You are quite lucky then. I have never seen that happen. I have seen them get darker, but I have only seen that treasured slick jet black shiny surface after repeated use and seasoning. In any event, the method you describe it exactly the same process that Lodge uses to pre-season their pans with the exception of the "heavy" part. The use a light coating of fat instead of heavy which is also what most people recommend so that you do not get pools of fat which get sticky and gum up the pan.