The caustics created from reflections of light rays at the vicinity of stress singularities and other stress concentrations in an isotropic and elastic plate submitted to a plane-stress mode of deformation yield important information concerning the order of singularity of the stress intensity or concentration factor at these particular points of a stress field. All information was extracted from particular measurements of the longitudinal or transverse diameters of the caustics, based on basic properties of caustics. In this paper some further properties were found, which are very useful in evaluating the stress field creating the caustic, which make the respective measurements independent of the angle of orientation of the caustic and more reliable than previously.