Check this out [link] and tell me what do you think. I know some artists who use real blood for their paints, i used ketchup and the color is the same! 
fantastic! I would use real blood if it weren't hard to come by. I don't want to hurt any animals or any people (including myself) but at the same time blood gives the piece a very organic feel. I would imagine the blood would dry and change color and thus change the life of the piece as well. It would also be great to experiment with it and other organic things such as plants to see how the two substances interact.