The heart side must show eight nearly equally shaped hearts. The heart shape repeats itself, ideally, in a multiple of 22.5°. When grading the heart shapes, the parameters must confirm to some basic guidelines.
The arrow side must reveal eight arrow heads and shafts. The arrow head, formed by the pavilion seen through the bezel facet, must reach the girdle and line up with the shaft. The shafts and the arrow heads must be symmetrical and equally shaped. All the arrows must be clearly visible at the same time when seen from a direction perpendicular to the table. The shafts must touch or nearly touch each other at the base near the center of the brilliant. As with the heart shape the arrow repeats itself in a multiple of 22.5°. The appearance of the arrow shape is influenced by the pavilion angle, the main crown angle, the length of the crown halves and the table size of the brilliant.
Each defect in the patterns is described in a guideline and each guideline is evaluated by the expert system. The result of the evaluation is a penalty. This penalty is multiplied by a weight factor depending on the impact of the guideline on the observation of the patterns. Approval or rejection of the patterns depends on the way the guidelines are violated. To simulate the human behavior a system with soft limits is introduced. Each guideline has a safe zone, border zone and reject zone. A guideline evaluation in the safe zone has zero penalty. In the border zone the guideline evaluation leads to a penalty.
To be able to predict the H&A grade we made a collection of gradually worse penaltys per defect. For each guideline there are three images going from low over medium to a large penalty. Be aware that the penalty is only for the guideline written in the left textbox! So all the images can show several defects which can lead to rejection.

Of course it is useful to have these charts on paper to use in the office, the factory or in your shop. Here you can download a pdf file, filling two A4 pages for the heart guidelines and two for the arrow guidelines.
This movie gives a demo of the grading process for H&A by HRDAntwerp in combination with the WTOCD viewer and expert system.
 

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