Diamond Cut Angles

[soontomarry]

Per the advice of many of the very knowledge people here on pricescope, I am planning to get the best cut possible on the diamond I am soon to purchase.

While looking through multiple websites, I found these suggested cut values on niceice.com:

Total depth between 59 - 61.8%
Table diameter between 53 - 57%
Crown angle between 34.3 - 34.8 degrees
Pavilion angle between 40.6 - 40.9 degrees
Girdle thickness between thin and slightly thick
Culet: AGS pointed or GIA none

Is it generally agreed that a diamond in this range will have the best cut possible with all the wonderful light characteristics that come with it?

Are there any other values that should be kept in check other then these listed?

While looking at the GIA report on some "ideal" diamonds on bluenile.com, I notice that some of the values fall out of this range. Seemingly the value which most often falls out of this range is the pavilion angle. Many of the pavilion angles on stones listed on bluenile.com go above 40.9 degrees. Is the pavilion angel range above to restrictive?

Thanks for our help!

 

[Lorelei]

Date: 2/28/2010 9:36:54 AM
Author:soontomarry
Per the advice of many of the very knowledge people here on pricescope, I am planning to get the best cut possible on the diamond I am soon to purchase.

While looking through multiple websites, I found these suggested cut values on niceice.com:

Total depth between 59 - 61.8%
Table diameter between 53 - 57%
Crown angle between 34.3 - 34.8 degrees
Pavilion angle between 40.6 - 40.9 degrees
Girdle thickness between thin and slightly thick
Culet: AGS pointed or GIA none

Is it generally agreed that a diamond in this range will have the best cut possible with all the wonderful light characteristics that come with it?

Are there any other values that should be kept in check other then these listed?

While looking at the GIA report on some 'ideal' diamonds on bluenile.com, I notice that some of the values fall out of this range. Seemingly the value which most often falls out of this range is the pavilion angle. Many of the pavilion angles on stones listed on bluenile.com go above 40.9 degrees. Is the pavilion angel range above to restrictive?

Thanks for our help!

Hi STM

Those are indeed Todd from niceice's parameters that he uses for selecting a diamond, they are pretty tight but they serve him extremely well for his business in order to narrow the field of well cut stones. You can certainly work with those as an initial screening tool along with images such as Idealscope, or you can expand on those if you prefer as there can be well cut stones that fall outside of these ranges, it depends on how you want to approach it.

I can post another list of proportions you can use if you want to see those too, also you can use the Holloway Cut Advisor to help you, generally look for stones which score between 1 and 2 initially.

There can be far more flexibility with pavilion angles than with crown angles, once you start going much over 41 degrees then various undesirable issues can be of concern so I would suggest keeping pavilions between 40.6 - 41 degrees and with GIA bear in mind this number is rounded so always get images to evaluate the quality of the cut and the overall cutting precision.

 

[FB.]

I think that perhaps your table % is slightly small - the optimum is more like 55-57%.

Otherwise, your proportion shortlist is good and pretty safe.

GIA's top grade is rather wide-ranging. Most on here would argue that GIA should have a grade above "Excellent" - perhaps called "Ideal" - which would include proportions in the heart of GIA's "Excellent" grade.

But that's not to say that other proportions won't work - it's just that they are more difficult for the cutter to get to work.
It's like an "optimisation" curve, with your shortlist of proportions being in the "sweet spot".
At the top of the curve (the sweet spot), small variations or rounding errors in proportions make little difference to performance. As you move away from the peak of the curve, small differences in proportions make a big difference to performance.

 

[stone-cold11]

No, not ncessary, because the numbers on a report is the average numbers of 8 measurements for table, crown and pavilion angles and then rounded off to the nearest step size. It is useful as a first cut off for further examination with images, IS/ASET etc.

If IS/ASET is available, you can generally dismiss the numbers.

53-57% table is too restrictive, the angles are the most important part of the equations, as long as they are complimentary, tables up to 60% can still be a great cut, just have a slightly different appearance than the smaller tables.

 

[Dreamer_D]

https://www.pricescope.com/cutadviser.asp

Here is a link to the cut advisor. It is a good idea to plug in the numbers of any diamond you are considering and see if it scores les than a 2. If it does, it is worth further consideration either with an IS or other images, or if you can see the diamond in person, with careful visual inspection and comparison with other contenders in many different lighting environments.

Also note that the labels given to diamonds by diamond vendors, like "Signature ideal" etc, are not as important as the cut grade on th ecert.

