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Can CUT be a graded on SIs

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DBM

Shiny_Rock
Joined
Oct 24, 2006
Messages
404
I''ve had this in my head for awhile:

Given that we have various parameters, proportions, ranges, percentages, etc for determing ideal criteria for an excellent CUT or light return (as some will equate the two). My issue is though as on SI diamonds the nature of the SI can greatly alter the light return of even the best proportioned diamond, especially in a case, for instance, where you have a cloud or carbon towards the bottom of the diamond which then causes its reflection in all facets of the diamond. The cut computations will give an EXCELLENT yield for light return when in fact the SI is "blocking" a significant amount of the reflection throughout the diamond.

Can you really calculate a CUT grade on SIs??
 

C Smith

Shiny_Rock
Joined
Jun 14, 2006
Messages
176
Sure you can run the numbers but it still comes down to the character of the stone to your own eye in differing light conditions. Sure, you can cut grade any diamond. Will every diamond meet your expectations because of it's good cut? Probably not. I've seen stones that look good on paper that just look lifeless. Many of those were SI's. Still, a poor cut will look poor most of the time regardles of clarity. Cut is still king I think with SI's.
 

Regular Guy

Ideal_Rock
Joined
Jul 6, 2004
Messages
5,951
Date: 11/23/2006 12:17:32 PM
Author:DBM

Can you really calculate a CUT grade on SIs??
I''m just a nosy bystander here, who has gotten sucked in for no good apparent reason.

I do appreciate your fresh questions.

As I read it, the question was looked at substantively, recently, here, and commented on by some experts on the forum. I think it''s a question of physics...as to what factors trump what factors. Right?

Though I don''t know that there''s been a measured correlation between the attempt to take direct measures of light performance, such as Dave does with his Imagem, and is done with Gemex. But, purportedly, these would record what your concerned about. Though Dave has encouraged use of his system by waving hands at the concerns you''re pointing out, I think he is only as restrained in the above as he might be. Paul, on the other hand, cuts diamonds, and would also be concerned about this. Moreover...AGS & GIA both seem contented to apply their systems...both fundamentally proportions based...to what would be, as you say, aka light behavior. Although it''s fair game to ask the question, I wonder if it hasn''t pretty effectively been answered.

Happy Thanksgiving!
 

DBM

Shiny_Rock
Joined
Oct 24, 2006
Messages
404
Date: 11/23/2006 12:47:01 PM
Author: Regular Guy

Date: 11/23/2006 12:17:32 PM
Author:DBM

Can you really calculate a CUT grade on SIs??
I''m just a nosy bystander here, who has gotten sucked in for no good apparent reason.

I do appreciate your fresh questions.

As I read it, the question was looked at substantively, recently, here, and commented on by some experts on the forum. I think it''s a question of physics...as to what factors trump what factors. Right?

Though I don''t know that there''s been a measured correlation between the attempt to take direct measures of light performance, such as Dave does with his Imagem, and is done with Gemex. But, purportedly, these would record what your concerned about. Though Dave has encouraged use of his system by waving hands at the concerns you''re pointing out, I think he is only as restrained in the above as he might be. Paul, on the other hand, cuts diamonds, and would also be concerned about this. Moreover...AGS & GIA both seem contented to apply their systems...both fundamentally proportions based...to what would be, as you say, aka light behavior. Although it''s fair game to ask the question, I wonder if it hasn''t pretty effectively been answered.

Happy Thanksgiving!
Ah excellent. thank you!
I''m still not fully familiar with ImaGem or GemEx so i''ll have to read up about those. thx. I don''t know if anyone mentioned the SIs that reflect throughout the facets though.
 

etienneperret

Rough_Rock
Joined
Oct 3, 2005
Messages
49
Cut, is the shape and proportions of a gemstone. In theory when the angles and proportions are optimized for the refractive index of the gemstone the stone will have the greatest brilliance. The size of an inclusion of an SI clarity stone is very minor, unless you have a tiny stone. I do not believe you need to worry about an SI inclusion affecting the brilliance of a diamond to any significant amount. Now an I3 clarity is another story, there the inclusions definitely will impact the light traveling through the diamond.
 

