How important are HCA factor grades in assessing diamonds?

[stone-cold11]

Re: How important are HCA factor grades in assessing diamond

John- your explanation makes all the sense in the world- and if we look at diamonds in bulk, it likely explains a lot of the poorly cut stones out there- and we all agree there are plenty. But the generalization seems not to work in all cases.
Back to weight retention and, the question of if the 4.36ct was too deep- a question to Garry and John ( again)
If there's extra weight on this stone, how does it manifest itself?
That is to say, given that there's sufficient crown and pavilion angle, and more than ample spread ( in fact excellent spread for the weight)- where is this extra weight?
How much should the diamond have weighed?

I have explained previously in another discussion we had. There is a simple, approximate hand calculation using high sch math. Those with DiamCalc will probably be able to generate one with better accuracy.

Using the parameters from this chart.

Your Example stone,
Stone A. Table 60, Crown 32.0, Pavilion 41.8.

Stone situated in the center of GIA Ex cut for 60% table,
Stone B. Table 60, Crown 32.5, Pavilion 41.2.

To simplify calculation, assuming the diamond is made up of conical shapes, no faceting, volume, V = 1/3 Pi R^2 H,

where, Pi = 3.142, R = base radius of cone, H = height of cone.

Volume of a cylinder, used for the girdle, = Pi R^2 H

This diamond is made up of the crown volume, pavilion volume and girdle volume.

The crown volume is obtained from the subtraction of 2 cones, the crown cone, everything above the crown, and the table cone, everything above the table.

Stone A
Crown cone.
Height of the crown cone = 50 * Tan(32) = 31.24
Volume of the crown cone = 1/3 Pi (50)^2 * 31.24 = 81795.21

Table cone
Height of the table cone = (60/2) * Tan(32) = 18.74
Volume of the table cone = 1/3 Pi (60/2)^2 * 18.74 = 17667.76

Pavilion Cone
Height of the pavilion cone = 50 * Tan(41.80) = 44.71
Volume of the pavilion cone = 1/3 Pi (50)^2 * 44.71 = 117037.83

Girdle
Volume of the girdle = Pi (50)^2 * 3 = 23561.95

Total volume of Stone A = 204727.22
Depth = 60.2%

Stone B
Crown cone.
Height of the crown cone = 50 * Tan(32.5) = 31.85
Volume of the crown cone = 1/3 Pi (50)^2 * 31.85 = 83392.30

Table cone
Height of the table cone = (60/2) * Tan(32.5) = 19.11
Volume of the table cone = 1/3 Pi (60/2)^2 * 19.11 = 18012.74

Pavilion Cone
Height of the pavilion cone = 50 * Tan(41.20) = 43.77
Volume of the pavilion cone = 1/3 Pi (50)^2 * 43.77 = 114594.01

Girdle
Volume of the girdle = Pi (50)^2 * 3 = 23561.95

Total volume of Stone A = 203535.53
Depth = 59.5%

By Ratio, given original stone has a weight of 4.36carat, Stone B should weigh about
4.36/204727.22 * 203535.53 = 4.33carat, so about 0.03 carat.

The extra depth is where the weight comes from.
Depth of Stone A = 60.2%, Depth of Stone B = 59.5%.

If the limit is due to the crown height, meaning the crown angle is fixed at 32 degrees, if given a pavilion angle of 41.4, with a largish lower half, the carat weight will approximately come up to 4.32 carat with a depth of 59.5%.

 

[Garry H (Cut Nut)]

Re: How important are HCA factor grades in assessing diamond

However any system like this is only as good as the charts they look up. If I had been smart enough to commercialize mine I would do better charts knowing what I know and with the tools I have. But this is not easy work, and if or when I do it, I will do it well.

I'm trying to understand this: "However any system like this is only as good as the charts they look up. If I had been smart enough to commercialize mine I would do better charts knowing what I know and with the tools I have." I'm sorry if I'm dense, but can you elaborate?

The charts you can see at the link are data that I created using the best tools I had at the time.
I did this with lap top, glass of wine (or 2), sample stones from my stock and other suppliers, showing staff and customers for opinions, Ideal-scope and my versions of ASET using my old Firescope and a green fluoro bit of cardboard (which I also discovered late 1980's) and DiamCalc and this fire tool which only works on Explorer and is a lot of fun http://www.cutstudy.com/cut/english/comp/scint1.htm.

If I had 1% of the resources GIA (wasted) employed, I could do better charts today.
And i could do systems for some fancy shapes too - but that is hard because the data sets are much more complex. And because I know better approaches via my interactions with Serg and Yuri - it seems better to devise a far better approach that can work forwards to the creation of better looking stones.
Any venture capitalists interested?

