In the theaterlike darkness of the international Center of Photography in New York City, black-and-white ghosts of New England's mid-19th-century Boston Brahmins stared out from behind the glass-and-rosewood frames. These were the works of Albert Sands Southworth and Josiah Johnson Hawes, the Rembrandts of daguerreotypy—the first practical form of photography. A demure bride in white silk crepe fingered her ribbons; the stern and haughty statesman Daniel Webster glared from behind his brow. When the “Young America” exhibit opened in 2005, its 150-year-old images captured American icons at a time when the nation was transitioning from adolescence into a world power. “Each picture glows on the wall like a stone in a mood ring,” the New York Times raved in its review.
Yet after a month on exhibit, the silver plate–bound images began to degrade. White spots overtook half the portrait of a woman in a curtain-length skirt. Iridescent halos formed on abolitionist Henry Ingersoll Bowditch. Other images blistered. By the end of the two-and-a-half-month show, 25 daguerreotypes had been damaged, five of them critically.
The sudden decay created a panic within the small world of daguerreotypy. Unlike photography, where a single negative can make multiple prints, each daguerreotype is one of a kind. Once the image fades, it is forever lost. The vanishing images suggested that any daguerreotype could spontaneously crumble. Collectors feared they would lose their million-dollar collections. Conservators feared these windows into the 19th century might simply cloud over.
At the time, art conservators and daguerreotype experts had no idea what could be happening. Although most of the images had spent their existence in dark lockers at the George Eastman House International Museum of Photography and Film in Rochester, N.Y., occasional past exhibitions appeared to do no harm. This time the very act of displaying the images seemed to be destroying them as well. The Eastman House decided to take its daguerreotypes off display. The Metropolitan Museum of Art in New York City now displays only one but does so under a curtain. And the Yale Center for British Art, which had intended to stage a major exhibition of daguerreotypes, postponed it until conservators could find a safe way to put them on view.
That job fell to Ralph Wiegandt, a conservator at Eastman House who had designed the lighting and cases for the “Young America” exhibit. Wiegandt, a friendly man with shaggy hair and a tinker's inquisitiveness, found himself confronted with chemical questions beyond his conservator's expertise. “I've been a conservator for nearly 30 years, and this object stands apart,” he says. “Its entire meaning is in a molecular layer or two.” Because of the complex physics on the silver surface of daguerreotypes, the crisis called for an unlikely collaboration.
Wiegandt needed to partner with physicists. And in the course of their quest to understand the fading images, he and his partners would uncover surprising new molecular effects at the nanoscale. In doing so, the accidental relics of a 150-year-old technology may perhaps inspire the future of engineering.
Nicholas bigelow heads the physics department at the University of Rochester, located just down the road from Eastman House. He had heard about the original exhibit and in 2009 invited Wiegandt to talk about his unique problem at a physics meeting to be held in Rochester. Bigelow typically works on Bose-Einstein condensates, clouds of atoms at temperatures near absolute zero—an abstract quantum state in unimaginable conditions. Yet he was captivated by Wiegandt's talk and volunteered his services, explaining that he wanted to help with “something that has an impact on the human side of life.”
Daguerreotypes, Bigelow figured, had changed the way we see the world. Louis-Jacques-Mandé Daguerre, a Parisian artist and showman, introduced the medium in 1839, after a decade of searching for a way to fix an image on a silver plate. One day, the story goes, he accidentally broke a thermometer and absently put it in a cabinet with his silver plates. The following day he found that the mercury vapor had somehow made the image permanent. Daguerre had discovered the chemistry of image making. “What was really going on was self-assembling nanostructures,” Bigelow says. “Whether or not he meant to, he was doing nanoengineering.”
Bigelow and Wiegandt would have to reconstruct the nanoengineering that Daguerre had stumbled on (and remained oblivious to), but to do that, they first would have to do some macroengineering. On an unseasonably warm day in February, Wiegandt, Bigelow and Brian McIntyre, a microscopist at University of Rochester, knelt on the floor of the physics department, where they poked at the insides of an electron microscope with the handle of a hammer. The airlock on the vacuum chamber was being testy and required a couple of taps. When it did kick in, the computer displayed a centimeters-long rectangle of silver inside the chamber, a section of a daguerreotype Wiegandt had bought on eBay for $60 and cut into squares. On its surface was half the face of a man with shadowy eyes. “I know I cut this gentleman up. I'll take the heat for that,” Wiegandt told me.
