zoebartlett
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Which is preferred: GIA or AGS
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Regular Guy
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There''s gobs written on this sort of thing on this board, with many easily favoring AGS, and where most experts, when offering a preference, agree AGS is designed to represent the creme of the crop, and where vendors or diamond crafters, as a pattern, just don''t bother to send them to AGS if they don''t think they''ll make their highest grade.
A few points:
a) on color & clarity, no substantive difference, probably. And for the 3rd C, carat..both know how to weigh diamonds.
b) to filter through the mass of info on this board from what''s already been written, consider starting with the FAQ section, where the board administrator has sought to provide readers with the pith instructions.
c) with respect to the "creme of the crop," and in consideration of the fourth C, cut...consider if you were looking for a rich dessert. You were considering a food pyramid, and the richest dessert would be at the top of the pyramid. If your pyramid was five layers high, your rich dessert would be on the top of that heat. That''s GIA. Forget about differences in measurement for the time being. Now consider AGS makes their pyramid 11 layers high. Which dessert will be richer? See this thread in the FAQs to review further.
A few points:
a) on color & clarity, no substantive difference, probably. And for the 3rd C, carat..both know how to weigh diamonds.
b) to filter through the mass of info on this board from what''s already been written, consider starting with the FAQ section, where the board administrator has sought to provide readers with the pith instructions.
c) with respect to the "creme of the crop," and in consideration of the fourth C, cut...consider if you were looking for a rich dessert. You were considering a food pyramid, and the richest dessert would be at the top of the pyramid. If your pyramid was five layers high, your rich dessert would be on the top of that heat. That''s GIA. Forget about differences in measurement for the time being. Now consider AGS makes their pyramid 11 layers high. Which dessert will be richer? See this thread in the FAQs to review further.
luckystar112
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For an easier example to see the difference in how GIA and AGS rate their cuts, go to the halloway cut advisor and type in some dimensions of any diamond you found. You can see that from the diagram that what GIA considers excellent cut, AGS might not.
Hope that helps
Hope that helps
zoebartlett
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Ellen
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zoebartlett
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cavalieredona
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strmrdr
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Cehrabehra
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It depends on what is being graded... it is my understanding that for fancy colors GIA is preferred... and for fancy shapes as well to my knowledge, though it probably doesn''t matter. I think the only place it may matter is in cut, but the way *I* see it is that if you know what numbers you''re looking for, does it matter who tells you you''ve found them?
Regular Guy
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Agreed.
Also, exception to my comments above. Though AGS still uses an option for a cert without a grade, because their data is not rounded, and GIA, with a grade, doesn''t base its grade on anything but posted proportions...I think I''d still generally prefer an AGS without a grade, that has cherry proportions, over a GIA excellent, where I''d have to guess about the goodness of the posted proportions. Assumptions about this non graded AGS certed diamond making or not making the new AGS0 would be based on guesses that I''m not that able to make...that may or may not have to do with who is presenting the stone to AGS.
cavalieredona
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i got what i''ve written from here: http://www.goodoldgold.com/4Cs/NewCutGrading/GIAExAGSIdeal/
it is along article, but very interesting.
besides Hearts and Cupid (H&A, made up in Japn in the 80ths) even is not brither than an diamond with an Exc cut. A diamond is the symbol of love and for this it cannot be measuerd. what is brither, more perfect in the thecnological point of view it is not said that it has to be the best for the human eye. this is what makes a diamond special and unique.
sincerly
D.r Masellis
it is along article, but very interesting.
besides Hearts and Cupid (H&A, made up in Japn in the 80ths) even is not brither than an diamond with an Exc cut. A diamond is the symbol of love and for this it cannot be measuerd. what is brither, more perfect in the thecnological point of view it is not said that it has to be the best for the human eye. this is what makes a diamond special and unique.
sincerly
D.r Masellis
aljdewey
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Both are reputable. I've gotten the sense that AGS is more strict in their grading (particularly as relates to cut), and they seem to be regarded as the 'stricter' lab by several people in the trade whose opinions I very much respect.
