By Tania Passafiume and Jennifer Roger
Depending on conditions, the rates of deterioration of the materials that make up a daguerreotype package (e.g., copper, silver, paper, brass, leather, velvet, silk and glass) can vary substantially. One of the most common problems found by conservators is glass deterioration.
Glass deterioration often makes the daguerreotype appear dull and hazy. This does not necessarily mean that the plate itself has deteriorated. A number of the daguerreotypes from the Library and Archives Canada (LAC) collection that were prepared and treated for exhibition showed distinct signs of glass deterioration
Glass deterioration can occur as a result of fluctuations in either temperature or humidity. There are a couple of ways in which this type of degradation can manifest itself. One is cracking, which is when tiny hairline cracks appear on the surface of the glass. The other is chemical decomposition, which affects older glass with a higher concentration of sodium oxide, causing the glass to appear hazy or cloudy.
Keeping the original glass of a daguerreotype is always encouraged, and in cases where the glass is in an early stage of deterioration, e.g., it appears hazy or foggy, it can possibly be cleaned and reused. Treating this type of deterioration is relatively straightforward: the glass is removed, cleaned with distilled water and a neutral soap, rinsed with ethanol, then left to air dry. When placed back onto the daguerreotype, the plate will immediately appear brighter and clearer.
When glass is at a more advanced stage of decomposition, alkaline droplets form on the surface facing the bare daguerreotype plate. Glass affected by this type of deterioration is called “weeping” glass, as the glass or the images can appear to be crying. The droplets could fall from the glass and land on the surface of the bare plate, affecting its stability. To avoid jeopardizing the plate’s stability, the deteriorated, “weeping” glass should be removed and replaced with borosilicate glass, a very stable modern-day glass.
In the event that the glass cannot be replaced immediately, a simple solution would be to store the daguerreotype with the image side down, thus protecting the plate within the package.
Watch the video: An inside look at daguerreotype conservation
For more information about the daguerreotype collection at Library and Archives Canada, check out our Flickr album or listen to the podcast, Mirrors with Memory. To learn more about LAC’s conservation projects, visit our “Conservation Wednesdays” feature on our Facebook page!
Tania Passafiume is the Head Conservator of Photographic Materials in the Collection Management Division of Library and Archives Canada.
Jennifer Roger is a Curator in the Exhibition and Online Content Division at Library and Archives Canada.