Re: "Solar plate"
Warning: The following is possibly way more than you ever wanted to know about polymer photogravure and traditional etching processes. :o) Photopolymer plates have been used in the commercial printing industry for many years. Printmakers have been learning that they are a less toxic way to make intaglio prints (etchings). The ones we're using for gravures (etchings), have a thin steel base with a layer of polymer on top which is photo sensitive (UV light). This polymer is water soluble UNTIL it gets exposed to UV light, which hardens it. If you expose it to UV while in contact with a film positive, the light areas of the image will harden, and the darker areas will be protected and stay soluble. The plate is then "developed" in water, washing away these areas. The plate then has low areas and high areas.... this is like a traditional copper or zinc plate which has been etched in acid baths for making etchings. After the plate has been dried and further hardened with UV exposure, it is then smeared with thick etching ink, working it into the deep areas of the plate. Then the ink is carefully polished off of the high areas (which are the lights of the image, remember?). The plate is then run through an intaglio etching press in contact with damp printmaking paper, and the ink is forced onto the paper, creating the image. The final product of this process, which we're calling a gravure, is also correctly called an etching. It is as permanent and lasting as any art process. (see Rembrandt's etchings) What I left out above is the stochastic screen part of the process. In traditional etching, it is called an "aquatint" ( from the look of "water" media.... smooth washes of tone created with watercolor). A true aquatint is produced by dusting finely ground rosin over the plate, then heating the plate to melt and fuse the particles to the plate. (we're talking about a traditional copper or zinc plate now). Those particles then resist the etching of the acid, and create a "pebbled" surface which holds ink better than a smooth surface. Now for the photo gravure process... the "aquatint" is created by using a positive film output by a high end imagesetter. it is in effect, a sheet covered with random tiny dots. This sheet of film is layered with the polymer plate and exposed to the UV light in a separate exposure from the "image" exposure. This creates the tiny raised dots of a traditional aquatint, allowing the gravure plate to hold ink better, especially in dark areas. Later today I'll try to upload a couple of photos of the etched polymer plates to my gravure blog. I hope this explains the process to those interested in what the heck we've been talking about :o) On 2/23/07, Judy Seigel <jseigel@panix.com> wrote: I'm asked offlist for a definition of solar plate. I take it for a metal plate with a soluble grain of some sort that will bite nicely when exposed to solar-type rays. But it hasn't been defined, and since it starts to seem like the holy grail, I thought it might add to the sum total of list knowledge to ask, instead of guessing.
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