clotting's all about the platelets, right? - how bout just using plasma so its still your blood but wouldn't clot so bad - spin it round your head on a cord like a centrifuge - might screw up the drying time on the red paint though
a bit of aspirin dissolved in the blood might just help - used in plant shops to make the plants last longer
ah-ha! got it! add some hydrogen peroxide to the blood and it won't clot for a long time! (source: csi tv show episode) won't screw up the paint either but will evaporate
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