Find your diamond
Find your jewelry
shape
carat
color
clarity

Question on ''low'' crown angles

Status
Not open for further replies. Please create a new topic or request for this thread to be opened.
B

BobR

Shiny_Rock
Joined
Oct 27, 2009
Messages
105
Hi
I''m looking at acquiring some diamonds for a pendant.
Looking at posts over the last couple of months it seems the standard recommendation for proportion combos is 34-35 ca/40.6/41 pa.
My questions are:-
1) Why limit to this range when there are combos outside this range that are qualify for both GIA Ex and AGS Ideal??
For example, with table 57 AGS grade 31/41.8 as ideal, (its GIA VG); but 31.5/41.8 gets a GIA Ex, AGS Gold (2 dimension??) and AGSPGS (3 dimension???) (AGS gradings via Octonus website). The same point applies for the opposite end of range (36/40.6 scores GIA Ex/AGS Ideal). (all these grades are of course dependent on specified star/lgf and girdle parameters)

2) What are the expected differences (presumably perceived as adverse??) between lower crown angles and recommended (Tolkowski??) angles.

3) If the recommended combos are based on Tolkowski, what do the experts believe the basis is for both GIA and AGS to ''wander'' significantly from this in their Ex/Id gradings?

My wife has a pair of 3 stud earrings and we believe the best performing stones have 55table/32.5ca/41.4 pa and 56/32/41.2 combos. These stones are two of three in the set that qualify for both GIA Ex/AGS ideal based on proportions.
Unfortunately none of the stones fall in the recommended range to allow direct comparison.

Thanks for any and all insights
Bob
 
Date: 12/2/2009 6:08:52 AM
Author:BobR
Hi
I'm looking at acquiring some diamonds for a pendant.
Looking at posts over the last couple of months it seems the standard recommendation for proportion combos is 34-35 ca/40.6/41 pa.
My questions are:-
1) Why limit to this range when there are combos outside this range that are qualify for both GIA Ex and AGS Ideal??
For example, with table 57 AGS grade 31/41.8 as ideal, (its GIA VG); but 31.5/41.8 gets a GIA Ex, AGS Gold (2 dimension??) and AGSPGS (3 dimension???) (AGS gradings via Octonus website). The same point applies for the opposite end of range (36/40.6 scores GIA Ex/AGS Ideal). (all these grades are of course dependent on specified star/lgf and girdle parameters)

2) What are the expected differences (presumably perceived as adverse??) between lower crown angles and recommended (Tolkowski??) angles.

3) If the recommended combos are based on Tolkowski, what do the experts believe the basis is for both GIA and AGS to 'wander' significantly from this in their Ex/Id gradings?

My wife has a pair of 3 stud earrings and we believe the best performing stones have 55table/32.5ca/41.4 pa and 56/32/41.2 combos. These stones are two of three in the set that qualify for both GIA Ex/AGS ideal based on proportions.
Unfortunately none of the stones fall in the recommended range to allow direct comparison.

Thanks for any and all insights
Bob
Click to expand...
Those figures given are guidelines as a reasonably safe way to find a well cut diamond. There are other proportion configurations which can work, however even if a diamond gets a top lab cut grade it doesn't necessarily follow it is going to be a great looking diamond. For instance take the inverse relationship between crown and pavilion angles, a shallow crown and much steeper pavilion angle might earn a respectable cut grade but a pavilion angle as steep as 41.8 has its own undesirable issues such as leakage regardless of having a shallower crown, colour entrapment in some cases and a greater tendency to show dirt. Shallower crown angles can in some cases mean a diamond won't show as much fire or coloured light. Add to that a crown angle of 32.5 degrees or below coupled with a very thin girdle, the general concensus is that there could be possible durability issues.

So really yes there certainly are other proportion combos which can result in a great looking diamond but for those of us working online with limited info to go on, we have to be cautious when advising to try to make sure those who follow our advice end up with a beautiful diamond. This is much easier with these other proportion combos if we have images to go on, if not it can be a gamble.
 
Lorelei,
Thanks for the comments, but, to play devils advocate, GIA and AGS are not awarduing a ''respectable'' cut grade - they''re both awarding the HIGHEST grade - why then if one of the angles has potential known issues??
Bob
 
Date: 12/2/2009 6:26:58 AM
Author: BobR
Lorelei,
Thanks for the comments, but, to play devils advocate, GIA and AGS are not awarduing a ''respectable'' cut grade - they''re both awarding the HIGHEST grade - why then if one of the angles has potential known issues??
Bob
Click to expand...
Sorry I used that term meaning where you wrote GIA VG. I will post some threads you might find interesting as there are some '' lively'' discussions on this very issue!
 
