Why depth is not the opposite of spread in a fancy shape?

[whatmeworry]

Garry,
I don''t have an answer. It''s a hard task if not impossible. My understanding is that pricing of cuts to some extent depends on the yield from the rough, time spent cutting, exclusivity, branding, popularity. The first 2 factors you can take into account.
That does look like a deep pavilion but is it a weight saving measure or something that''s fundamental to its look?
I don''t know what they will ask for one of those but I bet it will be more than the price of a branded hearts and arrow.

 

[Garry H (Cut Nut)]

Date: 4/3/2010 6:41:31 PM
Author: whatmeworry
Garry,
I don''t have an answer. It''s a hard task if not impossible.

So you see it is best to proceed on the course we (the Cut Group) have initiated via DiamCalc and worry more about refinements much later

Re the Antwerp Twins - I do not care a lot about their success or failure in the marketplace as much as I care about making a playing field where they or anyone else can bring a product to the market and we (retailers) and you (consumers) can decide if we want them based on predicatable and transparent common information.

Date: 4/3/2010 6:41:31 PM
Author: whatmeworry
Garry,
My understanding is that pricing of cuts to some extent depends on the yield from the rough, time spent cutting, exclusivity, branding, popularity. The first 2 factors you can take into account.

Pricing is always what you can get from one side, and what I will pay for what you have on the other.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX deleted analogy based on prostitution.

 

[ChunkyCushionLover]

Date: 4/4/2010 6:17:02 AM
Author: Garry H (Cut Nut)

Date: 4/3/2010 6:41:31 PM
Author: whatmeworry
Garry,
I don''t have an answer. It''s a hard task if not impossible.

So you see it is best to proceed on the course we (the Cut Group) have initiated via DiamCalc and worry more about refinements much later

Re the Antwerp Twins - I do not care a lot about their success or failure in the marketplace as much as I care about making a playing field where they or anyone else can bring a product to the market and we (retailers) and you (consumers) can decide if we want them based on predicatable and transparent common information.

Date: 4/3/2010 6:41:31 PM
Author: whatmeworry
Garry,
My understanding is that pricing of cuts to some extent depends on the yield from the rough, time spent cutting, exclusivity, branding, popularity. The first 2 factors you can take into account.

Pricing is always what you can get from one side, and what I will pay for what you have on the other.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX deleted analogy based on prostitution.

AMEN

 

[Paul-Antwerp]

Date: 4/3/2010 1:14:47 AM
Author: Serg
re:Yes I read this link before, except that what is the diameter in a Fancy Cut Diamond? What I want is the surface area of the girdle plain.

this link has two definitions . one for OctoNus spread, other for AGS spread

OctoNus spread does not use diameter, we use only surface area

AGS uses diameter and it is work only for Round cuts

This is far off-topic, but definitely something that caught my attention.

On the first page of this thread, Garry Holloway of The Cut Group says the following:

"
The image below shows an extreme example of two ovals, one cushionish, where the table and depth % are the same.
Same LXW, same gidrdle thickness, but look at the two weights and spread data in the lower right of each DiamCalc window.
AGS also adopted this spread approach that we developed for DiamCalc.
"

Then, we here have Sergey Sivovolenko of The Cut Group saying:

"
this link has two definitions . one for OctoNus spread, other for AGS spread

OctoNus spread does not use diameter, we use only surface area

AGS uses diameter and it is work only for Round cuts
"

A very weird contradiction, I would say.

Live long,

 

[Garry H (Cut Nut)]

Date: 4/5/2010 6:56:41 AM
Author: Paul-Antwerp

Date: 4/3/2010 1:14:47 AM
Author: Serg
re:Yes I read this link before, except that what is the diameter in a Fancy Cut Diamond? What I want is the surface area of the girdle plain.

this link has two definitions . one for OctoNus spread, other for AGS spread

OctoNus spread does not use diameter, we use only surface area

AGS uses diameter and it is work only for Round cuts

This is far off-topic, but definitely something that caught my attention.

