.4 pavillion degree change moves HCA by 3 numbers?

[dumbo]

Question on the HCA; playing around with the numbers, the pavillon angle changing by .4 degrees moved the HCA in one example from 1.6 to 4.7. It doesn't seem like much of a change: if this is true, and all the numbers are within good range otherwise, why would a diamond cutter do this? Or is the HCA not that accurate?

62 depth
58 table
34 crown
41.4 pavillon

 

[pfunk]

Could be to squeeze some extra weight to prevent the stone from falling below a certain carat weight cut off. For example, to make sure the stone achieves a full 1 carat in weight as opposed to dropping below 1. The price for a 1 carat is usually substantially more than a 0.95 for example.

 

[Karl_K]

yes 41 to 41.4 is a huge jump.
At 41.4 the diamond is going to have color entrapment as well as leakage under the table.

In the ags system it goes from a 0 with most lowers to ags4-5 depending on lowers.

 

[Karl_K]

As to why it is done is to save weight and make a heavier diamond.
It would likely still get gia EX depending on the lowers if I recall correctly.

edit: confirmed it would get gia EX with most common lowers.

 

[dumbo]

Thanks, that makes sense. Diamond is 2.1, so it probably would have fallen under 2 had they taken the pavillon down to sub 41 degrees. Didn't know it made such a huge difference in light reflection!