DBM

Shiny_Rock
Joined
Oct 24, 2006
Messages
404
Date: 11/23/2006 2:15:36 PM
Author: etienneperret
Cut, is the shape and proportions of a gemstone. In theory when the angles and proportions are optimized for the refractive index of the gemstone the stone will have the greatest brilliance. The size of an inclusion of an SI clarity stone is very minor, unless you have a tiny stone. I do not believe you need to worry about an SI inclusion affecting the brilliance of a diamond to any significant amount. Now an I3 clarity is another story, there the inclusions definitely will impact the light traveling through the diamond.
You''re right in many ways but i think it still will be an issue by: a. small stones b. inclusions that are not crystals or even feathers but clouds (especially clouds that get reflected througout the stone because they''re towards the bottom). clouds as inclusion in the wrong place can give the whole stone a "haze" if you will on it''s brilliance.
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
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Messages
14,600
Daniel in general clarity must be well below SI before there is a reduction in brilliance.

Except when , as you noted above, the inclusions are clouds.

Here is what GIA had to say:


And a little later they added this:

The Effect of Other Diamond Properties and
Conditions on Brightness and Fire. Our Brightness
and Fire teams evaluated the brightness and fire of
688 diamonds with a range of color, clarity, polish
and symmetry grades, girdle condition (bruted, polished,
or faceted), and blue fluorescence1 intensity
(from none to very strong), as given in the first column
of table 2. From these evaluations, we assessed
the interaction of these properties or conditions
with apparent brightness and fire (by comparing the
predicted metric values of these diamonds). We
found, as would be expected, that apparent brightness
decreases as the color of the diamond becomes
more saturated in the GIA D-to-Z range (including
browns). Grade-determining clouds in the SI2 and I
clarity grades diminish the appearance of fire. Fair
or Poor polish causes both apparent brightness and
fire to diminish; and Fair or Poor symmetry negatively
affects apparent brightness. Neither fluorescence
nor girdle condition showed any effect on
apparent brightness or fire.

and this section further explains:

Other Diamond Quality Factors. Our observer tests
enabled us to examine the effects of other diamond
quality factors (e.g., color, clarity, fluorescence, and
girdle condition) on overall cut appearance.
Although in cases of very low color or clarity, we
found some impact on overall appearance, in general
observers were able to separate these factors out
of their assessments. Therefore, we determined that
the GIA diamond cut grading system does not need
to take these factors into consideration in its final
overall cut quality grades; it applies to all standard
round brilliant cut diamonds, with all clarities, and
across the D-to-Z color range as graded by the GIA
Gem Laboratory.
these quotes are from Page 224 Foundation article - GRADING OVERALL CUT QUALITY GEMS & GEMOLOGY FALL 2004
http://www.gia.edu/pdfs/cut_fall2004.pdf

Thanks Pyramid - I edited the section above to correct the mistake
 

oldminer

Ideal_Rock
Trade
Joined
Sep 3, 2000
Messages
6,322
When a person asks if clarity has an effect on light behavior, there is no answer but "YES". It may be a very slight effect, one of greater impact, or one of huge importance to the light performance. To generalize that SI clarity has no effect or only a little effect when there are better answers is wrong, but not a big sin, either.

Many inclusions admittedly have invisible effect of how nice a diamond looks, but these same inclusions may have a measurable effect if one has good tools to see the exact performance. If the industry sticks to predicting performance by parameters they will have a faulty system which will eventually be recognized for what it is, despite all their marketing skill and advertising money.

Few diamonds, even ones that would seem to be identical in parametric measurement, perform identically when direct measurement of light behavior is applied. Why is this? Inclusions, body color, slight differences in unmeasured parameters, transparency, cleanliness, fluorescence, etc. I don''t think this is difficult to grasp, but the powers of the jewelry grading business seem to have a group brain imperfection which prevents them from realizing how simple the proof is.

We can measure parameters on diamonds we cannot examine in person for screening purposes with a high degree of satisfaction. When we want to know more, we choose to look at the stones to see which we prefer. When we want to know the facts of light behavior, we measure the light behavior directly. No other logical choices make complete sense.
 

Garry H (Cut Nut)

Super_Ideal_Rock
Trade
Joined
Aug 15, 2000
Messages
14,600
Date: 11/24/2006 9:01:37 AM
Author: oldminer
When a person asks if clarity has an effect on light behavior, there is no answer but ''YES''. It may be a very slight effect, one of greater impact, or one of huge importance to the light performance. To generalize that SI clarity has no effect or only a little effect when there are better answers is wrong, but not a big sin, either.

Many inclusions admittedly have invisible effect of how nice a diamond looks, but these same inclusions may have a measurable effect if one has good tools to see the exact performance. If the industry sticks to predicting performance by parameters they will have a faulty system which will eventually be recognized for what it is, despite all their marketing skill and advertising money.

Few diamonds, even ones that would seem to be identical in parametric measurement, perform identically when direct measurement of light behavior is applied. Why is this? Inclusions, body color, slight differences in unmeasured parameters, transparency, cleanliness, fluorescence, etc. I don''t think this is difficult to grasp, but the powers of the jewelry grading business seem to have a group brain imperfection which prevents them from realizing how simple the proof is.

