Method of engraving printing plates of forms by means of energy beams, especially laser beams

A method for engraving a printing surface with an energy beam, said method comprising:

• preparing a reflective mask having a plurality of elemental areas which are adapted to reflect and to pass varying amounts of energy from said energy beam, the amount of energy passable by any given area being representative of the tone gradation of a corresponding area of an original to be engraved upon said printing surface and subsequently reproduced thereby in a printing process,
• said preparing step including the steps of providing a basic mask material which substantially reflects said energy beam and forming a plurality of individual cells of differing reflectivity in said mask, said reflectivity being inversely related to the depths of corresponding cells to be engraved in said printing surface whereby the reflectivity of the cells in any given area of said mask with respect to the energy beam is inversely proportional to the tone gradation of a corresponding area of the original to be engraved into said printing surface, and energy not reflected is substantially passed through the mask,
• providing an energy beam of substantially constant energy value, said energy beam having a cross sectional area encompassing a plurality of said elemental areas over the masked printing surface, and
• interposing said mask between said printing surface and the source of said energy beam such that said energy beam simultaneously illuminates a plurality of said individual cells, whereby said elemental areas are etched onto said printing surface corresponding to the amount of energy passed through respectively associated elemental areas of said mask.