HOLLOWAY CUT ADVISER | HCA TOOL
Holloway Cut Adviser
The Holloway Cut Adviser ( U.S. Patent 7,251,619 ) estimates a round diamonds appeal based on its potential Light Return, Fire, Scintillation and Spread.
Most people prefer stones that rate 1-2 on a scale where: 0-2 Excellent, 2-4 Very Good, 4-6 Good, 6-8 Fair, and 8-10 Poor. Zero is almost impossible since many of the factors conflict.
You need Total Depth %, Table % and Crown deg and Pavilion deg angles from AGS and 2006 GIA and IGI reports. echo "Some reports list less accurate rounded Crown % and Pavilion %'s; run the stone and if it scores under 2.0, ask the vendor to get you a "; Helium, Sarin or Ogi report with angles.
HCA gets no info on symmetry, polish and minor facets; use it only to reject likely bad performing diamonds to narrow down your final selection. Ideal-Scope images and independent appraisers can help after that.
The tutorial explains more about Cut and diamond beauty. A detailed description of HCA is available at www.diamond-cut.com.au.
Select angles or depth % for Crown and Pavilion. Angles are more accurate.
* Culet % is required if you wish to enter Pavilion %.
Angles vs. Percent for Crown and Pavilion
It is best to input crown and pavilion angles into HCA to reject less beautiful diamonds. We use trigonometry to calculate the angles from % data. Use angles if you have them because:
- %'s are often rounded i.e. 13.3% crown height becomes 13% or 13.5%.
- Pavilion depth % when converted to pavilion angle often understates the pavilion angle by 0.15 deg
- Scanners are not good at measuring culets; a culet reduces the pavilion depth % but does not change the pavilion angle.
- Sarin scanner data is better than Ogi because they calculate the angles and then scale of the %'s. Ogi works the other way round.
"If you only have access to % info (e.g. EGL, IGI or HRD report) then use the %'s to reject known duds, then and ask the supplier to run Sarin angle data on your short list.
If the supplier has idealscope photos or GemAdviser files of the diamond, then they are more useful than HCA.