On the first page of this thread, Garry Holloway of The Cut Group says the following:

'
The image below shows an extreme example of two ovals, one cushionish, where the table and depth % are the same.
Same LXW, same gidrdle thickness, but look at the two weights and spread data in the lower right of each DiamCalc window.


AGS also adopted this spread approach that we developed for DiamCalc.
'

Then, we here have Sergey Sivovolenkodocume~1/garry~1.del/locals~1/temp/__skypeietoolbar_cache/e70d95847a8f5723cfca6b3fd9946506/session/gif/offline.gif)! important" skypename="sivovolenko"> docume~1/garry~1.del/locals~1/temp/__skypeietoolbar_cache/e70d95847a8f5723cfca6b3fd9946506/session/gif/arrow.gif)! important" skypename="sivovolenko"> of The Cut Group saying:

'
this link has two definitions . one for OctoNus spread, other for AGS spread

OctoNus spread does not use diameter, we use only surface area

AGS uses diameter and it is work only for Round cuts
'

A very weird contradiction, I would say.

Live long,

Paul Sergey is pointing out that AGS uses rounds by comparison to rounds only.

Sergey missed that AGS also does a spread penalty based on surface area for princess cuts, but in this case they chose to compare princess cuts with other princess cuts (which we believe is a mistake).

Paul do you know if AGS have algoriths to calculate spread or penalty's for emerald cuts and ovals?
(Edited to add, why do you think this is off-topic?)

 

[Karl_K]

Date: 4/5/2010 8:17:56 AM
Author: Garry H (Cut Nut)
Paul do you know if AGS have algoriths to calculate spread or penalty''s for emerald cuts and ovals?

Yes they do
SE is between -26% and -27% DC spread to drop down to 1.
I don''t know what it is for EC and ovals but there is one.

 

[Serg]

Octonus introduces Spread calculations in DC for any cut early than ASG did it even for round cut.
difference between OctoNus and ASG spread for round cut with ideal round girdle is minor ( minor shift)

So one person has rights to Say "AGS adopted OctoNus spread", but other person( who did not check history and calculations in details) can find here something contradictive
results are often depend from intentions

 

[Serg]

re:Sergey missed that AGS also does a spread penalty based on surface area for princess cuts, but in this case they chose to compare princess cuts with other princess cuts (which we believe is a mistake).

Garry, Why do you think I missed it? Please explain

We added ASG spread for RBC, because cutters asked us to do it( they need it during allocation and polishing to receive AGS0)
But cutters did not asked us( never) to add ASG spread for other cuts. And I am very very happy what they did not ask because I do not like add so misleading information.
may be a soon we will remove even ASG spread for RBC. ASG grade is not more important for our clients as it was several years ago

 

[Serg]

Date: 4/5/2010 6:56:41 AM
Author: Paul-Antwerp

Date: 4/3/2010 1:14:47 AM

Author: Serg

re:Yes I read this link before, except that what is the diameter in a Fancy Cut Diamond? What I want is the surface area of the girdle plain.


this link has two definitions . one for OctoNus spread, other for AGS spread


OctoNus spread does not use diameter, we use only surface area


AGS uses diameter and it is work only for Round cuts

This is far off-topic, but definitely something that caught my attention.


On the first page of this thread, Garry Holloway of The Cut Group says the following:


''

The image below shows an extreme example of two ovals, one cushionish, where the table and depth % are the same.

Same LXW, same gidrdle thickness, but look at the two weights and spread data in the lower right of each DiamCalc window.

AGS also adopted this spread approach that we developed for DiamCalc.

''


Then, we here have Sergey Sivovolenko of The Cut Group saying:


''

this link has two definitions . one for OctoNus spread, other for AGS spread

OctoNus spread does not use diameter, we use only surface area

AGS uses diameter and it is work only for Round cuts

''


A very weird contradiction, I would say.


Live long,

re:his is far off-topic,

I am strongly disagree with this statement.
Topic is about correlation between spread and depth. so spread definition is very important for this discussion . So CCL has full rights to ask it and I have full rights to give answer

it is unpleasant to see such attempts to control discussion and information

 

[Karl_K]

Date: 4/5/2010 1:16:29 PM
Author: Karl_K

Date: 4/5/2010 8:17:56 AM

Author: Garry H (Cut Nut)

Paul do you know if AGS have algoriths to calculate spread or penalty's for emerald cuts and ovals?

