The present work aims to study composite materials, more precisely, certain type of reinforced fiberglass polyester resin with orthotropic, birefringent and transparency properties, through the development of appropriate methods for its mechanical and optical characterization. A kind fiberglass available on the Brazilian market was used: roving 374, (by Ocfibras) which was combines with crystic 199 P.A rigid resin matrix (by Leo Glass). Both mechanical and optical behaviors were studied through several models subjected to uniaxial and biaxial states of stress. The discussion of the results and of the experimental methods used leaded to the conclusion that this method reached good resolution – of a maximum of 20 per cent – in spite of difficulties reached in interpreting the optical response this is a function of both material’s transparency and residual elastic stresses.