 

[Garry H (Cut Nut)]

Re: How important are HCA factor grades in assessing diamond

Clearly a lot of the current style - which is trying to be "ideal cut" does follow the smaller table mantra.
Stones like the one I'm using for this example are very rare today.
The part about people preferring patterning after seeing it more- and the general issue of taste and what is new, or "old fashioned" was also interesting. The implication is younger observers will go for patterning in higher percentages than older observers.
What would you suppose the average age of the buyers of four carat diamonds?
IN my case, it's really not what I'm used to- I know what I like.
The contrast in this type of stone is more dispersed- this is elemental in the look.

Sergey has many times mentioned on this and earlier boards that larger stones should require deliberate special symmetry deviations - this inflamed the sensitivities of wink and other 8* fans at the time.

With regards to GIA "borrowing" your methodology: no question you published first- and probably did influence their work. ( they probably should have at least given you some credit)

I did recieve a personal apology from Al Gilbertson

John- your explanation makes all the sense in the world- and if we look at diamonds in bulk, it likely explains a lot of the poorly cut stones out there- and we all agree there are plenty. But the generalization seems not to work in all cases.
Back to weight retention and, the question of if the 4.36ct was too deep- a question to Garry and John ( again)
If there's extra weight on this stone, how does it manifest itself?
That is to say, given that there's sufficient crown and pavilion angle, and more than ample spread ( in fact excellent spread for the weight)- where is this extra weight?
How much should the diamond have weighed?

I think StoneCold answered the question with blinding unquestionable accuracy - the spread is great, but not greatest - and the stone lacks that sticking out of the setting effect (double D ) that i often call vertical spread

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

Thank you Stone!
I failed trig, but I'm sure your calculations may jibe.
.03ct.
That's .0068% waste- man, what a pig!

Seriously, you're totally proving my point.
If we're talking about three measly points on a 4.36carat stone, it's statistically insignificant.

We can apply this to John's statement over millions of carats- yet we need to balance that with Yoram's statement about "boutique" cutters.
This type of stone is exactly that type of stone.
They are NOT mass produced - simply due to rarity.

Yes Garry- do an HCA for fancies- that should keep it interesting here for a good long time

Seriously- how about looking at revisiting the charts for the HCA?
Also a different way to present results.
If the system was less linear at the top, it would be far less likely to be misunderstood. For example if stones below a certain threshold were termed , "worth further investigation" so folks would not make the easy assumption that a 1.5 is "better" than a stone scoring 2

Just a suggestion- you can tell me to go fly a kite.....( I still have not jumped in the lake like you asked a few years back

ETA- Garry we were posting at the same time.
Can you show me some examples from the PS DB of 4.36ct stones with greater spread than the one we're using for this discussion?
It might not have a high crown- but it will set very well in a ring- some people like a smoother, lower top to a ring- especially one this large.

 

[stone-cold11]

Re: How important are HCA factor grades in assessing diamond

So what is the selling price for that stone? Do a $/carat calculation and then tell me how much that 3 points mean in $? So I guess that translate to around 1k and buyers willing to buy that stone will not quibble over these chum change, but what does that mean to the cutter?

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

If we do a check of the PS database, stones in the same color clarity ( although none was triple ex) range in price, on a per carat basis from $23K and change to $29K and change per carat. From about $100k, up to $133517
That's a far greater difference than the $1000+- that .03ct represents.

The stone in discussion is no longer on our site.
1) it's the subject of this conversation
2) it's not available
3) there was a massive price error

 

[stone-cold11]

Re: How important are HCA factor grades in assessing diamond

If we do a check of the PS database, stones in the same color clarity ( although none was triple ex) range in price, on a per carat basis from $23K and change to $29K and change per carat. From about $100k, up to $133517
That's a far greater difference than the $1000+- that .03ct represents.

The stone in discussion is no longer on our site.
1) it's the subject of this conversation
2) it's not available
3) there was a massive price error

Not sure why you say that.

Even if we go by 29000/carat, that means it is $290 per point, so $1000 is at the high end estimation for a 3 points difference in weight for that size.

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

What I'm saying Stone is that there's as much as $33,000 difference in the price of stones with similar color clarity weight range and a large part of that price difference is due to cut- therefore the difference in our hypothetical example of saving .03ct ( $1000) is far less important than cutting a stone that will bring the highest price.
Basically, a 4.36ct triple EX is worth a lot more than a 4.39 VG.
It does happen to be worth $1000 more than a 4.33ct.
However I believe that if we're discussing the difference between $131,000 4.33ct, and $132,000 4.36ct there's many other obstacles this stone will need to overcome at the point of sale.
The greatest of which is that it needs to look very good to get someone to fork over that kind of money.