Yes they do

SE is between -26% and -27% DC spread to drop down to 1.

I don't know what it is for EC and ovals but there is one.

I wanted to clarify that that is the DC equivalent range to the AGS cut off for 0, I am not saying that they use the DC system to calculate it.

 

[ChunkyCushionLover]

Date: 4/5/2010 6:12:40 PM
Author: Serg

Date: 4/5/2010 6:56:41 AM
Author: Paul-Antwerp

Date: 4/3/2010 1:14:47 AM

Author: Serg

re:Yes I read this link before, except that what is the diameter in a Fancy Cut Diamond? What I want is the surface area of the girdle plain.


this link has two definitions . one for OctoNus spread, other for AGS spread


OctoNus spread does not use diameter, we use only surface area


AGS uses diameter and it is work only for Round cuts

This is far off-topic, but definitely something that caught my attention.


On the first page of this thread, Garry Holloway of The Cut Group says the following:


''

The image below shows an extreme example of two ovals, one cushionish, where the table and depth % are the same.

Same LXW, same gidrdle thickness, but look at the two weights and spread data in the lower right of each DiamCalc window.


AGS also adopted this spread approach that we developed for DiamCalc.

''


Then, we here have Sergey Sivovolenko of The Cut Group saying:


''

this link has two definitions . one for OctoNus spread, other for AGS spread

OctoNus spread does not use diameter, we use only surface area

AGS uses diameter and it is work only for Round cuts

''


A very weird contradiction, I would say.


Live long,

re:his is far off-topic,

I am strongly disagree with this statement.
Topic is about correlation between spread and depth. so spread definition is very important for this discussion . So CCL has full rights to ask it and I have full rights to give answer

it is unpleasant to see such attempts to control discussion and information

The reason why I asked for it was I worked on a correlation between cushion faceup girdle plain surface area using

(LXW - corners) /carat weight

versus tolkoswky round faceup girdle plain size using

Pie*(Average Radius)Squared/carat weight.

My results indicated that for cushions which have only slight rounding of the corners most cushions cut today have only a 5 - 20% less spread than a tolkowsky round.
I read in another thread that Garry said it could be often -30% in spread and I couldn''t find any cushion that came close unless the corners were really rounded or the depth was greater than 70%. My problem was in estimating the deduction in the corners and it was done in a rough fashion so I want to know how accurate Diamcalc is in giving me the surface area.

Serg you never really answered me, nor Gary who said he didn''t know, I assume you calculate the area of a polygon or count normalized pixels (once you have projected the facets onto the L -W plain) but really I am just guessing. I am interested in the confidence limits of the calculations done by Diamcalc and the actual spread in mm squared for some of the fancy shapes. I don''t feel its a strange question or unrelated to this thread because in my mind comparing mm squared girdle plain faceup surface area is as good as anything else right now and is much better than just saying their is no way to make a comparison and that comparing depth % is meaningless.

I''ll leave the debate on side surface area and perceived surface spread for another discussion.

 

[Serg]

re:Serg you never really answered me, nor Gary who said he didn''t know, I assume you calculate the area of a polygon or count normalized pixels (once you have projected the facets onto the L -W plain) but really I am just guessing.

CCL, I gave you direct answer 2 days ago. "firstly we project all facets in to girdle plan, then sum areas of all facets. " what exactly is not clear here ?
I do not hide any information about spread and our calculation of spread. but if you ask me how we calculate area of polygons and sum it, your question is very strange for me. area of polygon is sum of are triangles. Each polygon could be present as set of triangles . Should I publish formula for triangle area ???

BTW. shape of corners is not most important factor for spread cushion cut. angles pavilion facets near girdle plan is very important for spread

 

[Serg]

CCl,
if you know OctoNus spread and mass for your diamond, you can easy recalculate OctoNus area for same diamond and check your calculations for area ( because for reference mass we use round cut with same mass, so you need just take round with (mass your diamond+spread) and check what diameter is for this round.

