I would use lard or Crisco. If you use oil it will burn and cause a sticky goo film on the cookware. When I buy new cast iron, I coat it with Crisco and heat it for 20 min. at 350', let it air cool, wipe out the excess grease and place back in my oven and just leave it there to be heated and cooled everytime I use the oven. After a while the cast iron is black and seasoned perfectly. Perfect castiron is black and very smooth and shinny. You might have to scape the carbon build up after repeated heatings to get to the shinny layer.