About shadow sharpeners

[Anselmo P�rez Serrada]

One last thing, excuse my ignorance, but what is a shadow sharpener 
and what is its use?
Thanks
AP

Hi all, I am as ignorant as Alexei, so I'd gratefully apreciate any hint 
(or link) on what a shadow sharpener exactly is.

Best wishes,

Anselmo



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