(Photographic Materials) Blue Pigment Inclusions in Salted Paper Prints by Lisa Barro and Silvia Centeno


In her Wednesday afternoon session, Lisa spoke about blue pigments in the paper substrate of salted paper photographs. The thematic lighting set the mood...

A conference room with blue-colored ambient lighting
The conference room was thematically lit for a talk on blue pigments.

Blue pigments were often added during the manufacture of white paper as an optical brightening agent. Lisa emphasized the significance of pigments as materials that can convey historical and art historical information, and the potential information that could be gained by studying blue pigments in photographic papers. Based on her own recent experiences with examination of salted paper photographs, she suggested that material characterization of photographs on paper should include checking for blue pigments.

Lisa began looking into blue pigments when she discovered blue particles in the salted paper prints of Giacomo Caneva. She noted that the blue pigment consisted of very small round particles which were very unlike the glassy fractured particles of smalt that have been better documented in salted paper photographs, such as those by William Henry Fox Talbot. Silvia and Lisa used Raman spectroscopy to identify the small round particles in the Caneva photographs as synthetic ultramarine. With the identification of synthetic ultramarine came the realization there may be two blue pigments common to salted paper photographs – smalt and ultramarine – that could be used to generate more nuanced material characterizations and provenance studies.

Lisa suggested a few additional ways the blue pigments might be informative. Alum size interacts with ultramarine, but starch size does not. Alum sized paper was common in England, while starch sized paper was common in France; perhaps there is a correlation between country of manufacture and the pigments used. There may also be implications for preservation, a possibility that was first raised by Thomas Sutton in 1853. He believed the sulfur component of ultramarine could cause fading of salted paper photographs. Lisa wondered, could that be true?

Lisa concluded by again emphasizing the need for better documentation of blue pigments in photographic papers. There are not many published sources on the use of ultramarine pigment in paper of any kind, although she cited one on natural ultramarine in Indian manuscript paper (Craigen W. Bowen, “Close Looking: Notes on Media and Technique,” in Mind, Heart, and Hand: Persian, Turkish, and Indian Drawings from the Stuart Cary Welch Collection, 2004).

Lisa provided compelling reasons for why we should all pay a little more attention to any blue particles we see in the photographs under our microscopes.  As a final note - she is particularly interested in examining samples of Canson d’Annonay paper, reported to have been Gustave Le Gray’s favorite paper. Let her know if you have any!