Optical Brighteners in Black-and-White Photographic Paper: Appearance and Degradation

Abstract

Forty-five optically brightened blackand- white photographic papers from 12 manufacturers spanning 1956-2006 were studied to evaluate the brightener's impact on appearance and its light sensitivity under simulated daylight conditions. The appearance tests showed both small and large changes in appearance when the optical brightener was activated by inclusion of UV in the illuminating light source. All papers showed a decrease in the Yellowness Index value upon brightener activation, indicating a change in appearance to a color that is whiter than its unbrightened version. Three papers that were originally warm white in appearance, however, remained somewhat yellow in color even with activation of their optical brighteners. All of the 45 papers experienced some optical brightener loss as a result of prolonged exposure to simulated daylight with UV wavelengths included; many also experienced other color changes such as bleaching or yellowing of the paper substrate and loss of a chromophore at 570 nm. All papers experienced color change rates similar to that of Blue Wool Standard 3 or 4 when exposed to light containing UV and would be considered moderately sensitive to light exposure.