 

[John P]

Re: How important are HCA factor grades in assessing diamond

John- your explanation makes all the sense in the world- and if we look at diamonds in bulk, it likely explains a lot of the poorly cut stones out there- and we all agree there are plenty. But the generalization seems not to work in all cases.

Thank you. For the record both of the options I gave would be possible in any case: The second example would fit inside the outline for the actual diamond... In that second example table, crown height and girdle remain the same. To reach the center of GIA EX and improve the AGS grade to 0 the girdle diameter and pavilion depth (and logically the weight) would have been reduced.

Back to weight retention and, the question of if the 4.36ct was too deep- a question to Garry and John ( again)
If there's extra weight on this stone, how does it manifest itself?
That is to say, given that there's sufficient crown and pavilion angle, and more than ample spread ( in fact excellent spread for the weight)- where is this extra weight?
How much should the diamond have weighed?

I wouldn't say "should." I'm sure it finished as planned. But to answer your question; before posting the other day I calculated both options in wire-frame. Not knowing actual weight I used a 1 carat stone as the existing diamond (first image below).

As stated above, the second example fits inside the outline of the existing one; in fact it would be forced-to. Remember that when sawed conventionally, along the table facet, crown height down-to max possible girdle-diameter is a fixed number. In the 1 carat scenario that's 0.82 mm (seen in both images below). To get to the center of GIA EX (and earn AGS Ideal in the process) while keeping table size and crown height fixed, it would be necessary to cut a crown angle of 32.8 degrees, reducing the average girdle diameter by 3.3% (from 6.54 to 6.33mm). It would also be necessary to reduce the pavilion angle to the 41.2 required for that EX/Ideal grade.

The weight loss in this case is 10% (second image below). That would take a 4.36 carat stone down to 3.93 ct. I imagine everyone here will agree that the obvious choice with such a large piece of rough was to save 4 carats.

The fact that it's beautiful as-is is not being disputed. In planning I imagine all possible scenarios were considered. The way it was planned and executed was logical, and by staying over 4cts while getting inside the outer limit of EX it was also best for profitability.

Existing Diamond

Cut to center of EX/Ideal

 

[stone-cold11]

Re: How important are HCA factor grades in assessing diamond

What I'm saying Stone is that there's as much as $33,000 difference in the price of stones with similar color clarity weight range and a large part of that price difference is due to cut- therefore the difference in our hypothetical example of saving .03ct ( $1000) is far less important than cutting a stone that will bring the highest price.
Basically, a 4.36ct triple EX is worth a lot more than a 4.39 VG.
It does happen to be worth $1000 more than a 4.33ct.
However I believe that if we're discussing the difference between $131,000 4.33ct, and $132,000 4.36ct there's many other obstacles this stone will need to overcome at the point of sale.
The greatest of which is that it needs to look very good to get someone to fork over that kind of money.

I guess that prompted the cutter to shoot for the edge of the GIA Ex envelope instead of a safe point like what John pointed out? A mistake there would drop it to VG cut. Maybe it did and got polish off a little in the pavilion to get into the Ex.

 

[Garry H (Cut Nut)]

Re: How important are HCA factor grades in assessing diamond

John- your explanation makes all the sense in the world- and if we look at diamonds in bulk, it likely explains a lot of the poorly cut stones out there- and we all agree there are plenty. But the generalization seems not to work in all cases.

Thank you. For the record both of the options I gave would be possible in any case: The second example would fit inside the outline for the actual diamond... In that second example table, crown height and girdle remain the same. To reach the center of GIA EX and improve the AGS grade to 0 the girdle diameter and pavilion depth (and logically the weight) would have been reduced.

Back to weight retention and, the question of if the 4.36ct was too deep- a question to Garry and John ( again)
If there's extra weight on this stone, how does it manifest itself?
That is to say, given that there's sufficient crown and pavilion angle, and more than ample spread ( in fact excellent spread for the weight)- where is this extra weight?
How much should the diamond have weighed?

I wouldn't say "should." I'm sure it finished as planned. But to answer your question; before posting the other day I calculated both options in wire-frame. Not knowing actual weight I used a 1 carat stone as the existing diamond (first image below).