 

[ChunkyCushionLover]

Date: 4/6/2010 3:31:06 AM
Author: Serg
CCl,
if you know OctoNus spread and mass for your diamond, you can easy recalculate OctoNus area for same diamond and check your calculations for area ( because for reference mass we use round cut with same mass, so you need just take round with (mass your diamond+spread) and check what diameter is for this round.

Thanks that method will serve my purpose.

 

[Garry H (Cut Nut)]

Date: 3/26/2010 11:36:22 AM
Author:Paul-Antwerp
This subject is a side-topic that came up in this thread, and probably deserves its own thread.

My point is that one simply cannot say that a deeper fancy shape means that the stone has less spread. This is because of two reasons.

First, in many fancy shapes, there is the length-to-width-ratio. The depth is calculated on the basis of the smallest diameter, the width. So, two stones might have the same depth, but a L/W-ratio that is 15% different. (1.75 is almost 17% more than 1.50). So, the same depth could easily have a difference in spread of 15%.
Paul I wanted to make mention of this statement - I think it went to the keeper (a cricket saying). it is a very valid point, and we will add it into a re-write of the Spread tutorial page that came from this excellent thread.

Second, most fancy shapes do not have just one main crown and pavilion angle. Any stone with multiple crown- and pavilion-angles can hide weight without affecting the spread. We should name this - it is called BULGE I have written articles about this effect in the PS-journal on princess-cuts, but it is even more obvious in step-cuts. Again here, a conservative estimate is that the same depth can hide another 15% in weight in the bulge of the pavilion and the crown.

Taking both into consideration, it shows that two fancy shapes with the same depth-percentage can differ up to 30% in spread.

Considering that the difference between a depth of 60% and one of 78% is also 30%, how can one then use depth to say something about spread?

Live long,

This thread was needed Paul and should have helped many prosumers learn and aid newbies all the better. Thanks.
Are we done?
Unpin?

 

[Serg]

Date: 4/10/2010 6:20:05 AM
Author: Garry H (Cut Nut)

Date: 3/26/2010 11:36:22 AM
Author:Paul-Antwerp
This subject is a side-topic that came up in this thread, and probably deserves its own thread.

My point is that one simply cannot say that a deeper fancy shape means that the stone has less spread. This is because of two reasons.

First, in many fancy shapes, there is the length-to-width-ratio. The depth is calculated on the basis of the smallest diameter, the width. So, two stones might have the same depth, but a L/W-ratio that is 15% different. (1.75 is almost 17% more than 1.50). So, the same depth could easily have a difference in spread of 15%.
Paul I wanted to make mention of this statement - I think it went to the keeper (a cricket saying). it is a very valid point, and we will add it into a re-write of the Spread tutorial page that came from this excellent thread.

Second, most fancy shapes do not have just one main crown and pavilion angle. Any stone with multiple crown- and pavilion-angles can hide weight without affecting the spread. We should name this - it is called BULGE I have written articles about this effect in the PS-journal on princess-cuts, but it is even more obvious in step-cuts. Again here, a conservative estimate is that the same depth can hide another 15% in weight in the bulge of the pavilion and the crown.

Taking both into consideration, it shows that two fancy shapes with the same depth-percentage can differ up to 30% in spread.

Considering that the difference between a depth of 60% and one of 78% is also 30%, how can one then use depth to say something about spread?

Live long,

This thread was needed Paul and should have helped many prosumers learn and aid newbies all the better. Thanks.
Are we done?
Unpin?

Garry, it is wrong statement. if 17% difference in girdle ratio is main difference between two fancy cuts then difference in Spread can not be easily 15%.
for example for marquises with default DC parameters and ratio 2.00 and 2.34, spreads are 22% and 27%. Difference in spreads is 5% instead 15%.
.

 

[Paul-Antwerp]

Sergey,

Give it up. Your efforts to confuse the readers and to target all my statements are pathetic.

