Colorants such as dyes and pigments are used in a wide variety of imaging procedures to provide optical densities for viewable images. Such widely diverse technologies as color photography, diazonium salt coupling, lithographic and relief printing, dye bleach imaging, leuco dye oxidation, sublimination transfer of dyes and photosensitive imaging systems all may use dyes and pigments to form the viewable optical densities. Examples of some of these types of technologies may be found for example in U.S. Pat. Nos. 3,136,637, 3,671,236, 4,307,182, 4,262,087, 4,230,789, 4,212,936, 4,336,323, and the like. In all of these systems the colorant is present in the imageable article within a carrier medium such as a solvent or polymeric binder. In none of these processes does the colorant layer lie below a vapor-deposited metal or graded metal-containing layer. Each of these various imaging technologies has its various benefits and handicaps as measured by their respective complexity.
U.S. Pat. No. 4,271,256 discloses the use of vacuum-deposited organic materials (including dyes) as stripping layers for vapor-deposited metals such as Mg, Mn, Cu, Zn, or Al layers. The preferred metal layer is indium, tin or bismuth and can include an inorganic compound which is a metal sulfide such as CrS, CrS.sub.2, Cr.sub.2 S.sub.3, MoS.sub.2, FeS, FeS.sub.2, CoS, NiS, Ni.sub.2 S, Cu.sub.2 S, Ag.sub.2 S, ZnS, In.sub.2 S.sub.3, In.sub.2 S.sub.2, GoSx (x is a positive number 2.5, or less), SnS, SnS.sub.2, etc.; metal fluorides such as MgF.sub.2, CaF.sub.2, RhF.sub.3, etc.; metal oxides such as MoO.sub.3, InO, In.sub.2 O, In.sub.2 O.sub.3, GeO, etc. Also included are halides selected from AgI, AgBr, AgCl, PbI.sub.2, PbBr.sub.3, PbCl.sub.2, PbF.sub.2, SnI.sub.2, SnCl.sub.2, CuI, CuBr, CuCl, KI, KCl, etc. Such metals as prescribed are imaged by scanning with a laser beam or imaged through a mask by a strobe light and produce strippable images. The images produced by this sytem are weakly adhered to their support (by their very nature they are strippable) and require high energy to produce a visible image.
Vapor-deposited, graded metal/metal oxide or graded metal sulfide layers useful in the present invention are disclosed in U.S. Pat. Nos. 4,364,995 and 4,430,366 which are incorporated herein by reference for the composition of such layers and methods therefor. These layers are constructed of an inorganic matrix containing a dispersed metal (i.e., for the metal/metal oxide layer aluminum particles can be dispersed in an aluminum oxide matrix). As the particle size of the metal increases the color of the layer changes from clear to copper to bronze to black to jet black. By virtue of the technique of application disclosed in U.S. Pat. Nos. 4,364,995 and 4,430,366 this color gradient can be made to occur in the same layer.