We can measure parameters on diamonds we cannot examine in person for screening purposes with a high degree of satisfaction. When we want to know more, we choose to look at the stones to see which we prefer. When we want to know the facts of light behavior, we measure the light behavior directly. No other logical choices make complete sense.
I think this Is the issue with direct assessment Dave.

You will penalize the price of a diamond TWICE.

Take a one carat diamond that is graded I1 because of a cloud - it might be cut to perfect proportions, but be a bit sleepy. Say it is worth $3500, but if your regime was in place it might be downgraded to less than $3000, where-as there could be a market for this stone that would see it as an eye clean (which it would genuinely be - as are some of the stones listed here https://www.pricescope.com/community/threads/lets-post-our-si-stones-here.36489/= owned by proud clean SI owners).

So in the normal market this stone would probably fetch say $4000 (a genuine SI2 would be worth more than $5000 in this example).

Now is that fair?

I think the market prices clarity and all the other factors quite well at present (except fluoro, BIC''s and FIC''s can be a bargain)
 

C Smith

Shiny_Rock
Joined
Jun 14, 2006
Messages
176
Date: 11/24/2006 3:31:18 PM
Author: Garry H (Cut Nut)

Date: 11/24/2006 9:01:37 AM
Author: oldminer
When a person asks if clarity has an effect on light behavior, there is no answer but ''YES''. It may be a very slight effect, one of greater impact, or one of huge importance to the light performance. To generalize that SI clarity has no effect or only a little effect when there are better answers is wrong, but not a big sin, either.

Many inclusions admittedly have invisible effect of how nice a diamond looks, but these same inclusions may have a measurable effect if one has good tools to see the exact performance. If the industry sticks to predicting performance by parameters they will have a faulty system which will eventually be recognized for what it is, despite all their marketing skill and advertising money.

Few diamonds, even ones that would seem to be identical in parametric measurement, perform identically when direct measurement of light behavior is applied. Why is this? Inclusions, body color, slight differences in unmeasured parameters, transparency, cleanliness, fluorescence, etc. I don''t think this is difficult to grasp, but the powers of the jewelry grading business seem to have a group brain imperfection which prevents them from realizing how simple the proof is.

We can measure parameters on diamonds we cannot examine in person for screening purposes with a high degree of satisfaction. When we want to know more, we choose to look at the stones to see which we prefer. When we want to know the facts of light behavior, we measure the light behavior directly. No other logical choices make complete sense.
I think this Is the issue with direct assessment Dave.

You will penalize the price of a diamond TWICE.

Take a one carat diamond that is graded I1 because of a cloud - it might be cut to perfect proportions, but be a bit sleepy. Say it is worth $3500, but if your regime was in place it might be downgraded to less than $3000, where-as there could be a market for this stone that would see it as an eye clean (which it would genuinely be - as are some of the stones listed here https://www.pricescope.com/community/threads/lets-post-our-si-stones-here.36489/= owned by proud clean SI owners).

So in the normal market this stone would probably fetch say $4000 (a genuine SI2 would be worth more than $5000 in this example).

Now is that fair?

I think the market prices clarity and all the other factors quite well at present (except fluoro, BIC''s and FIC''s can be a bargain)
That is a reasonable way of looking at the situation. I am inclined to agree.
 

oldminer

Ideal_Rock
Trade
Joined
Sep 3, 2000
Messages
6,322
Sorry, but I disagree. A diamond will always be valued by the market as it should be valued, not because of the paper or the style of grading. Our guide is to impart factual data in reports, but the market takes any report and also examines the individual merits of every stone to get to "value". No amount of proper description will lead to a diamond being overly discounted or priced wrong. We're way too smart for that to happen, I hope.

If you want to grade diamonds, do it with direct measurement and be accurate.
If you want to know the value of a diamond, let the free market do its job.

Our mutual limited study of the various labs shows the free market is very capable of making every proper adjustment while still leaving some reasonable amount of bargain possibilities there for careful shoppers.

There should be no fear of grading light performance and cut precision with the most accurate tools. Grading them with less accuracy will do nothing better and may do far worse occasionally.
 

strmrdr

Super_Ideal_Rock
Joined
Nov 1, 2003
Messages
23,295
My take on it is this...
Sure there are si inclusions that can effect performance but most wont to any degree.
A trusted vendor can weed those that do out.

Buy the stone not the grade and get it from someone that you can trust to filter out the woofers.
 
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