For our recent stage production of The Revenger's Tragedy, I needed to come up with an economical and effective way to make several gallons of realistic stage blood. Normally, I would have used one of the many corn syrup based recipes that have been popular for decades, but the Technical Director wanted to avoid sugary recipes due to the risk of attracting ants and other nasty creatures into the theatre.
In addition, the costume designer needed to be able to wash the blood completely out of the costumes between performances, the set designer wanted to prevent staining the set, and (since there was a possibility of splashing the audience) we needed to be able to assure audience members that their clothes would not be ruined. This pretty much meant no red food coloring could be in the recipe either.
Furthermore, the blood would have to be visible on both light and dark surfaces and work in several different delivery devices, including air cannons, pneumatic squibs, squeeze bulbs, blood bags and a trick knife. (For a truly excellent pneumatic squib, see Crosius' phenomenal Instructible here: http://www.instructables.com/id/Pneumatic-Squib-Tutorial/
After experimenting with several formulas I came up with this one, which met all of the needs listed above very well, and only costs about $13.00 a gallon. Compared to some commercial blood at $60.00 a gallon or more, this is quite a bargain. If you need buckets of blood for any reason, give this a try.