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Photographs: Early Ungilded Daguerreotype Images
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Background: The Library of Congress’ Prints and Photographs Division has over 725 daguerreotypes. The daguerreotype photographic process, introduced in France in 1839, creates a highly detailed image on either a silver plate or a sheet of copper plated with a thin coat of silver, without the use of a negative. The plate is cleaned and polished until the surface looks like a mirror, then sensitized (either once or, in the case of some copper-silver plates, twice) in a closed box over iodine and/or bromine. After exposure to light, the plate is developed over mercury vapor until an image appears. To fix the image, the plate is immersed either in a solution of sodium thiosulfate or sodium chloride.
In 1841, daguerreotypists began toning (‘gilding’) plates with gold chloride, which added greatly to image stability by adhering the particles to the plate, and improving image contrast. Some research has been done on the preservation and stability of gilded daguerreotypes and methods have been developed to clean them. However, no comprehensive study on the preservation of ungilded daguerreotypes exists. Furthermore, there are no known methods to remove glass deterioration products, biological materials, or tarnish, from the surface of ungilded plates, all of which are potential problems and can greatly harm and disfigure the image.
Project Description: The Library has designed a project to:
- Define standard best practices of analysis for ungilded daguerreotypes
- Thoroughly document its collection of ungilded daguerreotypes, including composition and treatment history
- Design optimal housing and storage conditions for the plates
- Add to the overall body of knowledge regarding ungilded daguerreotypes
Questions to be addressed include:
- What is the nature of the tarnish(es) and other blemishes affecting the plates?
- What are the optimum storage conditions to slow or stop the tarnish and the deterioration of original housing components?
- Are there acceptable methods that can be adopted to clean ungilded plates?
For this preliminary study, plates have been manufactured to historic standards with identical grayscales. By subjecting the plates to various conditions scientists and conservators can compare particle density, shape, and distribution changes to ascertain the effects of various manufacturing techniques and subsequent treatments.
Before carrying out tests on vintage collection plates, various analytical techniques will be analyzed on a subset of manufactured controls by optical microscopy, X-ray fluorescence (XRF), Environmental Scanning Electron Microscopy (ESEM) and coupled Energy-dispersive X-Ray (EDX), etc. to evaluate the efficacy and safety of each method, and develop a set of best practices for studying the plates. Before and after high-resolution baseline images will be generated using hyperspectral imaging (HSI) techniques.