The objective of this project is the automation of polish grading. Next to the evaluation of polish lines also a range of other surface defects needs to be detected. The final goal is a quantification of the polish in an objective and standardized manner.  The polish grading is done manually with the aid of a loupe 10x or microscope. For the polisher the loupe is not the only aid to evaluate polish lines during polishing. The Avalon device visualizes the polishing lines of a facet being polished. Both polishers and graders can evaluate polish in a different way because of the different viewing conditions. This can lead to inconsistency in the evaluation of the polish grade and discussions between graders and polishers. Intelligent automation can provide accurate and consistent information on the polish grade. The nessecary equipment must be developed for both polishers and graders. The first part of the project concentrated on the nature of all the defects influencing the polish.

In the picture on the left we see an image of polishing lines on a pavilion half. Heavy polishing lines are clearly visible as a pattern of white stripes under grazing light. The polish grade will depend on the visibility of the polishing lines


The next defect is extra facets. These appear by accident or to mask remainders of the rough diamond. In both cases they lead to a downgrade of the polish.



Burnmarks have the look of faint oil stains on the facet. The visibility can increase looking at the defect through the diamond from the opposite side. The cause of burnmarks is oxidation of the surface due to overheating the diamond during polishing.


Fine Scratches can lead to a downgrade of the polish grade. This depends on the visibility. The grading rules state that the grading has to been done looking at the diamond from the crown side with a loupe 10x. Graders often tend to look through the pavilion side at scratches on the table. This can lead to discussions between grading labs and polishers about the correct polish grade.

Small pits in the facet are judged by there visibility. Some common reasons for pits are damages after polishing, left overs from rough, or break out of micro crystals.  



There is a solution for visualizing polish lines, Avalon, but there is no measure for the visibility of these lines. This means that production time can increase, trying to remove details beyond visibility. The challenge of this project was to safeguard the quality but decrease production time per diamond.
The first study tried to capture all classical parameters for surface roughness as being used in mechanical engineering. To measure the surface roughness we used a PSI device (Phase Shifting Interferometry) at VITO. The conclusion of this first test was disappointing, there was no link between human inspection and classical surface roughness parameters. Further investigations were focused on the mathematical relation between Avalon images and height data from the PSI. This finally leaded to a measure for the visibility of polishing lines calculated out of improved Avalon images. These results gave birth to a new device, AvalonPlus.

At this moment the prototype of AvalonPlus is used to gather data in cooperation with the diamond industry. The aim is to create a standard polish grade combined with objective and consistent measurements used by industry and labs. Transparent, measurable, rules for polish are a benefit for the whole diamond sector and the consumer.
Everything you would like to know about Surface Morphology of Diamond (SUMODI)...
Dr. Peter ter Heerdt, WTOCD (Scientific and Technical Research Center for Diamond), Lier, Belgium.

Interested in a demo of AvalonPlus...
Erik Wanten, WTOCD (Scientific and Technical Research Center for Diamond), Lier, Belgium.