I think that perception has become more pronounced since GIA released their cut grading system....a system that many experts in the trade eem to consider too broad in latitude. Their decision to round data has seemed to hurt them moreso.
I think that consumers think GIA is the pinnacle because it's the name that's been touted for years as "the authority"....the standard, as you say. Consumers are more familiar with the GIA name due largely to marketing. That said, I personally feel they've let their distinction slip away as *THE* leader. That's not to say that aren't still an excellent lab, but I don't see them any longer as "the standard".
In the race for labs, I'd stick with AGS or GIA.....they are in a league far above most others. I'm confident enough in GIA that I'd absolutely buy a GIA-graded stone, *as long as* I had other measurement data to rely on.
Having said that, though, I personally consider AGS to be the more impressive lab to me personally. They'd certainly be my preference, all other things being equal.
strmrdr
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very controversial subject with many opinions.
There is a large area of over lap but GIA includes a lot of combos that AGS doesn''t in their top grade.
Personally I think they are both too wide.
An AGS0 will almost always get a GIA EX but the reverse is not even close to being true.
The lab cut grades are a good start and from that standpoint one is as good as the other but neither tells you enough about a diamond to make a decision by itself.
Both AGS and GIA report facet group average angles.
GIA has now moved to using the OGI system for their scans. Previously, OGI was not considered the most accurate scanner results.
Averages are nice when the min and max are close, but if you don''t know how close, they can be very misleading. Then GIA takes the averages and then rounds up, and marks the report "profiles to actual proportions" for rounds.
I sort of agree with Storm''s position of the AGS not being "tight enough", but in some areas they are too tight ( generally lowering the final cut grade due to excellent polish rather than ideal). Personally I like to see some sub-divisions of the cut grade, such as 0-a / 0 -b etc to show the lower and higher end of the 0 cut grade spectrum.
But to AGS''s credit, they did not round up averages of scans that aren''t perfectly exact and can slightly vary in the first place. Plus they have Sarin and Helium scanners. Helium has the reputation of being the most accurate, but the size of the stone that it is capable of scanning, is limited as compared to the Sarin equipment.
GIA has Sarin''s but now that they have affiliated with OGI who is making an "improved more accurate scanner" that they are going to market, so unless the brand scanner is listed on the report, it is sort of a mystery.
I guess I''m sort of surprised that they didn''t choose Sarin, to make a machine that they would market. But I have to admit I don''t think Sarin would stop selling the machine, and in the past, if GIA couldn''t market their gemological products exclusively, they generally wouldn''t add them to the product offerings they selll through Gem Instruments.
To be fair - I guess we''ll need reviews on just how improved the scanner is.
Add to this the availability of direct light return measurements and perhaps that would be a little more conclusive for those who really wish the highest level of detail.
Rockdoc
GIA has now moved to using the OGI system for their scans. Previously, OGI was not considered the most accurate scanner results.
Averages are nice when the min and max are close, but if you don''t know how close, they can be very misleading. Then GIA takes the averages and then rounds up, and marks the report "profiles to actual proportions" for rounds.
I sort of agree with Storm''s position of the AGS not being "tight enough", but in some areas they are too tight ( generally lowering the final cut grade due to excellent polish rather than ideal). Personally I like to see some sub-divisions of the cut grade, such as 0-a / 0 -b etc to show the lower and higher end of the 0 cut grade spectrum.
But to AGS''s credit, they did not round up averages of scans that aren''t perfectly exact and can slightly vary in the first place. Plus they have Sarin and Helium scanners. Helium has the reputation of being the most accurate, but the size of the stone that it is capable of scanning, is limited as compared to the Sarin equipment.
GIA has Sarin''s but now that they have affiliated with OGI who is making an "improved more accurate scanner" that they are going to market, so unless the brand scanner is listed on the report, it is sort of a mystery.
I guess I''m sort of surprised that they didn''t choose Sarin, to make a machine that they would market. But I have to admit I don''t think Sarin would stop selling the machine, and in the past, if GIA couldn''t market their gemological products exclusively, they generally wouldn''t add them to the product offerings they selll through Gem Instruments.
