These Black Sesame (Til) seeds are used for purifying the body and Healing. Water boiled with these seeds makes body pure. Black til is mixed in either milk/water and then offered to Lord Shiva in the form of Abhishek. It is equivalent to doing abhishek with punchamitra. This seed is very dear to the pitrs. Shastras say that it make the person cross the Vaitarini - the sea of bad karma. One has to cross the Vaitarini to reach Vaikunta, During the shraadh ceremony the kartha makes a special offering of black til or black sesame seeds to pitrs.