A method of manufacturing an image pattern for a security device, comprising:
- (a) providing a metallised substrate comprising a substrate material having a first metal layer thereon on a first surface of the substrate material, the first metal layer being soluble in a first etchant substance;
- (b) applying a first photosensitive resist layer to the first metal layer, the first photosensitive resist layer comprising a thermally-activatable cross-linking agent which, is operable to preferentially cross-link functional groups of a selected class, which functional groups are not present in the first photosensitive resist layer upon application to the first metal layer;
- (c) exposing the first photosensitive resist layer to radiation of a wavelength to which the resist layer is responsive through a patterned mask, wherein the patterned mask comprises first pattern elements in which the mask is substantially opaque to the radiation and second pattern elements in which the mask is substantially transparent to the radiation, whereupon the exposed second pattern elements of the first photosensitive resist layer react resulting in increased solubility in a second etchant substance, the non-exposed first pattern elements remaining relatively insoluble by the second etchant substance;
- (d) exposing the first photosensitive resist layer to a first reactant substance, the first reactant substance reacting with the exposed second pattern elements of the first photosensitive resist layer to produce at least one functional group of the selected class, the first reactant substance substantially not reacting with the unexposed first pattern elements of the first photosensitive resist layer:
- (e) activating the cross-linking agent in the first photosensitive resist layer such that cross-links are formed between the at least one functional group of the selected class in the exposed second pattern elements, whereby the solubility of the exposed second pattern elements of the first photosensitive resist layer in the second etchant substance is decreased;
- (f) exposing the first and second pattern elements of the first photosensitive resist layer to radiation of a wavelength to which the resist layer is responsive whereupon the newly-exposed first pattern elements of the first photosensitive resist layer react, resulting in increased solubility by the second etchant substance, the second pattern elements remaining relatively insoluble by the second etchant substance;
- and
- (g) applying the first and second etchant substances to the substrate whereupon the first pattern elements of both the first resist layer and the first metal layer are dissolved, the remaining second pattern elements of the first metal layer forming an image pattern;
- wherein
- in step (g) the first pattern elements of both the first resist layer and the first metal layer are soluble in the same first etchant substance, the first pattern elements of the first metal layer and of the first resist layer are dissolved in a single etching procedure.