2/3 cup Corn Syrup
1/3 cup Water
5 Tbs. Corn Starch
3 to 5 Tsp. Red Food Coloring
2 or 3 Drops Green Food Coloring
1 Drop Peppermint extract, if desired.
Mix the Corn starch thoroughly with the water. Add the Corn Syrup. Mix well. Add red food coloring into the mixture, using only 3 tsp. at first. Then add a couple drops of green food coloring to take the 'pink' edge off the red coloring. If the mixture is too light, add one or two tsp. more red food coloring. Add an extra drop of green food coloring if the mixture gets too pink again (Real blood is slightly on the dark red to reddish brown side, when its not fresh from the heart). Add one drop of Peppermint extract if you wish a fresh minty blood mixture.
I've also been informed that Milk can be added (instead of or with the cornstarch) to keep the blood from being too transparent. White glue was also given as a suggestion, but if you go that route I wouldn't suggest using the mixture on or in your mouth.
1/2 cup water
1 Tbs. cocoa powder
3 or 4 Tbs. corn syrup
1/2 to 1 tsp. red food coloring
2 drops yellow or green food coloring (optional)
Mix the cocoa powder thoroughly into the water before adding the other ingredients - it may help to use warm water. After adding the rest, blend the concoction well, and then wait for it to settle a bit. Either skim the bubbles & chocolate scum off the top with the edge of a Kleenex, or pour the mixture into another container. The longer it sits, the more the cocoa tends to settle to the bottom, which oddly mimics the effect of real blood separating.
If you splatter this mixture onto cloth, it makes neat two-part marks which dry into pretty convincing bloodstains. If you let it run from a victim's mouth and then let it dry, the blood darkens and cakes to the skin in much the same way real blood does. I can also say from personal experience that any washcloth used to wipe down the 'bloody' face afterwards looks remarkably realistic, too.
The mixture may seem odd, but it tastes pretty good, looks surprisingly like real blood, splatters like real blood, dries like real blood. The source of the recipe and had several people asking him if he was really okay after a staged fight.