From the brysonburke website,

 http://www.brysonburke.com/aboutdiamonds.html

The X-Ray Diamond Flow Sorter relies on the fact that diamonds usually fluoresce when exposed to x-ray radiation. If a diamond moving across the x-ray sorter fluoresces, the light is detected, amplified and converted into an electrical signal. An ejection device is triggered and the diamond is physically separated from the rest of the material.

The x-ray diamond recovery machine is capable of detecting diamonds from 1 mm to 25 mm in size, and though diamond recovery is dependent upon many factors, recovery efficiency is greater than 98%. Sophisticated technology also allows for multiple diamond ejections per second. The unit is capable of processing material quickly and efficiently from 0.5 tonne per hour for 2 mm material to 2.5 tonnes per hour for coarse material (> 16 mm in size).

 Now it makes sense to me. If a coating absorbs enough water and causes the diamond to slip of the grease table and if the coating prevents the diamond from fluorescing then it would fall into the waste bin.

 Could this have happened at the SRC lab?  

BGT