Reflection factors of photographic papers

Reflection factor curves for gaslight photographic papers with matt and glossy surfaces have been obtained for a fixed direction of view of 30°, this direction lying in the plane of incidence. The papers give not only a specular peak, but also a "throwback" peak whose maximum occurs when the directions of incidence and view coincide. The height of the throwback peak is related to the reflection factor of the paper at the angle of the throwback peak by a linear law. By considering in turn the different components of the photographic paper, the throwback peak has been shown to have its origin in the baryta layer. The complete reflection factor surfaces for a fixed direction of view of 30° have been built up for two pieces of matt surface paper from the reflection factor curves in different planes. As various liquid suspensions also give a throwback peak, the peak may have its origin in some kind of scattering effect.