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| Posted on 5/20/08 at 06:51 AM | |
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All lamps that emit UV energy will expose and crosslink photosensitive emulsions. This includes fluorescent tubes and especially the blacklight designed to emit UV energy. Your use of the term 'dark room' is confusing when compared to a traditional photography 'wet' dark room used to process and enlarge develop camera film. Most shops coat and store screens in the same room, but exposing in the storage room is not such a good idea. An SBQ-sensitized emulsion exposes very fast, but when you are actually coating, the water in the coating blocks UV energy which provides 'some' safety if you don't coat in a UV light safe area. This is important to remember when we insist that you dry your coating as much as possible before exposing. Any water in the stencil blocks sensitizer crosslinking. Check the safety of you storage room by coating a screen, letting it dry, then putting a coin on the stencil every 5 minutes until you get bored. When you wash out the screen, you will be able to tell you how long you can store screens in that room with exposing the stencil. Make a longer experiment by putting a coin on a stencil, on the top of your rack, that will be exposed to your safe lights, each day for a month - then wash out and develop the stencil The coins block all light and the stencil and you will get 30 different exposures.You could also tape a classic Stouffer 21 Step Gray Scale to you stencil and simulate 21 different exposure without playing with all those coins. Mark the screen with the exposure times on masking tape. Put up a sign that says you are doing an experiment and leave the coins alone! At the end of a month, you collect your coins and wash out the stencil and you have proof, no guessing. You covered position #1 on the first day, it didn't get any exposure and should wash out very fast. Progressively, you may get areas that won't wash out easily. This means the light in your room exposed them, and they won't dissolve with water and go down the drain. Count the circles and you will know how long you can store a stencil in that room and still be safe. ____________________ Richard Greaves, ASPT Ulano Corp. New York Technical Services 718-943-1338 direct | |
  
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