 

[Rockdiamond]

I would strongly advise looking at actual stones rather than using the guide you refer to. For sure I would avoid using grades given to cut by the sites which offer the diamonds themselves, and stick to GIA EX ( or VG) or AGS0
Many in the trade- including GIA's own EX cut grade include other proportions you might find more visually pleasing.
Personally I like a table in the 60% range which seems to "open up" the top of the stone allowing more brilliance.

 

[Lorelei]

Date: 2/28/2010 10:42:15 AM
Author: FB.

There is FB! Missed you here!

 

[ChunkyCushionLover]

Date: 2/28/2010 9:36:54 AM
Author:soontomarry
Per the advice of many of the very knowledge people here on pricescope, I am planning to get the best cut possible on the diamond I am soon to purchase.

While looking through multiple websites, I found these suggested cut values on niceice.com:

Total depth between 59 - 61.8%
Table diameter between 53 - 57%
Crown angle between 34.3 - 34.8 degrees
Pavilion angle between 40.6 - 40.9 degrees
Girdle thickness between thin and slightly thick
Culet: AGS pointed or GIA none

Is it generally agreed that a diamond in this range will have the best cut possible with all the wonderful light characteristics that come with it?

Are there any other values that should be kept in check other then these listed?

While looking at the GIA report on some ''ideal'' diamonds on bluenile.com, I notice that some of the values fall out of this range. Seemingly the value which most often falls out of this range is the pavilion angle. Many of the pavilion angles on stones listed on bluenile.com go above 40.9 degrees. Is the pavilion angel range above to restrictive?

Thanks for our help!

I agree with Rockdiamond, these ranges are very restrictive and are one posters opinion on the best performing diamonds to them. This is a very safe range where if you had no other tools like reflector images or HCA these ranges could be used.

You would also be safest staying with the strict range of AGS0 cut grading because GIA Excellent is a much wider range, however the majority of posters prefer a more general approach listed below:

1) Put the numbers from the certificate including crown and pavilion angle, depth % and table% into HCA https://www.pricescope.com/cutadviser.asp it will tell you if the combination of crown and pavillion angles work well together.

2) All stones scoring under HCA <2. may be ideal cut diamonds with no leakage.

3) For any stones scoring HCA <2 check symmetry and leakage using an Idealscope http://www.ideal-scope.com/1.using_reference_chart.asp

There are many Pricescope vendors that provide Idealscope images already posted on their site or upon request.
If you post any of your potential choices in this thread other posters can help evaluate the light performance of your selection(s).

 

[FB.]

Date: 2/28/2010 10:59:05 AM
Author: Lorelei

Date: 2/28/2010 10:42:15 AM
Author: FB.

There is FB! Missed you here!

I come and go......
If I have nothing useful to add, then I stay quiet.........you know the trouble that I cause sometimes.

 

[Lorelei]

Date: 2/28/2010 12:20:02 PM
Author: FB.

Date: 2/28/2010 10:59:05 AM
Author: Lorelei

Date: 2/28/2010 10:42:15 AM
Author: FB.

There is FB! Missed you here!

I come and go......
If I have nothing useful to add, then I stay quiet.........you know the trouble that I cause sometimes.

LOL! I am glad to see you back!

 

[FB.]

Date: 2/28/2010 12:35:47 PM
Author: Lorelei

Date: 2/28/2010 12:20:02 PM
Author: FB.

Date: 2/28/2010 10:59:05 AM
Author: Lorelei

Date: 2/28/2010 10:42:15 AM
Author: FB.

There is FB! Missed you here!

I come and go......
If I have nothing useful to add, then I stay quiet.........you know the trouble that I cause sometimes.

LOL! I am glad to see you back!

But I bet you''ve got that rolling pin out of the drawer again - just in case.

 

[WinkHPD]

Date: 2/28/2010 10:42:15 AM
Author: FB.

I think that perhaps your table % is slightly small - the optimum is more like 55-57%.

Otherwise, your proportion shortlist is good and pretty safe.

GIA''s top grade is rather wide-ranging. Most on here would argue that GIA should have a grade above ''Excellent'' - perhaps called ''Ideal'' - which would include proportions in the heart of GIA''s ''Excellent'' grade.

But that''s not to say that other proportions won''t work - it''s just that they are more difficult for the cutter to get to work.
It''s like an ''optimisation'' curve, with your shortlist of proportions being in the ''sweet spot''.
At the top of the curve (the sweet spot), small variations or rounding errors in proportions make little difference to performance. As you move away from the peak of the curve, small differences in proportions make a big difference to performance.

I am very curious how you come up with this? For those of us who like lots of dispersion the 53% tables should definitely be in this spread. It is the original table size that Tolkowsky suggested in his original description of the Ideal cut. Why do you dismiss it?

