Preservation of Daguerreotypes

Photograph from Kathleen McGarvey and the Rochester Review

I knew that I wanted to write my final blog post on archival preservation of photographs; however, this is such a broad topic that I decided to narrow it down a bit and chose to focus specifically on the preservation of daguerreotypes. The preservation of this particular photographic format is an interesting and important issue to consider for several reasons. The daguerreotype was predominant in the United States from about 1840 up to the Civil War, which means that daguerreotypes are among the oldest and potentially most valuable photographs in archival collections. Additionally, daguerreotypes have inherent vice; there is silver contained within them, which both causes the image to tarnish and can react in a detrimental fashion with other elements. However, perhaps the most important issue involved in the preservation of daguerreotypes is the fact that they are direct positive images, meaning that they are unique and can't be reproduced--the only way to technically "reproduce" a daguerreotype is by taking a photograph of it. If a daguerreotype image is destroyed, it is gone for good.

The daguerreotype, introduced by Louis Jacques Mandé Daguerre in 1839, is considered to be "the first fully successful and practicable photographic process" (Ritzenthaler et al. 29). Images were made by coating a copper plate with silver and heating it over iodine to create a light-sensitive silver iodide coating, then putting the plate into a camera and exposing it to light for often lengthy periods of time, sometimes up to an hour or more. The image was then developed using mercury vapors. Daguerre started out by fixing the image using common salt but in 1839 "followed the suggestion of Sir John Herschel and adopted hyposulphate of soda as the fixing agent" (Sussex PhotoHistory). Gold toning or gilding could be added to the image before washing the plate using distilled water, drying it over a flame, and encasing it for display. Largely because of this complicated and time-consuming process, daguerreotypes were surpassed in popularity by other photographic processes within a couple decades. Today, however, daguerreotypes remain fascinating and useful materials for studying the past, and as such should be preserved with care.

Photograph from Sussex PhotoHistory

The preservation of daguerreotypes is a complicated issue largely because of the way they were created. The silver used to produce an image can cause the image to become tarnished over time (although the practice of sealing the plate in an enclosure does help prevent the image from tarnishing). Ritzenthaler et al. note that in the past, photographic conservation literature recommended that daguerreotypes be cleaned and tarnish removed using certain solvents, such as a solution of thiourea phosphoric acid, a practice that archivists followed. However, the use of solvents was eventually found to cause "permanent spots on the image and remove...image silver" (Ritzenthaler et al. 242), and therefore the practice was discontinued. While new, less damaging cleaning methods have been developed, it is recommended that serious preservation work (in other words, anything more than supporting loose daguerreotype plates within an enclosure) be undertaken only by photograph conservators.

Several of the current processes for cleaning daguerreotypes are described on the website of Princeton University's Mudd Manuscript Library. The most common and least intensive technique is the dry clean method, which is used to maintain daguerreotypes which are in good condition. This process is also performed before any other conservation cleaning technique is undertaken. In dry cleaning the plate is cleaned "using compressed air from an ear syringe, which loosen[s] and remove[s] any debris from the surface of the plate" (Mudd Manuscript Library). The water wash technique is the second level of treatment and is used for daguerreotypes that are somewhat damaged. It involves immersing the plate into warm, deionized water and then drying it in a succession of solvents. The most intensive conservation method is the electro-clean technique. This process entails first bathing the plate in water and then immersing it in "a solution of ammonium hydroxide and deionized water, and applying a weak electric current through a thin silver bar above, but not touching" the plate, which removes the corrosion (Mudd Manuscript Library). As with water washing, the plate is then dried in a series of solvent baths.

  

Before and after photographs of a daguerreotype that has been

cleaned using the water wash technique

Princeton University Mudd Manuscript Library

Before and after photographs of a daguerreotype that has been

cleaned using the electro-clean technique

Princeton University Mudd Manuscript Library

Further important discoveries on daguerreotype preservation have been made over the past decade, prompted by the "Young America" exhibition in 2005-2006. This exhibit was organized by the George Eastman House and the International Center of Photography and featured about 160 daguerreotypes created by the well-known Boston firm Southworth & Hawes, "one of the earliest photographic studios in America" (Weigandt and Meller 1). Despite careful preparation, and seemingly well-thought-out preservation methods put in place by conservators, after the daguerreotypes had been on exhibit for only a month many of the images started to degrade, showing blemishes such as white spots, iridescent halos, and blisters. Some images also formed a "disfiguring bloom or white haze" (Weigandt and Meller 7). Aware of the endangered state of the daguerreotypes as direct positive images, the Eastman House took them off display in 2006 to avoid further damage.

