Note If you use the oven's self-clean cycle, you do not need to remove the hard deposits from the oven before kashering.
If the oven is not self-cleaning, you must remove (clean off or burn off) any deposits on the walls, racks, and window. If the stains or deposits do not come off after two cycles of using a strong oven cleaner such as Easy Off, the oven is considered sufficiently clean. Weaker oven cleaners that do not remove deposits may not be relied on.