Wink

P.S. To soontomarry, it is this type of disagreement between posters that shores up the absolute necessity for you to see many diamonds and quality of cuts and decide which of them appeal the most to YOUR eyes.

 

[FB.]

Wink

Why 55-57% table?

Only because they are more "agreeable" to a wider selection of people.

The more fiery/less bright (less fiery/larger spreading (>57%) cuts tend to be a rather acquired taste that not everyone prefers.

 

[FB.]

Didn''t Tolkowsky''s theory use an extremely thin girdle?
I thought that once a medium girdle was added, the table size was optimum at 56%.

Could be wrong though......

 

[WinkHPD]

Date: 2/28/2010 1:42:30 PM
Author: FB.
Didn''t Tolkowsky''s theory use an extremely thin girdle?
I thought that once a medium girdle was added, the table size was optimum at 56%.

Could be wrong though......

I would not say you were wrong about what YOU prefer, but since AGS still allows those parameters in its grading I would say you were wrong to exclude what might be what I prefer.

Even though I am a well known advocate for Ideal cut diamonds, and more particularly for what some call the "super Ideal" cut diamonds, I try to recognize and respect that those are my preferences and that each person should see the diamond that he/she thinks may be the one that they want with a clear and not too quick time to inspect and accept or inspect and reject.

Wearing a diamond is about what makes the wearer happy. All of us here try to help the help seekers understand what is available and what will be in the normally accepted parameters of incredible cutting, but still, the wearer needs to be able to see and agree or reject the final choice.

Many of us love the fire, and many of us prefer more brilliance. Both are acceptable within the confines of the AGS 0 cut grade, so I am uncomfortable seeing anyone try to say they are not correct without a solid reason why.

Wink

 

[Karl_K]

Todd''s list is good if you want to stay near tolk.
There are many other great ranges than near tolk.
BIC FIC 60/60(a subset of them anyway) 41/34 and others.

Near tolk is a safe zone and the biggest zone so it is easy but it is not the only one.

 

[FB.]

Wink,

Perhaps I was wrong to exclude what you prefer. I also have a liking for fiery stones.
But where do we draw the line for the mainstream?

Evidently, some people like GIA EX "steep/deep" - especially because it often inverts or suppresses the black/white contrast appearance of the arrows/pavilion facets.
Are we wrong to exclude steep/deep?

Would we be wrong we wrong to exclude 60/60, just because you or I prefer 52/62?
My OH loves the look of the 60/60, 33/41 type.

My suggestion for 55-57 table was to stay right in the heart of GIA EX, so that most people will not be unhappy.
I agree that some people would prefer FIC or BIC - but if they''re not viewing in person, FIC or BIC is too risky.

I wuold say to people; by all means buy a 53% or a 59% table, but make sure that you like the way it will look. By choosing a 56% table, you''re in a reasonably safe zone.

 

[Chase035]

Date: 2/28/2010 1:13:59 PM
Author: Wink

Date: 2/28/2010 10:42:15 AM
Author: FB.

I think that perhaps your table % is slightly small - the optimum is more like 55-57%.

Otherwise, your proportion shortlist is good and pretty safe.

GIA''s top grade is rather wide-ranging. Most on here would argue that GIA should have a grade above ''Excellent'' - perhaps called ''Ideal'' - which would include proportions in the heart of GIA''s ''Excellent'' grade.

But that''s not to say that other proportions won''t work - it''s just that they are more difficult for the cutter to get to work.
It''s like an ''optimisation'' curve, with your shortlist of proportions being in the ''sweet spot''.
At the top of the curve (the sweet spot), small variations or rounding errors in proportions make little difference to performance. As you move away from the peak of the curve, small differences in proportions make a big difference to performance.

I am very curious how you come up with this? For those of us who like lots of dispersion the 53% tables should definitely be in this spread. It is the original table size that Tolkowsky suggested in his original description of the Ideal cut. Why do you dismiss it?

Wink

P.S. To soontomarry, it is this type of disagreement between posters that shores up the absolute necessity for you to see many diamonds and quality of cuts and decide which of them appeal the most to YOUR eyes.

What is meant of dispersion in lower table values like 53 and 54%?

 

[Chase035]

Plenty of 53% and 54% tables are TIC, not FIC, no?

 

[WinkHPD]

Date: 2/28/2010 2:55:17 PM
Author: Chase035

Date: 2/28/2010 1:13:59 PM
Author: Wink

Date: 2/28/2010 10:42:15 AM
Author: FB.

I think that perhaps your table % is slightly small - the optimum is more like 55-57%.

Otherwise, your proportion shortlist is good and pretty safe.

