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HCA - Defining the Beauty and Desirability of Round Brilliant Diamonds

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 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.
 
Dec. 15, 2001. HCA was adjusted so that any stone that scored 3 would then score 2. After some more research it was decided that adjustment went a little too far, In February 2003 we decided to adjust the penalty to a midway point.
 
Other changes have been made too the light return scores:
 
1. The penalty for table sizes has been tightened to 55% to 56%. Above and below this range a gradual penalty is added to an extended range from 75% to 40% tables.
 
2. Some shallower proportion combinations have been penalised more heavily. This is a result of discussion with scientists from OctoNus and Moscow State Uni and diamond cutter Brian Gavin. This was followed by surveys which showed that preferences for say 40.0 degree pavilion combined with 33 crown angle varied; some people love the star that never goes away, others hate the effect. Overall as Dave Atlas has said, it is safer to guide people toward "usual and normally accepted cuts".
 
We hope that these changes have not inconvenienced anyone overly, but as stated in the fine print: "This system is being continually fine-tuned and results may change without notice".
 
You can read more about the theory and mechanisms behind HCA at www.diamond-cut.com.au - although some of the information there will not reflect all changes.
 
We hope over time that the 'average' stone improves as a result of sales pressure from your use of this service.
 
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 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.
 

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