A method of making a mask or an electronic part, for example a printed circuit, comprises the steps of delivering heat in a desired pattern to a precursor of the mask or electronic part, the precursor comprising a surface coated with a coating, the coating comprising a heat-sensitive composition itself comprising an aqueous developer soluble polymeric substance and a compound which reduces the aqueous developer solubility of the polymeric substance, wherein the aqueous developer solubility of the composition is not increased by incident UV radiation but is increased by the delivery of heat; then developing the precursor to remove the heat-sensitive composition in regions to which the heat was delivered. In the case of a printed circuit precursor the surface may be then etched in conventional manner to yield the required printed circuit.