Developing a Watermark Capture Process

Our first experiments to capture watermarks were in 2018 by request of Conservation. They had a page with a handprint left over from the papermaking process they wished to capture. This item was photographed using raking light and processed for added contrast selectively, using a soft S-curve applied to the luma channel. This method works well on this particular watermark, but is not suitable for most cases where the watermark is far less visible without backlighting.

A piece of paper with a visible hand print. The contrast between the lights and darks has been exaggerated to make the handprint more visible.

Our first watermark capture

This final product was chosen after attempts at underlighting with Conservation's LED light sheet. Both color and grayscale images were taken, but it was found that aesthetically the tools we were using did not make an image as nice as one we could produce through post-processing.

Four images of our first watermark attempt. The first image shows the item lit as per our usual scanning requirements. The handprint is visible. The second image shows the item lit from underneath. The handprint is clearly visible, but the color of the paper has dramatically changed. Vertical stripes of light corresponding to the placement of the LEDs are visible. The third image is a version of the seond image in grayscale. This makes the stripes from the LEDs even more visible. The final image is the chosen product for this experiment, as seen above.

Four variants on our first watermark attempt. The first is lit as per our usual practices. The second is underlit. The third is a grayscale version of the second. The final image is the chosen varient.

A front-facing view of the 413 copy stand. It is a flat table with two aluminum stands coming off the back at 45 degrees and a central vertical column in the center of the back. The aluminum stands hold two LED lights facing in to the table. There is a medium-format camera mounted on the column pointing down at the tabletop. There is a book strapped to the cradle underneath the camera.

The 413 copy stand in use for book digitization.

Our 413 lab is equipped with a reprographic copy stand, primarily used for capturing book and flat-paper items. This station was chosen for the Allingham project and was adapted for the watermark capture process.

From a previous project, we have a table designed for capturing photographic negatives and other transmissive materials. When we tested it with its light box, we found that the underlighting was too strong, obscuring both the text and the watermark. However, by removing the legs of the table, we were able to attatch it to the modular top of the copystand to increase the distance from the light source.

A square table made of black aluminum and wood. It has four legs, and there is an empty space in the center of the table. There are two rubberized knobs on the end nearest the camera, and two low grips on the side away from the camera.

The transmissive table.

A square table made of black aluminum and wood. The four legs have been removed, and there is an empty space in the center of the table. There are two rubberized knobs on the end farthest the camera, and two low grips on the side near the camera. Nest to the table is one of the removed legs and a set of hex keys.

The transmissive table without legs.

An image of the 413 copy stand from the side. The tabletop has been removed, showing the empty space below the top, one of the lights, and the center column. A woman in black wearing a dust mask is cleaning the copy stand with a swiffer duster.

Copy stand with top removed

Before the new top was installed, we removed one of the copy stand LED lights and placed it underneath the tabletop to provide underlighting. With this light on its lowest setting, the remaining overhead light was set to its maximum output. This lighting setup allowed for capture of the watermark with minimal alteration to the tone of the paper and legibility of the text.

Installing underlighting

After some experimentation, we opted to use plexiglass as a surface for shooting the letters. Regular glass transmitted the light too regularly, allowing the arrangement of the LEDs within the light to be visibile on the letter iteself. The plexiglass, however, helped to diffuse the light coming from beneath creating a much more even image.

The copy stand with the transparency top installed. One light has been removed from its stand and is underneath the top. The other remains in position. Both are lit.

The copy stand with transparency top and plexiglass.

With our setup complete, we were now ready to begin shooting the watermarks.

An engraving of William Allingham

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Digitizing Watermarks in the William Allingham Collection

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Capturing Watermarks