Recipies

My go-to recipe is Karo light corn syrup for a base, then I add plenty of red food coloring.

To get the red pigment level balanced it's important to note that the mixture will appear darker and more opaque when in a large volume.  Since the blood will often be used in small amounts, it's important to pigment it to the right/desired translucency when spread thin.  To test this I take either a popsicle stick or plastic spoon and draw a black circle on it with a sharpie.   I then dip that into the base mix so I can see how it looks on a light-colored surface (the stick/spoon) a dark surface (the circle) and based on the difference between the two surfaces I can gauge translucency.

This gives me a generic thick and bright red base, which I then use to make variations depending on use.

For darker blood, I add a few drops of green food coloring.  Green will darken the red without shifting its hue, whereas adding blue would darken it and shift the hue more to purple.  There may be some situations where you want a bit of blue, or yellow, but that's really up to you.

Next, I can thin the blood with water to create flowing/dripping blood as needed.  How much water you add will depend on how you want to use the blood.  For nice slow drips, you can leave it thick.  For spraying or pumping it, you can add more water to really thin it down.

If you thin the blood a lot you may also want to add a bit more food coloring if it starts to look too translucent for your intended use.

At this point, you have mouth-safe blood.

If the blood will be used on the skin, on clothing, props, etc, you may want to add a bit of liquid laundry detergent to it (not a lot) to help prevent/reduce staining.  If you add too much detergent, things can foam up if agitated, so use it sparingly.

For permanent blood (like on a prop or set dressing) I use a clear glue base rather than Karo, and don't dilute it with anything.  The clear glues often dry nice and shiny, so the blood can look wet for years.

That said, for most of my projects these days I use off-the-shelf blood.  I'm a big fan of "My Blood" in their "Three Kings" shade of red.   You can find it at some makeup shops, or online through makeup shops. 

My absolute favorite is Fleet Street Bloodworks - Drying Blood by PPI.  It's a little expensive, but it creates a realistic looking dried blood, which I find I use a lot more often than wet bloods.

Ben Nye makes a great blood pigment powder that you can use as an alternative to food coloring.  It's great when you need to mix up many gallons of blood.   A little bit of that pigment goes a really long way.

Then you have gel/paste bloods that are good for building up depth.

/Chris