As stated above, the second example fits inside the outline of the existing one; in fact it would be forced-to. Remember that when sawed conventionally, along the table facet, crown height down-to max possible girdle-diameter is a fixed number. In the 1 carat scenario that's 0.82 mm (seen in both images below). To get to the center of GIA EX (and earn AGS Ideal in the process) while keeping table size and crown height fixed, it would be necessary to cut a crown angle of 32.8 degrees, reducing the average girdle diameter by 3.3% (from 6.54 to 6.33mm). It would also be necessary to reduce the pavilion angle to the 41.2 required for that EX/Ideal grade.

The weight loss in this case is 10% (second image below). That would take a 4.36 carat stone down to 3.93 ct. I imagine everyone here will agree that the obvious choice with such a large piece of rough was to save 4 carats.

The fact that it's beautiful as-is is not being disputed. In planning I imagine all possible scenarios were considered. The way it was planned and executed was logical, and by staying over 4cts while getting inside the outer limit of EX it was also best for profitability.

Existing Diamond

Cut to center of EX/Ideal

John I am willing to bet David or anyone else that the pavilion is shallower than 41.8 and probably could be even less than 41.6.
I also believe the stone has around 1 degree of crown and possibly a little pavilion painting.
David can you get the stone to Rhino, AGSL or GIA to take a Helium scan?

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

John- your explanation makes all the sense in the world- and if we look at diamonds in bulk, it likely explains a lot of the poorly cut stones out there- and we all agree there are plenty. But the generalization seems not to work in all cases.

Thank you. For the record both of the options I gave would be possible in any case: The second example would fit inside the outline for the actual diamond... In that second example table, crown height and girdle remain the same. To reach the center of GIA EX and improve the AGS grade to 0 the girdle diameter and pavilion depth (and logically the weight) would have been reduced.

Back to weight retention and, the question of if the 4.36ct was too deep- a question to Garry and John ( again)
If there's extra weight on this stone, how does it manifest itself?
That is to say, given that there's sufficient crown and pavilion angle, and more than ample spread ( in fact excellent spread for the weight)- where is this extra weight?
How much should the diamond have weighed?

I wouldn't say "should." I'm sure it finished as planned. But to answer your question; before posting the other day I calculated both options in wire-frame. Not knowing actual weight I used a 1 carat stone as the existing diamond (first image below).

As stated above, the second example fits inside the outline of the existing one; in fact it would be forced-to. Remember that when sawed conventionally, along the table facet, crown height down-to max possible girdle-diameter is a fixed number. In the 1 carat scenario that's 0.82 mm (seen in both images below). To get to the center of GIA EX (and earn AGS Ideal in the process) while keeping table size and crown height fixed, it would be necessary to cut a crown angle of 32.8 degrees, reducing the average girdle diameter by 3.3% (from 6.54 to 6.33mm). It would also be necessary to reduce the pavilion angle to the 41.2 required for that EX/Ideal grade.

The weight loss in this case is 10% (second image below). That would take a 4.36 carat stone down to 3.93 ct. I imagine everyone here will agree that the obvious choice with such a large piece of rough was to save 4 carats.

The fact that it's beautiful as-is is not being disputed. In planning I imagine all possible scenarios were considered. The way it was planned and executed was logical, and by staying over 4cts while getting inside the outer limit of EX it was also best for profitability.

Existing Diamond

Cut to center of EX/Ideal

Again thank you for the technical expertise John.
I do disagree with the part in bold.
Even if we forget about ccl's statements questioning the cutter's motivation behind the resultant stone, there's the HCA score.
This is certainly a discussion of how the HCA related to cut quality- easy to relate to a stone's beauty.
To his credit, Garry himself mentioned the HCA was too hard on this stone


Re the two examples you posted today- neither has the proportions of the stone in question ( the 60/60 in your wireframe had 44.7PA vs 41.8 for my example), so what is the relevance?

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

John- your explanation makes all the sense in the world- and if we look at diamonds in bulk, it likely explains a lot of the poorly cut stones out there- and we all agree there are plenty. But the generalization seems not to work in all cases.

Thank you. For the record both of the options I gave would be possible in any case: The second example would fit inside the outline for the actual diamond... In that second example table, crown height and girdle remain the same. To reach the center of GIA EX and improve the AGS grade to 0 the girdle diameter and pavilion depth (and logically the weight) would have been reduced.

Back to weight retention and, the question of if the 4.36ct was too deep- a question to Garry and John ( again)
If there's extra weight on this stone, how does it manifest itself?
That is to say, given that there's sufficient crown and pavilion angle, and more than ample spread ( in fact excellent spread for the weight)- where is this extra weight?
How much should the diamond have weighed?

I wouldn't say "should." I'm sure it finished as planned. But to answer your question; before posting the other day I calculated both options in wire-frame. Not knowing actual weight I used a 1 carat stone as the existing diamond (first image below).