Thanks Lorelei
Look forward to the threads!!
Bob
 
Date: 12/2/2009 6:34:03 AM
Author: BobR
Thanks Lorelei
Look forward to the threads!!
Bob
Click to expand...
These should keep you busy!! Bear in mind also GIA cut grading is proportion based unlike AGS which is for AGS0 performance based. AGS cut grading is usually considered preferable to GIA. Also with some of diamonds that might be ' borderline' things like painting, various other cutting techniques, length of lower girdle facets and so on can have a positive or negative effect or influence beauty and performance.

GIA Excellent - let the buyer beware

Consumer Advisory - GIA cut grade rounding problems

GIA Excellent - why doesn't it add up?

Why did GIA include steep deep in GIA Excellent?

An AGS view of GIA steep deep Excellent
 
Tolkowsky's ideal is a good balance of characteristics.

Tolkowsky angles 34.5/40.8 are "safe". They are fairly tolerant of a few minor cutting issues. Nobody ever got fired for using a Tolkowsky stone and very few clients will be disappointed.

The range of cut proportions from GIA or AGS caters for a wider range of tastes - including those who dislike the look and behavior of a Tolkowsky type.
The GIA/AGS grading systems also cater for stones that have more brightness at the expense of fire, or more fire at the expense of brightness.

For example; 33.0/41.0 can work very well, as can certain other proportion combinations. But those stones have a different look to them and are best left for people who really know what they like.
 
Thanks for comments
Lorelei
the subject matter in the threads you gave all suggest they are about issues with GIA grading system, but my points are about ranges where both GIA and AGS agree ( overlap) on CA/PA combos, In the first thread Brian Gavin talks about issues with a 41.8 pa - and yet both GIA and AGS (2 dimension and 3 dimension???) allow for 31.5/41.8 as Ex/Id(0).

FB
Your points appeal to me and if I recall in HCA somewhere it suggests that higher ca (with lower pa) give fire at expense of brilliance ( is this the right way round??). If so I''m confused because its the fire in our 32 and 32.5 ca earring stones that appeals to my wife and myself!!

Bob
 
Bob

Yes, generally speaking, flat crown/steep pavilion = less fire/more brightness. Large crown/shallow pavilion = more fire/less brightness.
But push the limits too far and you end up with other problems - fish eye, obstruction and so on.

The way that the stones emit fire also differs between a Tokowsky (TIC) and the fiery (FIC) or brilliant (BIC) variants - according to how my eyes perceive it.
It seems as if a TIC has a large number of medium-sized flashes of fire set against a slightly darker stone whcih accentuates the flashes. BIC has fewer flashes and they are less prominent because they are against a brighter background that masks them slightly, but the fiery flashes in a BIC tend to be larger and of longer duration than those in a TIC.
 
Going off at a tangent slightly, 1 of the stones I''ve been offered is a 0.63 GIA FSI1 with 57 table/35.5 ca/40.8 pa. This seems just ok in terms of angles, but when I look at report checker there are no clarity characteristics. Does this suggest that clouds are the only grade maker and could this be a problem??
thanks
Bob
 
Date: 12/2/2009 8:17:36 AM
Author: BobR
Going off at a tangent slightly, 1 of the stones I''ve been offered is a 0.63 GIA FSI1 with 57 table/35.5 ca/40.8 pa. This seems just ok in terms of angles, but when I look at report checker there are no clarity characteristics. Does this suggest that clouds are the only grade maker and could this be a problem??

thanks

Bob
Click to expand...
Angles are slightly off, depending on the rounding/averaging of the numbers and lower half, can perform well or show leakage.

The report check link?
 
Date: 12/2/2009 8:17:36 AM
Author: BobR
Going off at a tangent slightly, 1 of the stones I''ve been offered is a 0.63 GIA FSI1 with 57 table/35.5 ca/40.8 pa. This seems just ok in terms of angles, but when I look at report checker there are no clarity characteristics. Does this suggest that clouds are the only grade maker and could this be a problem??
thanks
Bob
Click to expand...
Do you have the report check link or the report number to get it please?
 
its 1116163108 (0.63ct)
 
Status
Not open for further replies. Please create a new topic or request for this thread to be opened.
GET 3 FREE HCA RESULTS JOIN THE FORUM. ASK FOR HELP
Jewelry Blog
PriceScope-Concierge-Ad
Find prime cuts.
Top