An outer cover layer, for a panel that defines a rupturable deployment door of an air bag deployment system in an automotive vehicle, is formed with an invisible pre-weakened tear seam prior to being overlaid onto the panel. The outer cover layer material is pre-weakened along a defined door opening pattern by a single step impression of a variable depth scoring knife into the under surface of cover layer material. The scoring knife contains a series of cutting edges of varying depth and length along its length that coincides with the seam pattern. The scoring may be performed during the conveyance of the cover layer material by making a single impression of the scoring knife into the lower surface thereof so that the maximum cut depth does not penetrate the outer surface of the material.