6. Optical Brighteners in Photographic Paper: New Methods, Data, Results

Alison Carranza, Post-baccalaureate scholar in the Yale Cultural Heritage Research and Practice Program

Optical brightening agents (OBAs) were used in papers, fibers, and textiles for decades, allowing objects to appear whiter and brighter because of ultraviolet (UV) induced fluorescence. Sources often describe these chemicals as having been introduced to the photographic paper industry in the 1950s, which has been further demonstrated through a 2005 study that qualitatively evaluated photographic paper for the presence of OBAs. These findings have been essential in photograph dating practices often implemented by conservators and other researchers. My study examined the paper samples used in the 2005 study to quantitatively analyze the presence of OBAs. This work was augmented by the LML’s color measurements of each sample in its reference collection. These spectral measurements both included and excluded incident UV allowing us to quantify UV-induced fluorescence. These data then afforded us the opportunity to compare the results of instrument-based methods and detection “by eye.” Interpreting these combined results, we can better understand our limitations for detecting OBAs and develop a more refined timeline for OBA adoption and use.