This makes it particularly challenging to conserve egg tempera paintings, as well. Conservators must use an especially light touch, since the works are not as resistant to cleaning as oil paintings. “Egg tempera is rather vulnerable,” Modestini warns, “and one has to be much more careful not to damage the paint film.”
Albumen photographs, meanwhile, are similarly susceptible to degradation because the egg white paper coating is more permeable than processes that came into vogue later, such as gelatin. Though the process was immediately popular because it offered sharper images with greater tonality than its predecessor (the salted paper print), albumen proteins are sensitive to changes in temperature and humidity.
“They knew there were issues [with albumen prints] from the start,” Kaplan says. The prints tended to yellow more easily in the white highlight areas, and networks of fine cracks would develop within only a few years. Manufacturers tried to address these problems early on, adding citric acid to the coating as a preservative. But eventually the albumen process was abandoned in favor of the silver gelatin print, which could produce glossier images and was more durable.
They were also, Kaplan surmises, cheaper to manufacture. “You didn’t have to keep a supply of chickens on your farm to produce silver gelatin photos,” Kaplan says.