A method for forming coatings of constant thickness on sheets of dielectric substrate (10), which may be curved, includes the step of adhesively applying foil (12) to one side of the dielectric substrate. An electrode (16) is set at a constant distance (D) from the side (10fs) of the substrate to be coated. If the substrate is curved, the electrode is preferably also curved. The region to be coated is evacuated, gaseous precursor materials are infused into the gap, and voltage is applied between the foil (12) and the electrode (16) sufficient to ionize the precursors to a plasma state, whereupon the deposition occurs. The foil may be applied as an adhesive-backed foil. The adhesive may be electrically conductive.