The technique bypasses the complicated and traditional method of machining a brass die and matrix between which the screening is pressed to achieve an articulated surface. The germ of the idea originated from reading Hand Papermaking's Summer 1994 issue (volume 9, number 1) which featured an interview with Neal Bonham. Bonham was creating innovative decorated papers that synthesized watermarks and multiple colored washes of finely beaten cotton pulp, but the salient feature was that he used a thin layer of PU foam as a mould surface. Bonham burned or melted the PU foam with a wood-burning knife to fashion a light-and-shade watermark. Computer-Driven Laser Cutter for Chiaroscuro Watermarks brian queen Close detail of the engraved foam watermark stencil. All photos courtesy of the author. Open-cell, flexible polyurethane foam is available in different pore sizes or PPI (pores per inch). Standard upholstery foam is approximately 40 PPI. This roughly corresponds to a 40-mesh woven brass screen commonly used on hand papermaking moulds. I began by experimenting with 40-PPI foam purchased from a local mattress supplier who custom cut it to ¼-inch thickness. To reduce the patterned texture of the finished sheet, I moved to a finer pore size, first 60, then 80 and finally 100 PPI. The fine pore size created a more defined watermark without noticeably slowing drainage as common sense would dictate. The process starts on the computer. I scan an image and load it into ArtCAM (a proprietary program); if it is a color image, I convert it to grayscale. The program creates a three-dimensional model, with the lighter areas of the image translated as low heights and the darker areas greater heights. Then the program converts the 3-D model into the numerical code that the laser machine uses to engrave the image in the foam. A laser is a tightly focused beam of light so powerful that it can penetrate many materials. When it cuts entirely through a material such as cloth, paper, or wood, we call this laser cutting. When the laser vaporizes only the top surface of the material, it is called laser engraving. The watermarking process uses both techniques. First the laser engraves the watermark image and then cuts through the ¼-inch-thick sheet of foam to create the outside perimeter of the foam sheet. The laser works in the same manner for both cutting and engraving; the only difference is the level of power and how it passes over the material. When engraving, the laser head moves over the material like an inkjet printer passes over a piece of paper: the laser vaporizes a very narrow swath of the material, and when it reaches the far side of the image it moves down a small amount and returns in the opposite direction, back and forth in a zigzag pattern. In addition the power of the laser increases and decreases as it traverses the image referencing the grayscale value in the original image. For instance any portion of the image that is 100% black are engraved the deepest (about 0.1 inch in depth) and these areas appear the darkest in the final watermark. Areas that are 50% gray are engraved half this amount and appear as a midtone. The laser adjusts its engraving power for every grayscale level, resulting in a continuous-tone watermark, the hallmark of a chiaroscuro watermark. When I make watermarked sheets with the engraved foam, I place it on top of an existing laid or wove papermaking mould. However since the mould is only acting as a support, I could use an eggcrate louver in place of a mould. As the foam is a ¼-inch thick, the deckle must be offset or raised by the same amount so that it does not squash the foam around the edges. I form the sheet in the usual manner including the papermaker's shake. To transfer the sheet, I place a felt on top of the newly formed sheet, followed by a board, and flip the whole assembly upside down and place it onto a table. I remove the mould, exposing the backside of the foam. Then I place a board on top of the foam and press by hand to remove excess water. The final step is to carefully peel the foam off the newly formed sheet. This method of creating light-and-shade watermarks is quick and relatively inexpensive although for reasons I have not yet discerned it does not produce the quality and definition of the best watermarks produced in Fabriano. Here are some issues that I will continue to work to resolve. I have found couching to be problematic: the foam retains water like a sponge and definition is lost as excess water refloods the newly formed sheet in the final pressing. Short fibers tend to get trapped in the foam cells and tear away from the sheet as the foam is peeled away. With watermarks, pulp preparation plays as large a role as the creation of the mould, so I plan to do more research there too. Despite these problems, I think this method of creating watermarks has great artistic potential. The ¼-inch-thick PU material is inexpensive. If the image needs some tweaking, it is a simple matter to laser engrave another piece of foam. Altering the image and laser engraving take only a few hours, then you are back at the vat

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