Kozibe is name of optical effect like Nail
Head, Fish Eye and etc.
The term Kozibe was introduced by
HRD staff in Antwerp. Kozibe diamonds that show culet through
crown main facets in the face-up position. In particular this
phenomenon led to strong fading of crown brightness for not
very big stones.
This effect is appeared only in diamonds with extra total height (big height is because of either high crown or thick girdle), and that is why it can be used as secondary negative attribute for big stones also.
The value of angle in the field Kozibe in the DiamCalc means angle of tilt when observer can see culet through crown facets.
If the value of angle is negative then it is no need to tilt because culet should be seen through all facets of crown.
The photo real illustration show the kozibe effect. Crown
angle is 35,00 degree, pavilion angle is 50,00 degree, culet
is medium and kozibe is -1,70 degree. Obtained with DiamCalc