Black urad is used in homas and poojas as an offering, for protection from enemies, bad luck and negativity. It is also used as a remedy against Saturn and Rahu.
For Saturn/Shani remedy:
On Saturday fill some oil in a iron pot, put seven pieces of black grams, seven pieces of barley, some coins over it. Now, look into it, then give the alms to a beggar or donate it in a Shani temple. This is result oriented, if performed before 11:00 AM.
For Rahu remedy:
Rahu is attired with blue and is offered black grams and mantharai flower. It is believed that offering the above to Rahu planet brings victory in all leads of life.