GIA rate cut: "good"; HCA rates 1.-

[ABClove]

Can any experts tell me what differences in the HCA rating would cause it to rate higher on a GIA certified "good" cut diamond than an GIA "excellent" cut diamond?

https://myapps.gia.edu/ReportCheckPortal/getReportData.do?&reportno=1136740388&weight=0.70

Thanks!

 

[warheadwl]

I'm a diamond noob here, but the girdle might be too thick for it to be a GIA excellent. I believe the HCA makes assumptions about the girdle being medium.

 

[bagelboy]

I am not clear on what you are asking. What seperates this diamond from a GIA excellent grade is just about everything. The depth, crown angle, pav angle, pav depth. As to why it scores a 1.2 on the HCA, well try leaving the correct depth, table and crown and then change the pavillion angle. The pav angle is like a car engine, it drives everything.

 

[0-0-0]

The HCA favors shallow pavilions. It's not a common combination and the low pavilion angle is likely to cause excessive obstruction (stone goes dark close up).

 

[Karl_K]

The shallow pavilion and the huge girdle are why GIA graded it good.
That particular combo(depending on the particulars) with a more sane girdle could rock in a pendant hence the 1.x hca.

 

[fanofhardrock]

The HCA favors shallow pavilions. It's not a common combination and the low pavilion angle is likely to cause excessive obstruction (stone goes dark close up).

Hi there thbmok - this is really interesting - without meaning to hijack - please can you let me know at what level the pavilion angle becomes low and hence creates obstruction?

thank you!

 

[Karl_K]

The HCA favors shallow pavilions. It's not a common combination and the low pavilion angle is likely to cause excessive obstruction (stone goes dark close up).

In a ring yes, in a pendant with the greater viewing distance it could look great.
The girdle is eating up to much spread for me to consider it even for a pendant however.

 

[Karl_K]

The HCA favors shallow pavilions. It's not a common combination and the low pavilion angle is likely to cause excessive obstruction (stone goes dark close up).

Hi there thbmok - this is really interesting - without meaning to hijack - please can you let me know what level becomes low and creates obstruction?

thank you!

Depends on the crown height but in general anything below 4.6 actual needs to be checked.
ie a 34.5/40.5 might have slight issues, a 36/40.5 might be just fine, both with a 56 table.
The table size, optical symmetry and the angle range(how much variance in the average) as well as lower half numbers can make a huge difference.

 

[denverappraiser]

The girdle is what clobbered this stone on the GIA grading system. It’s got a face up diameter of a 0.62ct and it weighs 0.70. That extra weight is in the girdle. They take a VERY grim stance on this under the grounds that it’s going to be priced like a 0.70 and the customer receives the benefit of a 0.62. I have been known to argue this with the folks at GIA because the problem here is with the price, not the optics. Price is not a gemological property. Is the cut better if it’s cheaper? 0.70 is one of those weight points where the price per carat usually goes up and with a G/VS2 it’s not unusual to see a 25% bump. That’s a strong incentive to do whatever you must to the cutting to get the weight up, even if you have to sell at a ‘discount’ because the cut is only good. You see a lot of strange things at 0.70, 0.50, 1.00, etc. for this reason. As mentioned above, what tends to drive the light return is the pavilion angle and I think there’s a pretty good chance that this is a pretty stone. Is it ‘good’ as GIA called it? Using their rules, absolutely. Is it ‘excellent’ as HCA calls it? As with GIA, under their rules it is. They don’t have the ding for weight ratio that GIA does. Who’s right? I guess that’s for you to decide. The two approaches aren’t looking at the same things.

It's unusual to see a stone like this with GIA paperwork for this reason. EGL may very well call it 'ideal' and at worst would give it no cut grade at all.

 

[0-0-0]

Thanks for chiming in Karl!