As stated above, the second example fits inside the outline of the existing one; in fact it would be forced-to. Remember that when sawed conventionally, along the table facet, crown height down-to max possible girdle-diameter is a fixed number. In the 1 carat scenario that's 0.82 mm (seen in both images below). To get to the center of GIA EX (and earn AGS Ideal in the process) while keeping table size and crown height fixed, it would be necessary to cut a crown angle of 32.8 degrees, reducing the average girdle diameter by 3.3% (from 6.54 to 6.33mm). It would also be necessary to reduce the pavilion angle to the 41.2 required for that EX/Ideal grade.

The weight loss in this case is 10% (second image below). That would take a 4.36 carat stone down to 3.93 ct. I imagine everyone here will agree that the obvious choice with such a large piece of rough was to save 4 carats.

The fact that it's beautiful as-is is not being disputed. In planning I imagine all possible scenarios were considered. The way it was planned and executed was logical, and by staying over 4cts while getting inside the outer limit of EX it was also best for profitability.

Existing Diamond

Cut to center of EX/Ideal

John I am willing to bet David or anyone else that the pavilion is shallower than 41.8 and probably could be even less than 41.6.
I also believe the stone has around 1 degree of crown and possibly a little pavilion painting.
David can you get the stone to Rhino, AGSL or GIA to take a Helium scan?

Hi Garry- the stone is no longer available to be used for further examination.
Are you suggesting GIA made an error on the 41.8- or that GIA's method of averaging caused the alleged error?

 

[Garry H (Cut Nut)]

Re: How important are HCA factor grades in assessing diamond

Hi Garry- the stone is no longer available to be used for further examination.
Are you suggesting GIA made an error on the 41.8- or that GIA's method of averaging caused the alleged error?

Yes

 

[John P]

Re: How important are HCA factor grades in assessing diamond

The fact that it's beautiful as-is is not being disputed. In planning I imagine all possible scenarios were considered. The way it was planned and executed was logical, and by staying over 4cts while getting inside the outer limit of EX it was also best for profitability.

Again thank you for the technical expertise John.
I do disagree with the part in bold.
Even if we forget about ccl's statements questioning the cutter's motivation behind the resultant stone, there's the HCA score.
This is certainly a discussion of how the HCA related to cut quality- easy to relate to a stone's beauty.
To his credit, Garry himself mentioned the HCA was too hard on this stone.

I suppose the disconnect is the word beauty. As you like to say, people appreciate different things.

In any event, you're welcome. I enjoy the subject immensely. Rough-to-polished has so many possibilities. It would be great to see more creativity and optimization (and I'm not just talking about rounds - on the contrary). I hope to put up some amazing images from factories I visited in India last month...some huge, with vast outputs, and one small but amazingly progressive (eye-opening) boutique.

Re the two examples you posted today- neither has the proportions of the stone in question ( the 60/60 in your wireframe had 44.7PA vs 41.8 for my example), so what is the relevance?

Please look again? PA is 41.8. Pavilion depth is 44.7 (I have too much OCD to make that mistake)

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

John- how about we substitute "well cut" for "beauty"
With regards to the stone being well cut, HCA, as well as this discussion has called that into question.

I could easily read your response as an endorsement of the way this stone was cut- but I could also get the impression you would have rather seen it loose the hypothetical 10% ( you described this as "the obvious" choice).

My point here is that the second guessing of GIA is more about personal taste, as opposed to industry standards. Then we add the "science" and it's a lock- the implication ( actually stated directly) is that GIA declaration of a stone being "EX" cut grade can't be trusted.
Garry- while it's certainly possible GIA made an error on the PA, it's highly unlikely, especially considering the size and importance of the stone

 

[John P]

Re: How important are HCA factor grades in assessing diamond

John- how about we substitute "well cut" for "beauty"

Wait a minute. Aren't you the guy who always says "beauty" can be different from what some consider "well-cut?"

I could easily read your response as an endorsement of the way this stone was cut- but I could also get the impression you would have rather seen it loose the hypothetical 10% ( you described this as "the obvious" choice).

I don't recall saying that David. Is it possible you're mis-remembering the word "optimum"?

My point here is that the second guessing of GIA is more about personal taste, as opposed to industry standards. Then we add the "science" and it's a lock - the implication ( actually stated directly) is that GIA declaration of a stone being "EX" cut grade can't be trusted.

You trust it and that's cool. Others find its range too wide to trust it completely. Neither position is right or wrong; as long as you're buying the diamond for yourself, or showing it to a client who is using his/her own eyes you can decide what to trust for yourself, and so can your clients.