To be fair - I guess we''ll need reviews on just how improved the scanner is.
Add to this the availability of direct light return measurements and perhaps that would be a little more conclusive for those who really wish the highest level of detail.
Rockdoc
stebbo
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Rounds up? Sure on this? I've always been under the impression that they simply round to the nearest multiple of the precision chosen, which could be up or down.
That would mean the max rounding error from the true average pavilion angle would be 0.2 degrees instead of 0.1.
It's just hard to give an overall cut grade because there's just no unaminous opinion as to what is better. Your example of 0-a and 0-b grades, would a more brilliant stone of excellent polish beat a less brilliant stone of ideal polish, even if the difference in brilliance also couldn't be observed without instrumentation?
The AGS's cut grade scale maybe needs to become logarithmic
I agree, the AGS's cut grade is too heavily weighted on polish and symmetry because it should try to represent what the majority of its audience will consider as a better cut. I like how the GIA gives more leeway here.
Hi, Stebbo...... Thanks for the reply.
They round up different facets groups differently. LGF to the nearest 5%. Others vary, usually not as great. CHeck Facetware docs, which should outline it for you.
As far as the AGS 0 for proporions, light return, polish and symmetry. I like that they are tough with each. What I think could be improved he hitting the stone that has a very slight polishing mark a full cut grade lower. So may if the stone has a "1" polish ( and everything else good) , use 0-p1. which wouldn''t be as "heavy handed" to a really incredible diamond.
I don''t think a diamond like the above, is really being "fair" if only for a slight polishing mark to get the Cut Grade dinged.
Rockdoc
They round up different facets groups differently. LGF to the nearest 5%. Others vary, usually not as great. CHeck Facetware docs, which should outline it for you.
As far as the AGS 0 for proporions, light return, polish and symmetry. I like that they are tough with each. What I think could be improved he hitting the stone that has a very slight polishing mark a full cut grade lower. So may if the stone has a "1" polish ( and everything else good) , use 0-p1. which wouldn''t be as "heavy handed" to a really incredible diamond.
I don''t think a diamond like the above, is really being "fair" if only for a slight polishing mark to get the Cut Grade dinged.
Rockdoc
stebbo
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It was the 'up' in the 'round up' that I paused over, but I checked the Facetware docs and they do indeed round (which might be up or down) to the nearest multiple.
I agree. The nice thing about it however is that it allows some fantastic stones to be found without the 'Ideal-0' premium.
Unless the PGS tutorial docs are wrong or misleading, their deduction table suggests that the final cut grade is the sum of many deductions, of which 'polish' is one, and 'finish' is another. Polish counted twice? No wonder it's got too much influence!
I was just saying to John last night during his webinar that they also say the light performance grade is dependent upon (in addition to the obvious factors), weight ratio and durability (??), so I'm not too convinced by the accuracy of these docs. (BTW if you're reading John, any conclusion?)
'Attach file' button isn't working for some reason, but here's the table I was talking about
JohnQuixote
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I was indeed reading, Stebbo, and saw this thread bumped. My understanding has been that weight ratio and durability (both involving girdle thickness at some level) are assessed as proportions factors.
Reference this document from AGSL: http://www.agslab.com/content/sample_dqd_large.html
It indicates that the light performance grade includes brightness, dispersion, contrast and leakage. The proportions factors grade includes girdle, culet, weight ratio, durability and tilt. The finish grade covers P/S.
I've seen this breakdown many times. However I'm not immersed in the PGS yet, so it's possible the discrepancy is a result of a shift (?) I emailed the lab and anticipate a quick official reply. Thanks for bringing it up.
Also - you have the coolest avatar.
stebbo
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kcoursolle
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JohnQuixote
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Zoe and others; sorry for the threadjack.
Stebbo, here is clarification: Of the 11 factors that make up the AGS cut grade, 7 of them are grouped as ‘cumulative' (you add them up). The other 4 – girdle, culet, polish and symmetry are ‘net lowering’. Net lowering deductions only lower the cut grade if they are worse than the sum of the cumulative deductions.
