whats a good recipe for believable blood?

currently googleling for ideas.

but any personal experiences with a winning concoction?

Corn syrup, flour, food colouring and baby oil. I seem to remember making a good fake blood from those ingredients. Can't remember the ammounts though.
When colouring add in one drop of blue or green colour. Gives a more realistic colour.

For black and white film you could follow in the footsteps of a great master, use chocolate syrup. Hitchcock allegedly used it in psycho.

Clear corn syrup (Karo is one brand name)
Water
Red food color
Blue food color

Do several tests to find out the mixture you like best - it
usually takes only a drop or two of blue per quart. I use
black coffee rather than water to thin the syrup and
make it more opaque.

Add a little photoflo (from Kodak) so it doesn't bead up as
much. But not if you're using it in an actors mouth! Add
a little liquid dish washing soap to make it stain less.

corn syrup
red food coloring
Hershey's syrup

one bottle of coloring to one bottle of corn syrup,add Hershey's syrup untill dark enough. It looks great and does not tast bad either

Add some oat meal for chunky blood (brain matter, etc.).

And a touch of dish soap if you want it more runny and frothy!

ive made a few. the best one seems to be just normal flour with water. just gotta get the colour right.

i made one outta dishwashing liquid, which looks like its gonna be great for big pools of blood, and or drenching body parts in.

i hope it looks good on camera!

also. is it enough just to put the fake blood on the actor or should i be trying to create a kinda wound looking thing first.
i know that ideally you'd have a wound. but is it completely necessary to sell it to the audience?

You could use some liquid latex to build up a wound.

Kero syrup (get the low sugar kind - your actors will thank you for the better taste and it makes no difference in the look)
water
non-dairy creamer (makes it look cloudy and opac as opposed to translucent)
red food coloring
blue food coloring