Factually, the introduction of GIA's cut grade for round brilliants in 2006 was one of the best things ever to happen in our industry. It has increased global consumer awareness of cut and factories have adapted cut quality upwards (in general). Many professionals put their faith in it. But even GIA folks will agree that the system was designed to serve a whole planet. It is not a niche system and may not cater to everyone with niche tastes. Considering the wide range permitted, nobody should be surprised that cut-focused pros and consumer enthusiasts may not approve of the entire span of the grade.

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

John- your explanation makes all the sense in the world- and if we look at diamonds in bulk, it likely explains a lot of the poorly cut stones out there- and we all agree there are plenty. But the generalization seems not to work in all cases.

Thank you. For the record both of the options I gave would be possible in any case: The second example would fit inside the outline for the actual diamond... In that second example table, crown height and girdle remain the same. To reach the center of GIA EX and improve the AGS grade to 0 the girdle diameter and pavilion depth (and logically the weight) would have been reduced.

Back to weight retention and, the question of if the 4.36ct was too deep- a question to Garry and John ( again)
If there's extra weight on this stone, how does it manifest itself?
That is to say, given that there's sufficient crown and pavilion angle, and more than ample spread ( in fact excellent spread for the weight)- where is this extra weight?
How much should the diamond have weighed?

I wouldn't say "should." I'm sure it finished as planned. But to answer your question; before posting the other day I calculated both options in wire-frame. Not knowing actual weight I used a 1 carat stone as the existing diamond (first image below).

As stated above, the second example fits inside the outline of the existing one; in fact it would be forced-to. Remember that when sawed conventionally, along the table facet, crown height down-to max possible girdle-diameter is a fixed number. In the 1 carat scenario that's 0.82 mm (seen in both images below). To get to the center of GIA EX (and earn AGS Ideal in the process) while keeping table size and crown height fixed, it would be necessary to cut a crown angle of 32.8 degrees, reducing the average girdle diameter by 3.3% (from 6.54 to 6.33mm). It would also be necessary to reduce the pavilion angle to the 41.2 required for that EX/Ideal grade.

The weight loss in this case is 10% (second image below). That would take a 4.36 carat stone down to 3.93 ct. I imagine everyone here will agree that the obvious choice with such a large piece of rough was to save 4 carats.

The fact that it's beautiful as-is is not being disputed. In planning I imagine all possible scenarios were considered. The way it was planned and executed was logical, and by staying over 4cts while getting inside the outer limit of EX it was also best for profitability.

Existing Diamond

Cut to center of EX/Ideal

John- I know I sometimes read quickly- and it's possible to miss things, but you did say obvious.

In terms of the concept of beauty- and the concept of well cut....
Yes, I do have considerations about how perception of beauty is sometimes overlooked in discussions here on PS- but in this specific case, we're discussing assessing cut quality.

I trust GIA a lot- that's true- however I would not buy a stone simply becasue GIA graded the cut EX.
That is to say, I also have preferences, and the grade does encompass a variety of different styles of round brilliant, not all of which are my personal preference.
As it happens, I found a stone that is not typical in today's market. I am crazy about, it is GIA EX cut grade- and scores poorly on HCA, making it an interesting test case.
This discussion has also called into question the motivation behind the decision to cut the stone this way.
My point is that the stones within GIA EX that John ( or anyone) might select might not be the one I would pick- but that does not mean that it's not well cut.
Just as I feel it's a mistake to eliminate stones based on where they sit within GIA EX, or by using HCA, I also believe that cut conscious consumers should indeed not assume they will love all stones GIA grades EX.
However it is safe to say that any stone receiving such grade is indeed well cut- and will be considered so by the trade at large. There's also no trade accepted discount for stones sitting at the outer edge of GIA's grade, as opposed to those smack in the middle. There may be a premium for stones that are cut to a certain tolerance and limited range of visuals- such as H&A or "boutique" brands of "super Ideal" cuts. This is more proprietary - associated with branding.

I'm not as much a fan of the AGS system as it does exclude stones that I would find to be more attractive than others which would be included in AGSL's top cut grade.

 

[ChunkyCushionLover]

Re: How important are HCA factor grades in assessing diamond

John Pollard - Thanks for debunking the theory that weight saving in planning only occurs at the carat and half carat mark.
These are your two theoretical stones in wireframe.


Looking at the wireframe any consumer can see the blue frame would be cheaper/carat to produce or have a higher finished weight.

Garry H - You are right, this stone can't even be modelled in Diamcalc without changing the crown height % and the girdle thicknesses.
Jp's example while close is no substitute for a scan. GIA's rounding of eight measurments and scan errors can change things a lot.
If RD hadn't removed the listing I would have tweaked it a little more with the correct star%.