A princess-cut with a L/W of 1.15 compared to one of 1.00 has 15% more spread.
An emerald-cut with a L/W of 1.50 compared to one of 1.30 has more than 15% more spread.

My statement clearly says that a fancy cut CAN have 15% more spread without it affecting the depth-%, not that it always does.

You are sufficiently intelligent to know and understand. Your constant witchhunt against me however is not a good sign of intelligence, it does not become you.

Live long,

 

[Serg]

Date: 4/11/2010 9:19:05 AM
Author: Paul-Antwerp
Sergey,

Give it up. Your efforts to confuse the readers and to target all my statements are pathetic.

A princess-cut with a L/W of 1.15 compared to one of 1.00 has 15% more spread.
An emerald-cut with a L/W of 1.50 compared to one of 1.30 has more than 15% more spread.

My statement clearly says that a fancy cut CAN have 15% more spread without it affecting the depth-%, not that it always does.

You are sufficiently intelligent to know and understand. Your constant witchhunt against me however is not a good sign of intelligence, it does not become you.

Live long,

there are 4 wrong statements in new Paul post.

See details fro Princess cut example in DC screenshots.

L/W 1.00 and 1.15 ( +15%), area is +15% of course too, but mass is bigger on +17% only( instead 23%)
so spread is bigger on 6% only instead 15% as in Paul statements.
My goal is to block confusing the readers from wrong posts and specially from PS tutorials . I even did not read Paul Post about 15% difference in spread before Garry decided to use it for PS tutorial

 

[Karl_K]

Defining spread as square mm per ct we find:

DC default 2 chevron princess
A 6x6 princess is 36square mm and 73.2% depth is 1.33ct
Now lets find the 1.15 diamond ratio with the same weight and depth.
It would be 5.7mm x 6.55mm for a surface area of 37.335

The surface area difference is 6.667%
So the 1.15 ratio with the same depth had a better spread of almost 7% with the same weight.

Defining spread as the longest side per ct then the difference is ~9%

I get what Serg is saying, Paul your right in concept but the relationship isn't linear.
Paul is right in the sense everything is never the same so 15% is possible but it isn't all a result of just the l/w ratio.
A 1.15 ratio CAN have 15% better spread with the same depth than a 1:1, it could also be 25% it can also have worse spread.
*shrug*

 

[Serg]

Date: 4/11/2010 2:34:22 PM
Author: Karl_K
Defining spread as square mm per ct we find:


DC default 2 chevron princess

A 6x6 princess is 36square mm and 73.2% depth is 1.33ct

Now lets find the 1.15 diamond ratio with the same weight and depth.

It would be 5.7mm x 6.55mm for a surface area of 37.335


The surface area difference is 6.667%

So the 1.15 ratio with the same depth had a better spread of almost 7% with the same weight.


Defining spread as the longest side per ct then the difference is ~9%


I get what Serg is saying, Paul your right in concept but the relationship isn't linear.

Paul is right in the sense everything is never the same so 15% is possible but it isn't all a result of just the l/w ratio.

A 1.15 ratio CAN have 15% better spread with the same depth than a 1:1, it could also be 25% it can also have worse spread.

*shrug*

Karl,
if we increase area on 15% we should increase mass on 23% to receive SAME spread( difference 0%)
so to receive difference in spread 15% when we change only L/W on 15% and "do not change " specially anything other( of course most angles become different) , we need receive weight increase on 8% only. It is not easy , it is very very difficult to receive such small mass increasing if you increase L/W on 15%. if you increase area in girdle plane on 15% by L/W, mass is bigger on similar %.

so concepts 1% in L/W gives near 1% in Spread is completely wrong.

see: I received 5%-6%( instead 15%) for marquise with L/W=2.00 and Princess with L/W=1.00

of course just depth does not enough to estimate Spread. there are a lot of reasons why depth has bad correlation with spread. Moon facets is most simplest example for consumers. but less spread doesn't mean worse cut performance . Moon facets are very helpful to increase cut performance .

 

[Serg]

Date: 4/11/2010 2:34:22 PM
Author: Karl_K
Defining spread as square mm per ct we find:


DC default 2 chevron princess

A 6x6 princess is 36square mm and 73.2% depth is 1.33ct

Now lets find the 1.15 diamond ratio with the same weight and depth.

