Soak in cold water, no additives just plain cold water.
Salt or hot water will set the blood.
Hope that helps
Tonight I went to the butchers and picked up six fresh lamb hides from my
friend's flock. They are all rare breeds, Shetland, Cotswold and Icelandic.
At the moment they are outside on a huge snow drift at -12C (10F) (air
with the projection to go to -20C) cooling off and I have them skin side up.
Last year I had salted them and stacked them right off, but the blood
on the white wool would not come out with washing at all. It seems the salt
sets the blood stain. The tanning solution really stuck to the blooded
areas and stayed stained. Are there any products out there that I can wash
the blood out of the wool with that will not interfere with tanning or
ruining the wool before the hides are salted and dried? I plan on using a
compleatly modern acid/washable tan kit that gave me very good results last
year. I don't have the space to do medieval tanning at the moment. Too
stinky for my basement inside in winter!