Does GIA 35 crown work with 40.6 pavilion?

[thecat]

Hi all, I know GIA does rounding. So how does it affect performance? Or is this good combination? I'm concerned about the pavilion angle being too low. I put a stone on hold but can't get images and sought help in another thread but that thread would mean no vendor can comment. And most of our vendors here have the most expertise knowledge about angles. So I'm starting another thread to just discuss angles without referring to any specified diamond. One of my diamond is 35 crown and 40.8 pavilion and it's a fireball. So I know 35/40.8 works. Hence, can 35/40.6 work when 35 is already working beautifully with 40.8? Thanks for your help.

 

[diamondseeker2006]

Yes, you want a higher crown angle with a lower pavilion angle. The "ideal" (safe) measurements some shoot for are 34.5/40.8. So if the crown angle is higher, you want the PA a little lower (and vice-versa). But often you are okay as long as the CA is 34-35.0 and PA is between 40.6 and 41.0. This stone sounds worth pursuing further.

Are you using the HCA? That is the easiest way to tell if the numbers are okay (as a screening tool). You need either an idealscope or ASET image to see the actual light return and potential leakage. I want to see Excellent on the first three items and Very Good on spread only. You want an overall score of 2.0 or lower (and a score of .8 is NOT better than 1.9). Some stones in the low 2 range are fine, as well, but you really need the light return images to assess those.

https://www.pricescope.com/tools/hca

 

[thecat]

DS, thanks for your help. I did run it thru HCA and the score is 0.8. I like the fat arrows but am concerned at the same time that fat arrows mean lesser scintillation. This diamond has the lowest star facet (45%) I've ever seen in a modern round. I have no idea how star facet/lgf 45%/75% will affect scintillation. Does anyone have any idea?

 

[diamondseeker2006]

I love lgfs of 75. What did the HCA score say for scintillation? If excellent, then there ya go. If not, I'd keep looking.

 

[babydoll_mini]

I recently bought one with 35CA & 40.6PA, it has very very slight partial leakage under the table -- which I don't understand, thought leakage only happens to steeper PA... but overall the stone is very brilliant and fiery

 

[thecat]

I love lgfs of 75. What did the HCA score say for scintillation? If excellent, then there ya go. If not, I'd keep looking.

Scintillation is EX. If I pay for the stone, the stone will be send to JA to be set, right? Anyone knows if JA can then take aset and hearts image? I thought this is a simple enough question but JA rep doesn't seem to get my point and no response to this question.

 

[thecat]

I recently bought one with 35CA & 40.6PA, it has very very slight partial leakage under the table -- which I don't understand, thought leakage only happens to steeper PA... but overall the stone is very brilliant and fiery

Thanks for your sharing. I don't know if I should get this stone as return would be a hassle since I'm not in US. Need to process tax refund and I'm not even certain I can get back the refund.

 

[gm89uk]

JA are able to provide ASET images for up to 3 stones even prior to purchase. I would put it on hold and request it before buying seeing as your return situation is more tricky.

I don't know where you are from but it may be even worthwhile making a trip to the US to pick it up. Would cost the same as shipping!

 

[Diamond_Hawk]

One of my diamond is 35 crown and 40.8 pavilion and it's a fireball. So I know 35/40.8 works. Hence, can 35/40.6 work when 35 is already working beautifully with 40.8? Thanks for your help.

The Cat,

I will keep these comments specific to angle relationships without regard to any stone in particular.

As the HCA indicates, the proportions you listed are worth further investigation. The 35/40.6 could be spectacular (or may have slight light performance concerns) for the precise reason expressed in the thread. The averages of the measured angles will arrive at a number, and that number that is then rounded to 40.6.

The best thing to do is ask for light performance images on a stone with these proportions, then allow experts to give you feedback once you post those images here.

 

[gr8leo87]

A hearts and arrow image will give you a good idea of how much effort went into fashioning that stone. A reasonably symmetrical hearts and arrows is a good sign that there are lesser variations in the facet map of the stone.

Any crown angle between 40.6 and 41.0 coupled with 34-35 degree is worth looking at.

At steeper crown angles of 35.5 and 36.0, a shallower pavillion at 40.6 in the ideal range is more suited. Also 40.6 is by no means a 'shallow' pavillion.

Talking about AGS a 40.4 PA can also receive ideal grading if the stone has certain CA and table size. A 40.4 PA will never receive an Excellent grade by GIA though.

 

[thecat]

A hearts and arrow image will give you a good idea of how much effort went into fashioning that stone. A reasonably symmetrical hearts and arrows is a good sign that there are lesser variations in the facet map of the stone.

Any crown angle between 40.6 and 41.0 coupled with 34-35 degree is worth looking at.

At steeper crown angles of 35.5 and 36.0, a shallower pavillion at 40.6 in the ideal range is more suited. Also 40.6 is by no means a 'shallow' pavillion.

Talking about AGS a 40.4 PA can also receive ideal grading if the stone has certain CA and table size. A 40.4 PA will never receive an Excellent grade by GIA though.

The diamond is overseas to the vendor so that's no image. But the theory behind your recommendation is very sound. I'll keep it in mind for reference. Thank you