GIA's top grade is rather wide-ranging. Most on here would argue that GIA should have a grade above 'Excellent' - perhaps called 'Ideal' - which would include proportions in the heart of GIA's 'Excellent' grade.

But that's not to say that other proportions won't work - it's just that they are more difficult for the cutter to get to work.
It's like an 'optimisation' curve, with your shortlist of proportions being in the 'sweet spot'.
At the top of the curve (the sweet spot), small variations or rounding errors in proportions make little difference to performance. As you move away from the peak of the curve, small differences in proportions make a big difference to performance.

I am very curious how you come up with this? For those of us who like lots of dispersion the 53% tables should definitely be in this spread. It is the original table size that Tolkowsky suggested in his original description of the Ideal cut. Why do you dismiss it?

Wink

P.S. To soontomarry, it is this type of disagreement between posters that shores up the absolute necessity for you to see many diamonds and quality of cuts and decide which of them appeal the most to YOUR eyes.

What is meant of dispersion in lower table values like 53 and 54%?

Dispersion is visible in most diamonds, but diamonds with smaller tables will often show more of it.

Let's have a brief discussion of dispersion.

Dispersion is the play of colors that we often see in a diamond when a ray of light is bent sufficiently to display the rainbow colors to us that make up each ray of "white" light. Think back to your childhood and the prisms we played with as children. (If you are old enough, some of you younger pricescopers were deprived of such things and only played with cartoons, sigh.)

I have enclosed a picture of a prism and its affect on light below.

When the flash of color is wider than the pupil of the eye, it will be seen as colored light, or dispersion. When it is observed at a point where it is smaller than the pupil of the eye, it will be perceived of as white light since all of the colors are present at one time and are thus reconstituted into white light by the eye. By the way, this holds true for cameras too.

When the tables are smaller, there is a tendency for the dispersive rays to be smaller if the pavilion is cut properly too, and thus you will perceive more dispersion.

This is horribly simplified but it should give you the basis for the conversation.

Wink

P.S. There is a much more in depth discussion of this topic here.

 

[Chase035]

Thanks Wink.

 

[Karl_K]

smaller tables change the size location and shape of virtual facets which changes the character of the diamond.
In an RB the smaller table creates more med. size virtual facets increasing dispersion vs large(directional) and small(only effective in strong light) virtual facets.
Eventually you get to a point where you go to far. (around 50% unless you have an oec like pavilion)
What is interesting is many old diamonds had huge pavilion facets to gather light and high, small tabled crowns to break it up.
You would thing they would work against each other but they can balance each other out.

 

[Chase035]

How does star length and lower half affect this? For example, with a 54% table, what LH% and star lengths maximize dispersion without having too much of an effect on brilliance?

ex. I have a 54% table with a 75-76% LH and a 50-51% star length.

 

[stone-cold11]

Date: 2/28/2010 7:50:40 PM
Author: Chase035
How does star length and lower half affect this? For example, with a 54% table, what LH% and star lengths maximize dispersion without having too much of an effect on brilliance?

ex. I have a 54% table with a 75-76% LH and a 50-51% star length.

Take a look at the GOG August Vintage Rounds.

 

[Dreamer_D]

Date: 2/28/2010 11:18:20 AM
Author: ChunkyCushionLover

You would also be safest staying with the strict range of AGS0 cut grading because GIA Excellent is a much wider range, however the majority of posters prefer a more general approach listed below:

1) Put the numbers from the certificate including crown and pavilion angle, depth % and table% into HCA https://www.pricescope.com/cutadviser.asp it will tell you if the combination of crown and pavillion angles work well together.

2) All stones scoring under HCA <2. may be ideal cut diamonds with no leakage.

3) For any stones scoring HCA <2 check symmetry and leakage using an Idealscope http://www.ideal-scope.com/1.using_reference_chart.asp

I would edit this slightly for buying diamonds online:

1) Pick diamonds with AGS0 or GIA EX cut grades, or VG if it seems the symmetry or polish is what hurt the grade
2) Plug the numbers into the HCA, you want scores less than 2. Scores less than two are only okay *if* step 3 checks out.
3) If there is an IS available, then check it out, or request one. If it looks good that is really the best check you can accomplish online. The results of this step supercede the results of step 2.

If the IS is not available, but it passed 1 + 2, this may be enough for you to buy it online depending on your tolerance for deviations from "perfection".

