CHEMICAL WATERMARKING OF PAPER
THE NONDESTRUCTIVE identification methods that distinguish between traditional and chemical watermarks are:
- Under short-wave ultraviolet illumination (180–280nm) chemical watermarks do not fluoresce and will appear dark, opaque, and distinct on papers that contain fluorescent brighteners. Long-wave ultraviolet illumination (300–400nm) causes chemical watermarks to fluoresce opaque white, thereby revealing them on unbrightened papers. Traditional watermarks will be indistinguishable from the paper under either ultraviolet source. Protective yellow glasses must be worn when using ultraviolet sources.
- Beta (radioactive Carbon 14) and Grenz (4–10 kV) radiography records differences in paper density, including fiber distribution, wire patterns, and traditional watermarks, but will not record chemical watermarks.
- Visual identification can sometimes be made under the microscope using a raking reflectance light source. A dark blue filter placed over the light source can enhance this technique. The chemical watermarks appeared slightly more matte, opaque, and dark when viewed with the blue light.
- A positive destructive test can be achieved through the use of numerous organic solvents. A small localized application of organic solvent will quickly result in a visual loss of the watermark. It is not yet known whether this change in translucency can be reversed, so destructive testing should be considered only as a final testing option.
9.2 TREATMENT EFFECTS
- The various erasers tested did not seem to have any adverse effects on the watermarks. Groomstick, a natural rubber product, left a spot of slight discoloration on the paper after eight weeks of direct contact.
- The chemically watermarked designs were altered on contact with all of the organic solvents chosen. However, the watermarks appear crisp and unaltered when viewed under short-wave ultraviolet illumination. This contradiction suggests that watermark components that provide translucency of the mark were moved by the application of organic solvents; components that absorbed short-wave ultraviolet radiation were unaffected by organic solvent application. Before the conservator undertakes local treatments with organic solvents, a paper with a chemically watermarked design should be carefully examined and tested to determine whether the laid and chain lines were also chemically produced.
- Washing in neutral aqueous and alkaline solutions seemed to slightly diffuse the chemical watermarks into the paper. The effect of diffusion seems aggravated by the increase in duration of the immersion. A component of the paper fillers, brighteners, or chemical watermarks seemed to dissolve and redistribute over the papers, shielding the watermarks from the ultraviolet source.
- The effects of bleaches and bleach neutralizers gave varying results. Chlorine dioxide and sodium hypochlorite bleaches did not seem to disturb the chemical watermark in any of the three samples. Sodium borohydride only slightly lightened the watermark but did have adverse effects on the paper.
Experimentation often produces more questions than answers. This project is no exception, and the results of the tests are still being considered. Additional in-depth experiments are needed to better understand the characteristics and conservation treatment limitations of chemical watermarks.
GEORGE BOECK, formerly of the Dard Hunter Paper Museum at the Institute of Paper Chemistry in Appleton, Wisconsin (now the Institute of Paper Science and Technology, Inc., Atlanta, Georgia), brought the watermarks to my attention during the summer of 1988. Ken Carlson of the Fox River Paper Company, Appleton, Wisconsin, generously donated the sample papers and courteously answered questions concerning this technology.
I am grateful to Walter J. Rantanen, fiber specialist at the Institute of Paper Science and Technology, Inc., for sharing his expertise and enthusiasm about this material. The SEM analysis performed by Mary Block, fiber specialist at the Institute of Paper Science and Technology, Inc., is greatly appreciated. I am thankful to the faculty of the State University College at Buffalo's Art Conservation Department, specifically Chris Tahk, Cathy Baker, and Dan Kushel for offering their advice, encouragement, and help with the innumerable aspects of this research. Finally, I am enormously indebted to Marian Peck Dirda of the Library of Congress, Washington, D.C., for her insightful criticism and editing.
This project was partially supported by a spring 1989 student award from the Office of the Dean of the Faculty of Arts and Humanities, State University of New York College at Buffalo. The work was completed as partial fulfillment of a master's degree in art conservation. The samples and documentation are on file at the Art Conservation Department, State University College of New York at Buffalo, New York.