It would be 5.7mm x 6.55mm for a surface area of 37.335


The surface area difference is 6.667%

So the 1.15 ratio with the same depth had a better spread of almost 7% with the same weight.


Defining spread as the longest side per ct then the difference is ~9%


I get what Serg is saying, Paul your right in concept but the relationship isn''t linear.

Paul is right in the sense everything is never the same so 15% is possible but it isn''t all a result of just the l/w ratio.

A 1.15 ratio CAN have 15% better spread with the same depth than a 1:1, it could also be 25% it can also have worse spread.

*shrug*

reefining spread as square mm per ct we find:

it cannot be Spread definition because such ratio is different for 1ct and 10ct diamonds (even if both have exactly same cut)

 

[Paul-Antwerp]

Gentlemen,

Why are you deliberately trying to distort my words?

Take two stones of the same weight, one with a L/W of 1.15, the other 1.00. Same depth-percentage.

Does one stone have 15% more spread than the other, yes or no? In a princess, yes, in an emerald, even more, in other shapes not necessarily.

You are trying to distort it by giving both stones the same proportions. That is misinformation to the extreme.

Live long,

 

[Serg]

Date: 4/12/2010 1:03:20 AM
Author: Paul-Antwerp
Gentlemen,

Why are you deliberately trying to distort my words?

Take two stones of the same weight, one with a L/W of 1.15, the other 1.00. Same depth-percentage.

Does one stone have 15% more spread than the other, yes or no? In a princess, yes, in an emerald, even more, in other shapes not necessarily.

You are trying to distort it by giving both stones the same proportions. That is misinformation to the extreme.

Live long,

Please read again first Paul post again:

"This subject is a side-topic that came up in this thread, and probably deserves its own thread.

My point is that one simply cannot say that a deeper fancy shape means that the stone has less spread. This is because of two reasons.

First, in many fancy shapes, there is the length-to-width-ratio. The depth is calculated on the basis of the smallest diameter, the width. So, two stones might have the same depth, but a L/W-ratio that is 15% different. (1.75 is almost 17% more than 1.50). So, the same depth could easilyhave a difference in spread of 15%.

Second, most fancy shapes do not have just one main crown and pavilion angle. Any stone with multiple crown- and pavilion-angles can hide weight without affecting the spread. I have written articles about this effect in the PS-journal on princess-cuts, but it is even more obvious in step-cuts. Again here, a conservative estimate is that the same depth can hide another 15% in weight in the bulge of the pavilion and the crown.

Taking both into consideration, it shows that two fancy shapes with the same depth-percentage can differ up to 30% in spread.

Considering that the difference between a depth of 60% and one of 78% is also 30%, how can one then use depth to say something about spread?

"
1)How did Paul receive 15% difference in spread in "First case"?
2)What is difference between "first Paul case" and "second Paul case" in first his post? where is this difference in last his post?
3) Did I distort any Paul statements ?

 

[Garry H (Cut Nut)]

Date: 3/26/2010 11:36:22 AM
Author:Paul-Antwerp
This subject is a side-topic that came up in this thread, and probably deserves its own thread.

My point is that one simply cannot say that a deeper fancy shape means that the stone has less spread. This is because of two reasons.

First, in many fancy shapes, there is the length-to-width-ratio. The depth is calculated on the basis of the smallest diameter, the width. So, two stones might have the same depth, but a L/W-ratio that is 15% different. (1.75 is almost 17% more than 1.50). So, the same depth could easily have a difference in spread of 15%.
Second, most fancy shapes do not have just one main crown and pavilion angle. Any stone with multiple crown- and pavilion-angles can hide weight without affecting the spread. I have written articles about this effect in the PS-journal on princess-cuts, but it is even more obvious in step-cuts. Again here, a conservative estimate is that the same depth can hide another 15% in weight in the bulge of the pavilion and the crown.

Taking both into consideration, it shows that two fancy shapes with the same depth-percentage can differ up to 30% in spread.

