The Opacity Tester is used to determine opitcal characteristics of plastics including colour, clarity, general appeareance and more directly measurable properties, such as index of refrection.

Most resin by nature are clear and transperant. They can be coloured by dyes and will become opaque as pigment or fillers are added. Polystyrene and poly (methyI methacrylate) are well know for their optical clarity, which even exceeds, that of most glass. Optical clarity is measurement of light transmitting ability of the material. It depends,among other things, on the length of the light path, which can be quantitatively expressed.