Well, just hitting up Wikipedia seems to lead to some dude named Bruno Guillaume (http://www.artabus.com/guillaume/) who's done some blood painting (http://artscad.com/A.nsf/Opra/SRVV-6MDNX5) (which even stayed pretty red), so it can't be all that impossible. Besides, if I remember anything from good ol' Dorothy Sayers, I gather that blood can stay fluid for a good several minutes (though probably not an hour in air, normally).

As for the extent of the damage – yeah, there was that one comment about hands shaking during the painting....