Considering that the difference between a depth of 60% and one of 78% is also 30%, how can one then use depth to say something about spread?

Live long,

For ease of reading - Pauls first post in its original formating, but with the relevant part in bold - Sergey has posted it above.
Paul Sergey has raised some relevant issues related to your topic
Why depth is not the opposite of spread in a fancy shape?

I am not sure how to incorporate it into the Tutorial so that it is both simple for newbies, and accurate.

Here is some relevant proposed text:
Fancy shapes have a much wider range of face-up spread than rounds. Depth % is poorly correlated to spread as a result of specific fancy cut designs. Popular fancy shapes that have a smaller spread than rounds are Princess, Asscher and Cushion cuts, whereas Oval, Marquise and Pear cuts often spread larger.

Some of the in-house fancy cut diamond cuts listed in the Pricescope database have quantitative spread comparisons to that of a standard Tolkowsky round brilliant. For example, a 1.00ct Princess cut that has a -15% spread has the same surface area as an 0.85ct round.

Moderation is usually key with fancy shape spread. A very shallow stone will have great spread, but may have durability and brilliance issues. Excessive depth or pavilion bulge will have you paying for extra weight you won’t see face-up. Some fancy cuts require extra depth to optimize angles for better brilliance, fire, and scintillation.

There are a myriad of parameters that can make a beautiful fancy shape, so when you are comparing spread in fancies, remember that they are proportioned differently than round brilliants. Their spread factors are often a result of specific design and each stone should be evaluated for its particular merits.

Any suggestions to incorporate ''bugle'' are welcome. Perhaps this image could do it?

 

[Serg]

reopular fancy shapes that have a smaller spread than rounds are Princess, Asscher and Cushion cuts, whereas Oval, Marquise and Pear cuts often spread larger.

Garry, I suppose to add : Diamonds with bigger L/W usually have bigger spread if we compare spread for same cut type.

 

[ChunkyCushionLover]

Date: 4/12/2010 4:34:17 AM
Author: Garry H (Cut Nut)

Date: 3/26/2010 11:36:22 AM
Author:Paul-Antwerp
This subject is a side-topic that came up in this thread, and probably deserves its own thread.

My point is that one simply cannot say that a deeper fancy shape means that the stone has less spread. This is because of two reasons.

First, in many fancy shapes, there is the length-to-width-ratio. The depth is calculated on the basis of the smallest diameter, the width. So, two stones might have the same depth, but a L/W-ratio that is 15% different. (1.75 is almost 17% more than 1.50). So, the same depth could easily have a difference in spread of 15%.
Second, most fancy shapes do not have just one main crown and pavilion angle. Any stone with multiple crown- and pavilion-angles can hide weight without affecting the spread. I have written articles about this effect in the PS-journal on princess-cuts, but it is even more obvious in step-cuts. Again here, a conservative estimate is that the same depth can hide another 15% in weight in the bulge of the pavilion and the crown.

Taking both into consideration, it shows that two fancy shapes with the same depth-percentage can differ up to 30% in spread.

Considering that the difference between a depth of 60% and one of 78% is also 30%, how can one then use depth to say something about spread?

Live long,

For ease of reading - Pauls first post in its original formating, but with the relevant part in bold - Sergey has posted it above.
Paul Sergey has raised some relevant issues related to your topic
Why depth is not the opposite of spread in a fancy shape?

I am not sure how to incorporate it into the Tutorial so that it is both simple for newbies, and accurate.

Here is some relevant proposed text:
Fancy shapes have a much wider range of face-up spread than rounds. Depth % is poorly correlated to spread as a result of specific fancy cut designs. Popular fancy shapes that have a smaller spread than rounds are Princess, Asscher and Cushion cuts, whereas Oval, Marquise and Pear cuts often spread larger.

Some of the in-house fancy cut diamond cuts listed in the Pricescope database have quantitative spread comparisons to that of a standard Tolkowsky round brilliant. For example, a 1.00ct Princess cut that has a -15% spread has the same surface area as an 0.85ct round.

