That doesn't apply to a negations of the verb être
See point 4 here: http://french.about.com/od/grammar/a/de-vs-du-de-la-des_2.htm
Thanks for your question, cravatenmja, and thanks for the link patlaf! Although I use it correctly (out of habit), I didn't realize there was a distinction or a rule, so this is helpful.
Seems to me that the opposite would be more quotable... "Soldiers are artists. They paint in blood and guts."