RD - I am curious this a boutique house that offered this stone, do they have a wide selection of 60/60s? Do they share your beauty preference for assymetry and 60% table size enough to deliberately produce stones consistantly with this appearance?

 

[John P]

Re: How important are HCA factor grades in assessing diamond

John- I know I sometimes read quickly- and it's possible to miss things, but you did say obvious.

Ok. I found it David... And sorry to pick nits, but I think this matters.

You said:

...I could also get the impression you would have rather seen it loose the hypothetical 10% ( you described this as "the obvious" choice).

When actually I said the opposite:

...I imagine everyone here will agree that the obvious choice with such a large piece of rough was to save 4 carats.

You also believed my 60/60 calculations had not used a 41.8 PA - when they did (I wrote a polite correction earlier about my being OCD - not sure you saw it?)

The reason this matters is because I feel it's important to avoid unnecessary misunderstandings. Lately I am observing recurring context-miscues in threads which, in my opinion, interfere with productive discussion. I've lurked more than posted in recent history; partly because of the acrimony this brings. I cringe whenever a thread swerves from dialogue and dissolves into personal accusations about someone ignoring X, not understanding Y or failing to read Z. These are discussion-killers which foster resentment.

To be clear: While I'm using on-hand examples from my exchange with David my appeal is to everyone -myself included- hoping for more thorough reading, polite redirection (if necessary) and willingness to re-read (if necessary). In fact I re-read this thread three times to find where I used the word "obvious" - since I knew David felt strongly about it and truly wanted to clear up the misconception.

Common ground is critical for forward movement. David, I think we have plenty of common ground. And while not everything we discuss will stand in the same place it's nice to acknowledge fundamentals which do overlap, since divergent discussions can then have a chance for roots in the same place.

I apologize for the off-topic but believe this is worth mentioning considering recent policy discussions by the admin in the pinned thread.

David, I promise to reply on-topic later as time permits.

Cheers,

 

[risingsun]

Re: How important are HCA factor grades in assessing diamond

RD do you have a video of the diamond?

This is the stone.

http://rockdiamond.com/index.php/je...und-brilliant-h--vs1-gia-stunning-stone-r3558

The largish lgf results in not much leakage. Note that the stone is placed too deep into the ASET.

The link does not bring you to the stone

 

[stone-cold11]

Re: How important are HCA factor grades in assessing diamond

The link does not bring you to the stone

RD pull it off.

If we do a check of the PS database, stones in the same color clarity ( although none was triple ex) range in price, on a per carat basis from $23K and change to $29K and change per carat. From about $100k, up to $133517
That's a far greater difference than the $1000+- that .03ct represents.

The stone in discussion is no longer on our site.
1) it's the subject of this conversation
2) it's not available
3) there was a massive price error

EDT:
The video is still there, if it is not against PS policy. If it is, the mods might take it off but you can search youtube for RD's website and find the 60/60 crushedice.

http://www.youtube.com/user/diamondsbylauren#p/u/34/iThUVa5ND6Q

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

John- we are so on the same page regarding fine tuning the discussions to avoid acrimony.
I apologize for misreading the PA- I did see the correction- in light of your salient comments, I should have noted that.
Also see your point about the "obvious choice"- which I took to imply something other than what you meant to put out there.
Even that statement, to me, seems to position the resultant stone as a compromise to save weight, when I don't feel that's the case any more than any diamond is a compromise- but I I know you'll add more content soon.

I also agree that we share far more common ground than disagreements over a wide range of issues

Marian, I removed the stone from our site to allow an open discussion, while respecting PS rules.

I can post photos, and link to the video ( if that is ok)

CCL- the house that cut this stone specializes in Fancy Colors- and is a very important player on the world stage in that area.
They obtained a few very large pieces of colorless rough- which they have marketed in a different manner than the large companies ( and boutique houses) normally cutting this type of stone.

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

The link does not bring you to the stone

RD pull it off.

If we do a check of the PS database, stones in the same color clarity ( although none was triple ex) range in price, on a per carat basis from $23K and change to $29K and change per carat. From about $100k, up to $133517
That's a far greater difference than the $1000+- that .03ct represents.