All of the light performance deductions are cumulative.
3 of the 5 proportion deductions are cumulative.
The other 2 are net lowering.
AGS understand that this causes confusion. They will be dropping the ‘Triple 0’ format in the near future (say bye-bye) and the DQD reports will have the specifics of all 11 factors on a fold under flap on AGSL documents. That way a retailer can concentrate of the face of the document when selling to a client who is not so much interested in the why and wherefore of the cut grade. If a techie (known around these parts as a Pricescoper)
comes into his store, he can unfold the flap and discuss, in depth, the factors that account for the cut grade.
Calculation examples:
EXAMPLE 1
Cumulative deductions 1.26
Girdle 1
Polish 2
Culet 0
Symmetry 2
= CUT GRADE 2 (cumulative amounts to 1, but 2 in polish/sym lowers the grade to 2)
EXAMPLE 2
Cumulative deductions 0
Girdle 0
Polish 3
Culet 0
Symmetry 0
= CUT GRADE 3 (cumulative amounts to 0, but 3 in polish lowers the grade to 3)
EXAMPLE 3
Cumulative deductions 2.23
Girdle 0
Polish 1
Culet 0
Symmetry 0
= CUT GRADE 2 (cumulative amounts to 2, and nothing in net lowering categories is lower so it remains 2)
FYI: Cumulative deductions round up at 0.5. So, 1.49 = 1, 1.50 = 2 etc. If this is of interest and you don't mind some tedious polarized conversation
this is elaborated-on back in this post.
ETA: I started a thread regarding the new DQD report format that shows these 11 factors. Continued discussion would probably be appropriate there: https://www.pricescope.com/community/threads/ags-to-introduce-new-dqd-report-format.59690/
Stebbo, here is clarification: Of the 11 factors that make up the AGS cut grade, 7 of them are grouped as ‘cumulative' (you add them up). The other 4 – girdle, culet, polish and symmetry are ‘net lowering’. Net lowering deductions only lower the cut grade if they are worse than the sum of the cumulative deductions.
All of the light performance deductions are cumulative.
3 of the 5 proportion deductions are cumulative.
The other 2 are net lowering.
AGS understand that this causes confusion. They will be dropping the ‘Triple 0’ format in the near future (say bye-bye) and the DQD reports will have the specifics of all 11 factors on a fold under flap on AGSL documents. That way a retailer can concentrate of the face of the document when selling to a client who is not so much interested in the why and wherefore of the cut grade. If a techie (known around these parts as a Pricescoper)
Calculation examples:
EXAMPLE 1
Cumulative deductions 1.26
Girdle 1
Polish 2
Culet 0
Symmetry 2
= CUT GRADE 2 (cumulative amounts to 1, but 2 in polish/sym lowers the grade to 2)
EXAMPLE 2
Cumulative deductions 0
Girdle 0
Polish 3
Culet 0
Symmetry 0
= CUT GRADE 3 (cumulative amounts to 0, but 3 in polish lowers the grade to 3)
EXAMPLE 3
Cumulative deductions 2.23
Girdle 0
Polish 1
Culet 0
Symmetry 0
= CUT GRADE 2 (cumulative amounts to 2, and nothing in net lowering categories is lower so it remains 2)
FYI: Cumulative deductions round up at 0.5. So, 1.49 = 1, 1.50 = 2 etc. If this is of interest and you don't mind some tedious polarized conversation
ETA: I started a thread regarding the new DQD report format that shows these 11 factors. Continued discussion would probably be appropriate there: https://www.pricescope.com/community/threads/ags-to-introduce-new-dqd-report-format.59690/
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JohnQuixote
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While GIA has contracted with OGI in producing the FacetScan scanner GIA still uses interchangeable lens Sarin at the labs as does AGS.
Peace,
Rhino
Good Old Gold
_________________________
Doesn''t that strike you as a little strange????? Use the Sarin in the lab, but sell the OGI to jewelers ?
I think "someone''s slip is showing"...... ( i.e. Gem Instruments wanting exclusivity of products it sells in most instances).
Rockdoc
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