Moderation is usually key with fancy shape spread. A very shallow stone will have great spread, but may have durability and brilliance issues. Excessive depth or pavilion bulge will have you paying for extra weight you won’t see face-up. Some fancy cuts require extra depth to optimize angles for better brilliance, fire, and scintillation.

There are a myriad of parameters that can make a beautiful fancy shape, so when you are comparing spread in fancies, remember that they are proportioned differently than round brilliants. Their spread factors are often a result of specific design and each stone should be evaluated for its particular merits.

Any suggestions to incorporate ''bugle'' are welcome. Perhaps this image could do it?

That sentence is incorrect as spread/carat weight is not linear.
A 1 carat princess would have a girdle plain surface area of 15% less than a Tolk Round, but a 0.85ct Tolk round would have a greater surface area than this princess.

 

[Serg]

CCL, Garry


there are two correct sentences for Garry example:

"Some of the in-house fancy cut diamond cuts listed in the Pricescope database have quantitative spread comparisons to that of a standard Tolkowsky round brilliant. For example, a 1.00ct Princess cut that has a -0.13ct spread has the same surface area as an 0.87ct round."

or

''Some of the in-house fancy cut diamond cuts listed in the Pricescope database have quantitative spread comparisons to that of a standard Tolkowsky round brilliant. For example, a 1.00ct Princess cut that has a -15% spread has the same surface area as an 0.87ct round. "

15%*0.87ct=0.13ct

 

[ChunkyCushionLover]

Date: 4/12/2010 10:40:28 AM
Author: Serg
CCL, Garry


there are two correct sentences for Garry example:

''Some of the in-house fancy cut diamond cuts listed in the Pricescope database have quantitative spread comparisons to that of a standard Tolkowsky round brilliant. For example, a 1.00ct Princess cut that has a -0.13ct spread has the same surface area as an 0.87ct round.''

or

''Some of the in-house fancy cut diamond cuts listed in the Pricescope database have quantitative spread comparisons to that of a standard Tolkowsky round brilliant. For example, a 1.00ct Princess cut that has a -15% spread has the same surface area as an 0.87ct round. ''

15%*0.87ct=0.13ct

Serg,

Statement one is only useful in describing the information used by Diamcalc users. There is no way to calculate carat weight spread relative to Tolk Round (Octonus Spread) using information from a certificate without using Diamcalc and I''ve never seen it available outside of the output of the program.

Statement two could be correct and useful if the definition of spread was clearly defined.

What is the definition of faceup spread for the tutorial?

I am still unclear why the pavillion angles and the trace of all facets onto the XY plain (girdle plain) should change the surface area.

In a perfect square shape the surface area of this plain is LxW, and the projection of all facets onto this plain and a sum should lead to exactly that area no matter what the pavillion looks like or the crown. The carat weight could change dramatically due to the facet design but the surface area of this plain if the Length and Width are held constant should not change.

If I am wrong please explain further.

 

[Karl_K]

Date: 4/12/2010 1:03:20 AM
Author: Paul-Antwerp
Gentlemen,


Why are you deliberately trying to distort my words?


Take two stones of the same weight, one with a L/W of 1.15, the other 1.00. Same depth-percentage.


Does one stone have 15% more spread than the other, yes or no? In a princess, yes, in an emerald, even more, in other shapes not necessarily.


You are trying to distort it by giving both stones the same proportions. That is misinformation to the extreme.


Live long,

Paul I am not distorting your words I just don''t see how the above is correct.

To say stone a at 1:15 l/w has 15% more spread than stone B at 1:1 l/w with the same depth and weight is just not always true.
It CAN be but its not even likely to be exactly 15%

 

[oldminer]

A Rectangular stone which measures 1:1.15 l/w has 15% more spread than an identical weight, and identical width SQUARE diamond which measures only 1:1 l/w. It would a matter of bulge, depth or both combined.

The same would not be true for pear, marq, oval, but only for rectangular shaped diamonds. These rounded configurations have variable outline curves and do not have spread based simply on length and width measures. It will have to be pixel counts of the girdle plane area or some other strategy to measure this area.