Jim Gurney has a snippet from an interview with Mort Drucker on his blog GurneyJourney
worth a look
Alla Prima Demo
Mort Drucker is awesome.
Love this guy's stuff; David Apatoff talks about him and his work a lot over at his blog Illustration Art. Always pleasing.
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He is amazing. I think it is great he only needs a front and side head shot of a celeb to do those strips for Mad, the rest is just him riffing like jazz.