 7:14:16 AM
Author: strmrdr
http://www.walmart.com/catalog/product.do?product_id=2189021

Earrings.

Thanks Storm.
The high rings are excellent examples.
And even the ring with the thick girdle - girdles also are very effective (but not weight efficient) facets in well cut rounds.
This ray trace shows how a faceted extremely thick girdle can direct light back in a useful direction.

The earrings sit too close to the head and are not usually able to get much pavilion light.

 

[Garry H (Cut Nut)]

Part 3:
In favor of Shallow stones:
1. Better spread for a given carat weight.
2. Out side facet light return is usually much better, so perceived spread is even bigger.
3. Shallow stones are much less affected by grease and dirt.
4. Shallow stones look great in earrings, pendants and rubbed in ring settings where no light can get in from behind. Steep Deeps have a dark ring in that region.
5. The same reason that 2 eyed views improve the look of steep deep stones, also helps our perception of the brightness of shallow stones. i.e. because our eyes are close to the side of our heads, our heads block a lot less light from surrounding sources than the Cyclopian''s would have us believe.
6. Shallow stones worn in rings sparkle more in ceiling lighting than deep stones.
7. If we made an ASET type scope with a model of a person with the width to each eye and a body (obstructing lights) in blue, then shallow stones would look better in this scope than deeper diamonds. This proposed ASET from the inside view is shown on the left and the inside of an actual ASET is on the right.

 

[jasontb]

Looks like the ASET is angry and giving me the bird.

 

[Garry H (Cut Nut)]

LOL Jason.

I am not at work - but just shot a very slightly deep diamond and a small so so CZ through each of these ASET scopesb (one mocked up roughly to show what I mean).

I think it is evident that there is more blue in the regular ASET than is shown in the Human Body ASET.

If I had a deeper stone I expect it would show a lot more blue in the new improved scope.

 

[Garry H (Cut Nut)]

Oops - I hate doing that

 

[Garry H (Cut Nut)]

Here is an actual phot of the mock up

 

[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!

 

[oldminer]

Thought it was a cyclops at first. Then I saw the nasty! oooh! This is never going to be the "standard"?

 

[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

 

[Garry H (Cut Nut)]

Shallow / Ideal Dirty Earring Study

I temporarily set 2 diamonds into a pair of studs and asked one of my staff to wear them for a week, moving them from 1 ear to the other each day, and not cleaning them. One stone is shallow 1.03ct D SI2 and the other is a nice ideal cut diamond 1.06ct H VS2. The diameters are almost identical.

After being worn for a week I gave them to about a dozen people to hold and asked them to tell me which they preferred, and after they answered, if one stone appears larger. This was not a formal survey, and the lighting was not always the same, although many people chose to, or I directed them to look in various lighting types.

All, except one male in a dark suit and dim café lighting, preferred the shallow stone and all thought it appeared larger.

Most observers held the stones about 14 - 20 inches from their eyes and close to or several inches from their body with lights overhead, or up higher with daylight behind them.

These photographs show the thin film or greasy dirt on the pavilion of the stones. The crowns of the stones were relatively clean.

 

[Garry H (Cut Nut)]

And here is the top view photo’s - with deep stones on the right, the crown facets were wiped clean.
See the dirt?

What surprised me was that the ideal cut stone (right) showed more dirt around the crown facets than the shallow stone. The ideal cut stone also showed a little more dirt when seen on an oblique angle through the table; but this is what I expected to see, as steep deep diamonds show this effect very strongly.