Understanding Frédéric Flachéron’s Paper Negative Process through Experimentation and Specular Reflection FTIR Analysis

Cultural heritage objects present a special set of challenges for chemical analysis. Often micro-sampling or even contacting the object is deemed an unacceptable risk to the object. This study examined if specular reflection FTIR, a non-sampling and non-contact analytical technique, can provide insight into chemical composition of the layered coatings on Frédéric Flachéron’s paper negatives (1848–1852) in the Harrison D. Horblit Collection of Early Photography, in Houghton Library, at Harvard University. Specular reflection FTIR data confirmed the identification of beeswax and sandarac as the transparentizing media on Flachéron’s paper negatives, as previously published by Lee Ann Daffner. However, specular reflection FTIR analysis also indicated that some negatives had additional localized coatings of orange shellac in specific areas of the images. To understand why Flachéron retouched his negatives with orange shellac, modern experimental replications of the paper negative process were performed. Through modern experimentation with the paper negative technique, it was found that Flachéron’s coatings of shellac served as an integral part of his image-altering technique. The color of the orange shellac subtly alters contrast and density, but it does not mask an area the way an opaque watercolor or highly pigmented paint might. The fine adjustments to the negatives with orange shellac were an attempt to perfect the contrast in the print, and better render depth and detail. These discoveries add to a growing body of recent research that points to the historic and art historic importance of negatives and coatings in photography. The specificity with which specular reflection FTIR was able to nondestructively identify the chemical composition of the local coating, and specifically target the analysis on the areas in which it appeared, allowed for an understanding of Flachéron’s use of local coatings as a retouching method rather than a protective coating.