Adjustment to HCA

The HCA is designed to aid a novice consumer or an experienced trade buyer in selecting unseen diamonds as though each diamond were lined up side-by-side. It describes in simple words how each diamonds appearance to a buyer in a retail sales lighting environment. HCA demerits diamonds with sub-optimal performance, such as light loss out the pavilion, excessive head-shadowing or fisheye effects etc.
 
The original design gave an unusually ugly diamond with a crown of 40°, pavilion of 43° and table of 65% a score of ten. However we have found that after adding all the other penalty scores, penalties higher than ten are easily possible. Diamonds with a score of zero are nearly impossible, and not everyone would find such a stone to be the most desirable. For instance the most popular Tolkowsky ‘ideal cut’ scores around one.
 
We will shortly change the basis of the scoring system by a factor of 1.5. Our logic for this change is that the average diamond should score 5. The average of many thousands of web listed certified diamonds that we have analyzed scores around 7.5 on HCA. We feel it is appropriate there fore to simply apply an adjustment factor.
 
Consumers using this service are also advised to confirm their selection with an expert appraiser’s examination. Although the HCA considers the effects of all proportions together, it does not (yet) take account of all factors including the minor facet proportions and symmetry. Also diamonds do not always match their certificates and occasionally lab inconsistencies resulting in ‘soft’ grades.