Optical brighteners (i.e., fluorescent dyes that absorb UV radiation and re-emit visible light in the blue region of the spectrum) have been used in all layers of the photographic paper--paper base, baryta layer, undercoating, emulsion, or protective layer.  The optical brightener, a compound that absorbs the UV radiation and re-emits it in the blue end of the visible spectrum, helps adjust for any dullness or yellow color that may be retained by the paper after processing.  The inclusion of optical brighteners in the black and white photographic papers creates concerns for those responsible for the care and exhibition of these artifacts.  The UV wavelengths of light are required to give the photographic papers the brightened white appearance. However, these same UV wavelengths can be potentially damaging to the long term stability of the optical brightener  by  causing photobleaching of the dye and fading of the chromophore. Therefore, this study has focused on the appearance changes from the optical brightener as well as the long term stability of the optical brightener exposed to UV light.

In this study, we have evaluated forty five historic photographic papers, representing twelve manufacturers and ranging in date from 1956-2006 provided by Paul Messier of Paul Messier LLC, Conservation of Photographs, Works on Paper, and Electronic Media.

Research focuses include:

• Determining the impact of the optical brighteners on the appearance of the photographic papers when illuminated with near UV-radiation
• Evaluating the light sensitivity of the optical brighteners on the photographic papers

The photographic papers studied were usually relatively white in their unbrightened state and changed only slightly in appearance to more white or very blue-white upon activation of their optical brightener.  One third of the papers did  experienced large appearance changes (> DE of 5.5) and exclusion of UV radiation from the illuminating light source for these papers may cause a noticeable change in the papers' appearance.

In evaluating the light sensitivity of the optical brighteners it was determined that the overall color change was due only in part to loss of the optical brightener and also was due to bleaching or yellowing of the paper substrate and fading of a chromophore at 570 nm.  While there was optical brightener loss in all 45 samples from exposure to UV radiation it is important to note that the samples were not very sensitive to the light exposure and were judged to have lightfastness ratings better than Blue Wool 3.

For more information:
        Connors-Rowe et al. JAIC, 46 (2007): 199-213. (pdf)

Top of page