White spots and halos that formed on a daguerreotype

displayed during the "Young America" exhibition

Photograph from Wiegandt and Meller

Meanwhile, Eastman House conservator Ralph Wiegandt set to work to figure out what had gone wrong during the exhibition. Working with physicist Nicholas Bigelow from the University of Rochester, Wiegandt soon discovered that because the plates were created in Boston and exposed to the city's salty air, "chlorides had permeated the plates" (Grushkin). When spotlights were focused on the plates during the exhibit they were essentially re-exposed, causing silver chloride crystals to form and cloud over the image.

While in this particular case the damage came from the salty sea air, conservators soon found that there is potential for damage to daguerreotypes created anywhere and in any conditions. Wiegandt and Patrick Ravines of Buffalo State University discovered that "when [daguerreotypes] were first exposed...the silver-mercury crystals drew silver from under the plates' surface," which caused small voids to form just below the surface--this is what is known as the Kirkendall effect (Grushkin). Contaminants had seeped into these voids over the more than 150 years since the daguerreotypes' creation, leading to the adverse reactions when the exhibition spotlights shone on them. Furthermore, Weigandt's team has recently discovered that the silver plate of a daguerreotype is actually "a biologically active surface," with "small colonies of fungi" growing inside it (McGarvey 44). The fungi interacts with the plate's metals, and it is believed eventually sends the metals to the plate's surface as metallic nodules.

These discoveries emphasizes the danger of putting daguerreotypes on display. According to Grushkin, another planned exhibition--this one by the Yale Center for British Art--has been postponed until a safe way to display daguerreotypes has been established. This is something that will most likely happen using the complicated science of nanotechnology; essentially Bigelow says they are trying to "learn how to control the Kirkendall effect to create a single, uniform hole in a metal particle" (Grushkin).

One final issue to think about is that of copying a daguerreotype, as this is the one way to solve the issue of reproducing the direct positive and "preserving" at least the image. The mirror-like image on the plate may make it difficult to get a good copy image; Ritzenthaler et al. suggest "hanging a black velvet or cardboard screen in front of the camera with a hole cut in it to fit the lens barrel," which helps eliminate reflections (Ritzenthaler et al. 370). Digitization of daguerreotype images is also an option, although it is generally done using copy images or negatives rather than by scanning the plates themselves; this is what the Library of Congress did when digitizing their daguerreotype collection, as the librarians scanned copy negatives as well as color transparencies (Library of Congress). Using the copies instead of the daguerreotypes themselves helps ensure that the fragile and light-sensitive plates are further preserved for the future.

References

Grushkin, Daniel. "The Case of the Disappearing Daguerreotypes." Scientific American 32.6 (2012): 70-73.

Library of Congress. "Digitizing the Daguerreotype Collection." Retrieved from http://www.loc.gov/pictures/collection/dag/digitizing.html

McGarvey, Kathleen. "A Vanishing Past?" Rochester Review 43 (2013): 42-47.

Mudd Manuscript Library. "Conservation Techniques." Retrieved from https://www.princeton.edu/~mudd/exhibits/dags/conserve/

Ritzenthaler, Mary Lynn, Diane Vogt-O'Connor, Helena Zinkham, Brett Carnell, and Kit Peterson. Photographs: Archival Care and Management. Chicago: Society of American Archivists, 2006.

Sussex PhotoHistory. "The Daguerreotype Process." Retrieved from http://www.photohistory-sussex.co.uk/dagprocess.htm

Wiegandt, Ralph and Taina Meller. "Advances in Daguerreotype Conservation: The Conservation Program for the Exhibition , 'Young America: The Daguerreotypes of Southworth & Hawes'." In Bernier, Brenda ed. Topics in Photographic Preservation, Vol. 12. Rochester: PMG/AIC, 2007.