stage blood
Stage Blood

A fairly realistic prop blood for stage or screen can be made from Karo syrup and red food coloring. Mix enough food coloring into the syrup to produce a nice, deep blood red. Adding photographer's wetting agent (Kodak Photo Flo) at about one capful per cup helps to improve the flow of the "blood" as well as allowing it to soak more realistically into clothing and other fabric. If you plan on using the blood on or near your mouth, don't add the Photo Flo. Needless to say, assume this will stain anything and everything it touches, so don't use it over the carpet, and don't get it on any clothing you may want to wear again. (Okay, it isn't really this likely to stain, but better safe than sorry.) A few drops of household detergent will make it a bit easier to clean.

Stage blood
The folks at Priscilla's Performing Arts in Granbury, Texas developed this variation. It "was invented to provide a source for safe, non-toxic stage blood." It requires:

1 cup (250mL) creamy Peanut Butter - they recommend Critic's Choice or Peter Pan
1 qt. (1 L) White Corn Syrup (Cheapest brand you can find - they tend to be thicker)
cup (125mL) Non-suds soap (they use LOC Regular, which is only available through Amway - there are alternatives)
1 oz. (30mL) red food color
15 - 17 drops blue food color
Mix the peanut butter with enough corn syrup to make it runny. Add soap and food colors and mix well. Add remaining corn syrup and shake until a good solution is obtained.
A reader who works in theatre sends in this variation:

To make a thinner blood that will flow better, use a whole bottle of dark corn syrup and 2 big spoonfuls of peanut butter. Add red food coloring until the mixture is pretty red, and then add a couple drops of blue to make it darker. The food coloring, if all goes as planned, will stick to the peanut butter and not to the fabric. Add a little alcohol (ex. Vodka) which, as the contributor writes, "not only makes the blood thinner, it also keeps the tons of sugar from 'candying' and getting hard and nasty".

Even more blood tips, submitted by Alex Erkiletian

"To the first recipe: for every amount of red food color, you should add half that amount in egg yellow food color (example: 1 bottle of red + 1/2 bottle of egg yellow). The yellow should be put into the mix last; it will mix with the mixture better. This addition of yellow will give the blood a brownish hue when it runs off the skin or surfaces in general. If the blood must be seen on a dark surface or person you can make it more opaque by adding coffee cream. Don't add the coffee cream until you are ready to use the blood as it will spoil quickly. If you want to use something that won't spoil so fast, you can sift flower into the mixture; just stir it before use. If you want to put the stuff in your mouth, you should make a mixture with no Photo Flo; add a little mint extract for taste."