Firstly I want to warn everyone to never use your own blood in the creation of this.
(1) First you must acquire the blood. (This can be purchased from a grocery store or butchers or excess blood may be drained from any meat produce bought at the grocery store.)
(2) Once you have acquired enough, add finely ground sea salt (This needs to be an almost powdered form). The ratio of salt to blood is 1 part salt to 8 parts blood.
(3) Now you have your blood ink. Note that you should always create new ink when needed as i may expire between use and should not be stored.