This thesis presents the development of a material composed of mixtures of flexible and rigid polyester resins for use in Photoplasticity. Its casting precedure and mechanical and optical behavior were fully studied. The influences of mixture composition, testing temperature and loading and unloading rates on the mechanical and optical material behavior were analysed based on tensile and compressive uniaxial testing data and also through the pure bending of bars and the diametral compression of discs. For this, specimens were observed under loading and unloading and after being unloaded. The Three-dimensional Photoplastic Technique which analyses slices of unloaded but deformed models to simulate Metal Forming problems was applied to the plane compression-of bars. This same problem was studied via a non linear finite element program (NONSAP) which employed the von Mises, Tresca and Drucker-Prager yieldind criterion and also experimentally via the plane compression of aluminun bars with the purpose of comparing results. It may be conclused from these comparisons that the Photoplastic technique employing mixtures of CRYSTIC polyester resins is suitable for determining plastic displacement and plastic strains in forging problems.