Magnified 32 times, the man's face began to look like a 19th-century map—the corrosion by his hair an oceanic oil slick, the blisters an archipelago. Magnified 20,000 times, the silver surface looked ridged along the grain in which it was polished. Highlights such as the whites of the man's eyes revealed a hidden nanostructure that resembled tiny clusters of white eggs—uniform silver-mercury crystals whose distribution determined the image's whites and grays.
Making a daguerreotype requires three steps. First, the artist exposes silver to the vapor of iodine or bromine, both highly reactive elements called halogens. The vapor bonds to the silver to create a uniformly light-sensitive surface of silver halide. When a photographer exposes the plate, photons knock off the halides and leave pure silver. Where the image was dark, the silver halide remains. Next, the artist exposes the plate to mercury vapor. The mercury atoms bond with the pure silver and form silver-mercury crystals. As a last step, the artist washes the plate in sodium thiosulfate—film photographers call it “hypo”—which removes the halogen from the surface of the plate to leave a pure silver surface speckled with silver-mercury crystals. The bare silver reflects back as black, and the silver-mercury crystals refract light as white to create an eerie effect—the subject radiates just behind the silver's mirrorlike surface.
Because of the severely reactive silver, daguerreotypes have always been plagued by tarnish. For that reason, portrait makers would seal the plates immediately in glass cases to protect them. This method appeared to work for 150 years, until “Young America” showed them to be susceptible to light alone.
Wiegandt and bigelow were working on the problem along with conservators from the Metropolitan Museum, who found traces of chlorine in the corrosive white spots of the images. Because the plates were originally exposed to Boston's salty air, chlorides had permeated the plates. Chlorine is a halogen, like iodine, and reacts with silver. A spotlight focused on the daguerreotype at an exhibition would reexpose the plate and create silver-chloride crystals that would cloud over the original image.
Yet sea air was not the only culprit. Wiegandt and Patrick Ravines, now director of the art conservation department at Buffalo State University, found that the integrity of the daguerreotypes was also being undermined from below the surface of the plates. In collaboration with researchers at Kodak, Wiegandt's team punched a 30-micron-long rectangle through the surface of sample daguerreotypes using a focused ion beam. They then examined the layers in cross section. To their surprise, they saw 300-nanometer-wide voids just under the surface—a network of tunnels running just beneath the image.
The team believes this light-induced version results from something called the Kirkendall effect, which usually happens in alloying metals. When two different metals fuse into each other at different rates, small voids, or imperfections, form at their interface. The daguerreotype's voids must have formed when they were first exposed, when the silver-mercury crystals drew silver from under the plate's surface.
The voids could explain why some of the daguerreotypes in the exhibit showed damage. Over the course of 150 years chlorine or other contaminants might have seeped into these voids. When the pictures went on display, light may have triggered subsurface reactions between the chlorine and silver, causing the images to sprout spots from below.
Yet on a positive note, the team's discovery might help other industries. Many researchers are looking to produce uniform hollow particles for, say, drug delivery. Bigelow believes that if they learn how to control the Kirkendall effect to create a single, uniform hole in a metal particle, such a technique might be used to engineer nanocapsules for medicine.
Wiegandt cannot reverse the damage already suffered, but he can use what he has learned to protect the remaining images in the Southworth and Hawes collection. At his laboratory at Eastman House, he has built prototype frames out of aluminum and Pyrex with a valve that can seal the plates in an argon atmosphere. Argon, a noble gas, protects the daguerreotype from oxygen and contaminants in the air that can cause reactions on the silver surface. He says he has managed to bring the costs for each argon case down to $50 by using off-the-shelf materials.
He is currently in the process of producing argon cases for the museum's entire Southworth and Hawes collection. Still, that does not necessarily mean they will be going back on display. “I don't know if I'd say go ahead, let's do it,” he says. As a man who has spent the past seven years analyzing and enumerating the ways the world—from photons to fungi—can destroy the daguerreotypes' delicate surfaces, Wiegandt is understandably skittish: “I will say that daguerreotypes, whether in storage or on exhibit, should go in an argon atmosphere.”
Museumgoers may not realize what conservators never forget—every artifact, whether paint, stone or silver, has a life span. Even in pristine museum conditions, the image fades, the stone breaks, the silver nanoparticles come loose. The conservator cannot save them forever. “The two pillars of a museum are preservation and access,” Wiegandt says. Rarely have they been set so directly at odds.