Here is an example of a typical diamond being sold in your local jewelry store, mall or Internet vendor as something the salesman may tell you is an *excellent* diamond!  Nothing could be further from the truth.  Note carefully ...

• How we can observe various shades of red (from red to pink) and 

• The facets that are reflecting the shadow of the eye of the observer which is positioned perpendicular to the top of the diamond.

• The facets that are blatantly functioning as windows instead of mirrors.  This diamond has terrible leakage. SHEKAKA!  hehe... or is that guano? (anyone remember Pet Detective 2?)

Here is this particular diamond under the BrillianceScope.  Note where the most intense beams of light are coming from.  That's right ... the facets that are pointing the mirrors directly at ya (indicated by the black in the DiamXray).  The lack of black and blatant areas of leakage and faint return cause this diamond to score pretty badly.  Heh... a perfect candidate for a recut!!!