Bloodcrafting is the process by which you can enhance armor with the blood of slain Monsters. This process will allow the wearer to have increased health, at the cost of mana. The tradeoff is always 1:1, capping out at an increase of 10 health, at the cost of a loss of 10 mana.
To learn more about the skill, consult your crafting menu ingame.
Consult this crafting Google Doc and flip to the relevant tab for the various items you can make and what you'll need.