Help! (My First Diamond)

[meddelc]

I am contemplating buying this diamond (which is slightly under my budget of $5,000) from Blue Nile. I know it has an HCA score of 4.6, but the GIA report seems great in my amateur opinion. Does anyone have thoughts on why I should not buy this diamond? Or what caused the HCA score to be so bad?

All help would be appreciated! Thanks!

 

[teobdl]

Short answer: you should not buy that diamond.

It has a bad HCA principally because the pavilion angle is very steep. You want a pavilion angle of 40.6-41.0 degrees in a modern round brilliant diamond (description of the cut of the diamond, like the one you picked out). There are different guidelines depending on the cut, but this is the most studied and standardized.

Guidelines (in order of most important to least important--but all still very important)
Pavilion angle: 40.6-41.0
Crown angle: 34.0-35.0
Table: 53-57%
Depth: 60-62.5

If the first 3 are correct, then the last one (depth) will tend to work itself out as long as the girdle is not too thick (aim for slightly thin to medium).

Generally, if you are higher in the pavilion angle (close to 41) then go a little lower in the crown angle (closer to 34). If you are lower in the pavilion (close to 40.6), then go a little higher in the crown (closer to 35).