 

[ChunkyCushionLover]

Date: 2/28/2010 8:43:04 PM
Author: dreamer_dachsie

Date: 2/28/2010 11:18:20 AM
Author: ChunkyCushionLover

You would also be safest staying with the strict range of AGS0 cut grading because GIA Excellent is a much wider range, however the majority of posters prefer a more general approach listed below:

1) Put the numbers from the certificate including crown and pavilion angle, depth % and table% into HCA https://www.pricescope.com/cutadviser.asp it will tell you if the combination of crown and pavillion angles work well together.

2) All stones scoring under HCA <2. may be ideal cut diamonds with no leakage.

3) For any stones scoring HCA <2 check symmetry and leakage using an Idealscope http://www.ideal-scope.com/1.using_reference_chart.asp

I would edit this slightly for buying diamonds online:

1) Pick diamonds with AGS0 or GIA EX cut grades, or VG if it seems the symmetry or polish is what hurt the grade
2) Plug the numbers into the HCA, you want scores less than 2. Scores less than two are only okay *if* step 3 checks out.
3) If there is an IS available, then check it out, or request one. If it looks good that is really the best check you can accomplish online. The results of this step supercede the results of step 2.

If the IS is not available, but it passed 1 + 2, this may be enough for you to buy it online depending on your tolerance for deviations from ''perfection''.

Sounds good to me a little clearer on the steps.

 

[Dreamer_D]

Date: 2/28/2010 9:38:00 PM
Author: ChunkyCushionLover

Date: 2/28/2010 8:43:04 PM
Author: dreamer_dachsie

Date: 2/28/2010 11:18:20 AM
Author: ChunkyCushionLover

You would also be safest staying with the strict range of AGS0 cut grading because GIA Excellent is a much wider range, however the majority of posters prefer a more general approach listed below:

1) Put the numbers from the certificate including crown and pavilion angle, depth % and table% into HCA https://www.pricescope.com/cutadviser.asp it will tell you if the combination of crown and pavillion angles work well together.

2) All stones scoring under HCA <2. may be ideal cut diamonds with no leakage.

3) For any stones scoring HCA <2 check symmetry and leakage using an Idealscope http://www.ideal-scope.com/1.using_reference_chart.asp

I would edit this slightly for buying diamonds online:

1) Pick diamonds with AGS0 or GIA EX cut grades, or VG if it seems the symmetry or polish is what hurt the grade
2) Plug the numbers into the HCA, you want scores less than 2. Scores greater than two are only okay *if* step 3 checks out.
3) If there is an IS available, then check it out, or request one. If it looks good that is really the best check you can accomplish online. The results of this step supercede the results of step 2.

If the IS is not available, but it passed 1 + 2, this may be enough for you to buy it online depending on your tolerance for deviations from ''perfection''.

Sounds good to me a little clearer on the steps.

GAH but I found a typo... I corrected it in the quote above. Meant to say in step 2 that Scores greater than two are only okay if step 3 checks out.

 

[Karl_K]

Date: 2/28/2010 7:50:40 PM
Author: Chase035
How does star length and lower half affect this? For example, with a 54% table, what LH% and star lengths maximize dispersion without having too much of an effect on brilliance?


ex. I have a 54% table with a 75-76% LH and a 50-51% star length.

depends on the c/p angle what minors are best with a smaller table.

 

[Dancing Fire]

Date: 2/28/2010 1:13:59 PM
Author: Wink

Date: 2/28/2010 10:42:15 AM
Author: FB.

I think that perhaps your table % is slightly small - the optimum is more like 55-57%.

Otherwise, your proportion shortlist is good and pretty safe.

GIA''s top grade is rather wide-ranging. Most on here would argue that GIA should have a grade above ''Excellent'' - perhaps called ''Ideal'' - which would include proportions in the heart of GIA''s ''Excellent'' grade.

But that''s not to say that other proportions won''t work - it''s just that they are more difficult for the cutter to get to work.
It''s like an ''optimisation'' curve, with your shortlist of proportions being in the ''sweet spot''.
At the top of the curve (the sweet spot), small variations or rounding errors in proportions make little difference to performance. As you move away from the peak of the curve, small differences in proportions make a big difference to performance.

I am very curious how you come up with this? For those of us who like lots of dispersion the 53% tables should definitely be in this spread. It is the original table size that Tolkowsky suggested in his original description of the Ideal cut. Why do you dismiss it?

Wink

P.S. To soontomarry, it is this type of disagreement between posters that shores up the absolute necessity for you to see many diamonds and quality of cuts and decide which of them appeal the most to YOUR eyes.

i like mine in the 53-55% range with a high crown.

 

[Chase035]

Say for 34.5/40.8 with those specs (54%, 75% LH, 50% star). I guess I want to understand how this works more so than an answer for those particular specs, but yes, that''s the stone I bought.