The stone in discussion is no longer on our site.
1) it's the subject of this conversation
2) it's not available
3) there was a massive price error

EDT:
The video is still there, if it is not against PS policy. If it is, the mods might take it off but you can search youtube for RD's website and find the 60/60 crushedice.

http://www.youtube.com/user/diamondsbylauren#p/u/34/iThUVa5ND6Q

Thanks Stone!

in fact, I was struck by how the lack of patterning on this stone reminded me somewhat of crushed ice, in a round diamond

 

[stone-cold11]

Re: How important are HCA factor grades in assessing diamond

There is patterning, just no/not significant contrast. The largish lower halves are the ones giving it a splintery look that with slight tilt results in crush ice.

I think that is why you do not like the tolk proportions, the contrast.

 

[ChunkyCushionLover]

Re: How important are HCA factor grades in assessing diamond

CCL- the house that cut this stone specializes in Fancy Colors- and is a very important player on the world stage in that area.
They obtained a few very large pieces of colorless rough- which they have marketed in a different manner than the large companies ( and boutique houses) normally cutting this type of stone.

What does that mean marketed in a different manner? I once again ask you if any other large pieces of rough were cut to 60T/60D CA32PA41.8 rounds like this one by them?

All due respect ccl- you have NO idea as to how or why the stone was cut as it was.

I find this statememnt rather acrimonious in nature and you haven't provide any support for your opinion even now.
If not for weight saving are you still claiming they deliberately chose assymetry, deep pavilion and smaller VFs because they deem it more beautiful like you?

Or will you accept the more plausible answer which was to keep it above 4 carats and maintain GIA excellent and trying to minnimize the tradeoff in brightness under the table with longer lower halves.

Why not ask maybe they have cutting notes on this one?

 

[risingsun]

Re: How important are HCA factor grades in assessing diamond

Thanks Stone, the link worked. David, is there are video for the diamond under discussion? If so, can you post a link to it.

Thanks!

 

[Rockdiamond]

Re: How important are HCA factor grades in assessing diamond

Marian,
the link Stone posted features the 60/60 under discussion here- as well as another stone with what I'm calling more distinct patterning.

In terms of contrast, versus patterning: Stone, the patterns this stone exhibited were extremely small in relation to the surface area.


ccl- there's no hard fast rule, but generally houses specializing in important colorless stones might very well follow a different line of reasoning in the cutting- as well as how they sell the stones. Different buyers might very well lead to different decsions in the cutting.
We did see a few other 60/60 +- stones from them.
None had this exact proportion set.

 

[ChunkyCushionLover]

Re: How important are HCA factor grades in assessing diamond

Marian,
the link Stone posted features the 60/60 under discussion here- as well as another stone with what I'm calling more distinct patterning.

In terms of contrast, versus patterning: Stone, the patterns this stone exhibited were extremely small in relation to the surface area.

ccl- there's no hard fast rule, but generally houses specializing in important colorless stones might very well follow a different line of reasoning in the cutting- as well as how they sell the stones. Different buyers might very well lead to different decsions in the cutting.
We did see a few other 60/60 +- stones from them.

RD,

I can see how you have chosen to try to sell it, you've made it clear several times in this thread and in the listing.

I am more interested in understanding how the cutting house chose to sell and market it to you could you please elaborate.
You said

which they have marketed in a different manner than the large companies

How was the appearance marketed to you?
Did you have any influence on their rough planning? (cut to your spec as you or your taste was the buyer?)

Did you even sell this stone?

 

[Lula]

Re: How important are HCA factor grades in assessing diamond

There is patterning, just no/not significant contrast. The largish lower halves are the ones giving it a splintery look that with slight tilt results in crush ice.

I think that is why you do not like the tolk proportions, the contrast.

I had the same thought, Stone.

RD, the video you linked is a great learning tool for newbies on what "contrast" is and how it affects the appearance of the stone. Interesting that both those stones are 60/60 cuts. The lgf's on the H&A stone are very short compared to the lgfs of the other stone. There is a lot of contrast in that H&A stone. The stone on the left, which you prefer has almost no contrast, to my eye. This makes it look very bright, but quite flat (to my eye). My eye is also drawn to the large white circle in the center of the stone (table reflection?) and this is what I -- personal preference disclaimer! -- really dislike about these particular cut parameters.

But someone else may love the look.

And I don't have any problem with someone preferring the look of a splintery 60/60 (like the stone on the left in the video) or any well-cut 60/60 over a Tolk. What I have a problem with is vendors -- online or B&M -- not educating their customers on the differences. I think this thread has gone a long ways toward providing that education. And it really helps to see the stones in photos and videos, so I thank RD for posting the stone and I thank the mods for the recent change allowing these sorts of photos/videos.

A Tolk, and the two 60/60s in RD's video will perform very differently in real life and under different lighting conditions. I'm not always sure consumers know what those differences are enough to prefer one over the other without doing a fair amount of research/comparison.