A note on special photographic techniques applicable to photoelasticity

Pseudosolarization or Sabbattier effect is referred to as the partial reversal of the image obtained when the film is given a limited exposure to uniform light during development with the result that the less exposed area of the negative are preferentially darkened to a certain extent. In photoelasticity, pseudosolarization produces sharply defined equidensity lines or isochromatics of partial fringe order with one line on either side of each integer or half-order fringe. The evaluation of a photoelastic pattern can be facilitated using additional isochromatic lines of fractional order without need for additional equipment as used in fringe multiplication. The classical procedure for producing pseudosolarization effects for photoelastic applications is described for a proper understanding of the necessary conditions. If the photographic conditions and the maximum intensity of light are kept uniform and constant, the accuracy of the method is determined by the precision with which the position of a line can be located.