The Holloway Cut Adviser (HCA)
is an easy-to-use tool that analyzes a small set of data about a round diamond and renders a score to help the user estimate cut quality. Developed and patented by Garry Holloway in 2001, the HCA tool has been used by thousands of diamond shoppers to sift through vast numbers of diamond listings in order to identify candidates worth considering for purchase. The tool was ground-breaking at the time it was introduced to the market, but due to built-in limitations and the subsequent development of more advanced and accurate diagnostics, the relevancy of HCA as an evaluation tool today is somewhat marginal. The HCA tool requires input of five basic parameters: Depth %, Table %, Crown (angle or %), Pavilion (angle or %), and culet %. It matches those values to predefined tables based upon the developer’s criteria for cut quality.
Holloway Cut Adviser (HCA) Input Screen
How to Understand the HCA Score
Output from the tool renders a 0-10 score, with lower scores indicating better cut quality. However, Mr. Holloway makes clear on his website that the HCA is not intended to be a selection tool - rather, it is meant to eliminate poor performing diamonds. He indicates that a score below 2 eliminates more than 95% of all diamonds. The general guidance is that diamonds scoring between 0-2 are well worth further consideration, while those scoring 2-4 are worth considering “only if the price is right”. Diamonds scoring 5 and below should be considered “only if price is your main criterion”, and those scoring at the bottom, such as very shallow stones with the fish eye effect, should probably not be considered at all.
Somewhat confusing to many users is the statement indicating that diamonds in the 0-2 range should all be considered equally; ‘a diamond with a score of .5 may not be better than one with a score of 1.5.’ This is a recognition that certain variances in a diamond’s proportions, within the top range, involve tradeoffs in individual optical characteristics such as brightness and fire. Differences at this level fall more into the realm of personal preference than objective quality.
Holloway Cut Adviser (HCA) Results
In addition to an overall score, the HCA tool presents individual grades for Fire, Brightness, Scintillation and Spread, with scores of Excellent, Very Good, Good, Fair and Poor. However, it is not clear how those values are arrived at. The evaluation of scintillation is especially questionable considering the factors NOT included in the inputs such as lower girdle facet length and optical symmetry.
Also presented with the results is a color coded chart which indicates where the diamond falls within the proportion charts for GIA Excellent and AGS Ideal. Diamonds that score between 0-2 are deemed to be in an “ideal” range and are categorized as Tolkowsky Ideal Cut (TIC), Fiery Ideal Cut (FIC) or Brilliant Ideal Cut (BIC).
Holloway Cut Adviser (HCA) Results with Proportion Guidelines
Limitations of the HCA Tool
The first and most obvious shortcoming of the HCA tool is the fact that the inputs are limited to a few basic 2-dimensional data points, whereas actual light performance of a diamond is the result of the combined effects of all facets in 3 dimensions. The relatively simple HCA tool does not factor in the contribution of the star facets, upper girdle facets or lower girdle facets, the sum total of which are actually greater than the number of facets that the HCA does consider.
Secondly, the input measurements for the critical crown and pavilion facets are averaged and rounded giving rise to large potential variances in the HCA output scores, depending on the actual measurements of the diamond. An additional and related shortcoming is the fact that facet precision is not accounted for. In the averaging process, a diamond with badly misaligned facets in 3 dimensions can score the same as one with precise alignment.
And finally, the tool does not look at an actual model of the diamond – only an outline of the diamond. The HCA tool can be thought of as a snapshot of the basic silhouette of the diamond, as opposed to a detailed photograph.
When is HCA useful and when is it not?
The HCA tool has been rendered much less useful by cut grading systems released by the major gemological labs (2005/2006) subsequent to the development of the HCA in 2001, and by the increased availability of diagnostic light performance imaging provided by vendors. But because the GIA system is very broad, and because it does not look at the actual diamond, the HCA tool can still be of use in filtering out marginal candidates in the GIA Excellent grade. On the other hand, the light performance based system released by the AGS Laboratories renders the HCA tool completely irrelevant. The AGS system performs sophisticated ray tracing on a 3D model of the actual diamond, accounting for the contribution of every facet of the diamond.
Additional Comments about HCA
In the words of Mr. Holloway “if the supplier has idealscope photos or GemAdviser files of the diamond, then they are more useful than HCA.” We assume that he would agree that the reference to the IdealScope also would apply to an ASET photo since both reflector devices operate similarly, the ASET conveying even more information at a glance.
According to information on the results page of the HCA tool, there appears to have been no further development after Feb. 6, 2003. Both AGS light performance system (2005) and GIA cut grade system (2006) have superseded the release of HCA.
Another statement on the results page also reinforces the view that the HCA is antiquated, if not entirely abandoned. Either by intention or simple oversight the following outdated and inaccurate statement still appears under the output results: “Even though HCA grades cut more effectively than systems like the AGS, it does not yet factor in symmetry and minor facets.” As mentioned above, the light performance system in use by AGS Laboratories since 2005 does in fact evaluate a 3D model of the diamond and is graded using sophisticated ray tracing technology which takes into account the contributions of each and every facet to overall light performance. The suggestion that the HCA tool can grade cut more effectively than the scientifically vetted ray tracing system developed by AGS is clearly misleading.
The Holloway Cut Adviser represented an important advancement in the consumer’s understanding and appreciation of diamond cut quality. And it was extremely useful as a screening tool before the advent of laboratory cut grading and the broad use of reflector tools such as ASET
Research into diamond light performance has progressed significantly in the years since the HCA tool was introduced, rendering its value and relevancy today significantly diminished. But in the absence of other diagnostics, it still has value as a rejection tool to eliminate likely poor performers.