excess of 1 0 and a d min below 0 10 most means of supplying the nitrate ion into the composition are satisfactory e g metal salts acid salts mixtures of acids and salts and other means of supplying the ion are useful for example nitrates of zinc cadmium potassium calcium zirconyl nickel aluminum chromium iron copper magnesium lead and cobalt ammonium nitrate and cerous ammonium nitrate have been used the nitrate salt component of the present invention must be present in a form within the imaging layer so that hno 3 no no 2 or n 2 o 4 will be provided within the layer when it is heated to a temperature no greater than 200 u00b0 c for 60 seconds and preferably no greater than 160 u00b0 c for 60 or most preferably 30 seconds this may be accomplished with many different types of salts both organic and inorganic and in variously different types of constructions the most convenient way of providing such thermal oxidant providing nitrate salts is to provide a hydrated nitrate salt such as aluminum nitrate nonahydrate al no 3 2 9h 2 o this salt when heated in a binder will generate hno 3 no no 2 and or n 2 o 4 in various amounts the binder should not be at such a high ph that the liberated nitric acid would be immediately neutralized as this would adversely affect the oxidizing capability of the system it is not essential that a completely acidic or neutral ph environment be provided but ph levels above 8 5 may in many cases completely prevent oxidation it is therefore desired that the nitrate salt containing layer have a.