Drag your pointer across the image to compare the original transmitted light photograph with the same image after a single Photoshop processing step to minimize the obscuring pen and ink inscriptions on the paper (Note: Inscriptions were only on the right half of the paper)
The Tissandier Collection was purchased by the Library of Congress in 1930 and contains approximately eight thousand items. It was collected by the French brothers Albert (1839-1906) and Gaston (1843-1899) Tissandier and documents the early history of aeronautics with an emphasis on balloon flight in France and other European countries.
The collection includes original manuscripts from the brothers Joseph (1740-1810) and Étienne (1745-1799) Montgolfier, of the prosperous southeastern French papermaking Montgolfier family. In the early 1780s, Joseph and Étienne invented the hot-air balloon using their family mill's paper to line the cloth fabric of the balloon. (Coincidentally, the Library of Congress holds a blank sheet of Montgolfier paper with an elaborate watermark that was likely designed to commemorate the 100th anniversary of this first flight.)
Technical examination of the papers in the Tissandier Collection produced a record of the various papers and watermarks and resulted in the development of a simple method -- using Adobe Photoshop -- to produce clearer images of watermarks obtained by transmitted light photography, which are often obscured by the inscriptions on the paper.
Common methods to date for capturing watermarks include transmitted light photography, raking light photography, electron radiography, beta radiography, multispectral imaging, tracing by hand, and rubbing. These techniques have advantages and disadvantages, summarized in the table below.
| Method | Advantages and Disadvantages |
|---|---|
| Rubbing | Advantages: Direct contact of the watermarked paper with the tracing paper produces a 1:1 scaled image; requires no special equipment; extremely low cost Disadvantages: Poor image resolution; fallibility of the human hand |
| Tracing | Advantages: Direct contact of the watermarked paper with the tracing paper produces a 1:1 scaled image; requires only a lightbox; extremely low cost Disadvantages: Tracing pressure can emboss the original paper; fallibility of the human eye and hand; media obscures watermark image |
| Transmitted Light Photography | Advantages: Image obtained with a standard camera and lightbox; low cost; transmitted light photography is a standard form of conservation and examination documentation Disadvantages: Media obscures watermark image; poor contrast with thick papers |
| Low Energy Radiography | Advantages: Direct contact of the watermarked paper with the film produces a 1:1 scaled image; clear, high contrast image produced with no or minimal interference by media Disadvantages: Safety restrictions on acquiring, maintaining, and using the radiation source; requires special equipment and training; cost of equipment |
| Multispectral Imaging | Advantages: Image capture under different wavebands of radiation can reveal more information; more source images enables more manipulation that can increase the legibility of the watermark Disadvantages: Requires special equipment and training; cost of equipment |
The Photoshop method described here leverages the existing low-tech, low-cost, and widely used technique of transmitted light photography to document watermarks. Two simple manipulations of a transmitted light digital image of a watermark drastically enhance watermark legibility by: (1) substituting the pixels representing dark media inscriptions with a midtone color, and (2) maximizing contrast in the resulting image to render the watermark light and the paper dark.
The main advantages of this method for enhancing watermark legibility are:
- Low cost of necessary equipment and software
- Low tech, but still a photomechanical capture (instead of hand-capture) of the watermark
- Easy-to-learn and simple software processing steps
- Increased usefulness of/additional data from an already extant image, i.e., the transmitted light image
Like all other techniques for capturing watermarks, this method has disadvantages, the most significant of which is that the easiest Photoshop processing and best results are limited to papers bearing one kind of media that is evenly applied; a watercolor painting, for example, with many colors and color densities, would be more difficult and more time consuming to process in the first step. Nevertheless, the images on the next page illustrate that Photoshop is a readily available and powerful tool for aiding the study of watermarks.
