PRESERVATION OF 19TH-CENTURY NEGATIVES IN THE NATIONAL ARCHIVES
1.. An original petition of Matthew B. Brady, in the custody of the National Archives, requests that Congress purchase his collection of Civil War photographs. In this document, which bears his signature, Brady's given name is spelled “Matthew” (with a double “t”). While his given name is customarily spelled with only one "t," it seems reasonable in this article to follow the spelling in Brady's petition.
2.. Coe and Haworth-Booth also describe albumen negatives as “creamy or milky” in color. When they usually appear reddish brown in hue.
3.. The term “emulsion coating” seems to describe the varnish layer. However, gelatin plates may be varnished with uneven coatings as well.
4.. This description may be considered accurate from a technical standpoint. however, it may be misleading to those unfamiliar with collodion collections and the process by which they are made. The term “flow marks” and “varing thickness” imply a three dimensionality associated with the collodion layer. The three-dimensional surface character of collodion plates observed by the naked eye is primarily a result of the thicker varnish layer.
5.. To achieve the desired three-dimensional effect, the position of two camera-generated stereo images must be laterally swapped. In production shops, stereo plates were often cut in half and the positions swapped and mounted with gummed paper tape to a secondary glass support to facilitate contact printing. This single procedure eliminated the need to trim numerous prints before mounting.
6.. The secondary effect described by Brems is apparently more relevant to collodion negative deterioration than the primary effect seen in the degradation of cellulose nitrate-based negatives.
7.. The use of organic solvents, such as Kodak Film Cleaner (1,1,1 trichloroethane) on collodion plates is not recommended. The varnish layer, as well as the underlying collodion binder layer, are soluble in most organic solvents. Treatment with organic solvents may result in loss of image.
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CONSTANCE MCCABE received her MFA in 1982 at Rochester Institute of Technology in the School of Photographic Arts and Sciences' Museum Practice Program and served internships with the George Eastman House and the Image Permanence Institute. At the time of writing this article, she was senior photograph conservator at the National Archives in Washington, D.C. She is currently working as a photograph preservation consultant and is president of Photo Preservation Services, Inc., a negative duplication service, Address: 409 Constitution Avenue, N.E. #4, Washington, D.C. 20002.