Greta Glaser and Maggie Wessling presented on diazotype research that was conducted in the Photograph Conservation Department at the Metropolitan Museum of Art between 1999-2012. One catalyst for this research was the 2012 display of Francesca Woodman’s Blueprint for a Temple, made up of 29 separate diazotype prints collaged together to form one image. The goal for research was to determine the best display and storage methods for the long-term preservation of diazotypes—generally through to be sensitive to deterioration caused by the environment.
As an overview of the process, Glaser described the nature of diazotypes as single layer direct positives often printed on paper supports of macerated cotton and purified wood pulp. The combination of diazo compounds with a phenol coupler and acid stabilizer produces the image, resulting in a range of possible colors, including the most common bluish-purple. Diazotypes were first marketed in the United States in the 1920s and could be used for photographic images as well as architectural drawings and other reproductions because of their ability to print with very little dimensional change from the original negative.
In order to make a thorough investigation of diazotypes and their response to the environmental, Glaser and Wessling set up light and relative humidity experiments on vintage as well as freshly processed sample papers, and Sanderson collected data on the Woodman print during installation. All experiments were calculated for roughly six months of display. Their combined spectrophotometer and microfade testing analysis produced the following summarized results:
- High humidity and light = yellowing and fading (reddening)
- All environments at or below 50% RH = same result
- In the dark, yellowing still occurs, but fading does not = greenish cast
- The rate of color change accelerates with age
- After 20 minutes of testing, samples fade between blue wool 2-3 (equivalent to approximately 1.2 million lux hours of exposure to cause noticeable fading)
Wessling summarized their conclusions from the study and highlighted the fact that environmental conditions were not controlled during analysis, which may have an affect on the data. Ultimately, diazotypes will fade with light exposure and will become yellowed in the dark, but if we can reduce the relative humidity, especially during display, the effects of exhibition will do less to alter the permanence of these photographs.