Thursday, June 27, 2013

UV Exposure Box for Polymer Plates

Once I had multiple letterpress printers and learned how to letterpress with polymer  the missing element was a way to expose plates myself so I can be more spontaneous. I've done research for years and almost bought an exposure unit but couldn't decide which kind. In the end my DIY urge took over. I always think, "Why, I could make that!"  Sometimes I'm too optimistic--we won't talk about the vacuum frame I made some years ago to use with my previous exposure unit made of a Home Depot work light with the UV protection screen removed mounted on a discarded darkroom easel. The worklight did emit UV but not strong enough so although I sometimes succeeded it was more luck than reliability.  Also heat would really build up and that didn't seem good for the plate material.   Now I was ready to do a more professional attempt at an exposure unit.

My hopes were to use it for exposing Solarplate, letterpress plates like the ones from Boxcar Press, and Imagon which was my first love. Advice varies from guru to guru. Keith Howard says you HAVE to have a point light source and that fluorescent bounces all around and I guess gets under your negative/transparency.   I can't afford those lights and they scare me a little bit so on to Plan B. It seems that many people are doing well with black lights. In Dan Weldon's book on Solarplate, Printmaking in the Sun, he gives instructions for making a box but when he gets to the step of wiring it he says to find an electrician--no way I want to pay for that.  Nevertheless, I decided to forge ahead.

Home Depot was the first stop where we got the MDF for the box and had it cut to order (thanks to the nice man who  so carefully cut the pieces).   In the lighting department I wandered around feeling discouraged until I came across some fluorescent bulb units that said they could be plugged into each other in a continuous line and at the end would be a regular plug--hooray!  I think they were meant for undercounter lighting.  They were about the size (18")  I wanted for my box so I bought 8 and later went back for 2 more to make the light source wider . Then I discovered that black lights didn't come in this size at home depot. I hit the internet--it took a long time to find the right bulbs.    Bulb Town was my hero. I learned a lot about fluorescents and their obscure naming codes.  Meanwhile I built the box and waited impatiently for the black light bulbs. I painted the interior of the box black to reduce the light bouncing around. I worried that there was some other type of fluorescent black lights that I should have gotten rather than the  the straight "black light" ones I chose.

With the bulbs installed the next step was to expose some test strips to a Stouffer scale negative and see what would happen. I wasn't completely clear on what I was going for--I only knew the Stouffer value for one of my plate materials so I used that as my guide. I figured the thicker material would take longer to expose and my test strips seemed to agree.  So my exposure box worked!!

  I began to realize how valuable a timer that controls the lights would be. So far I haven't found such a device in my price range (cheap).   I don't entirely trust my test strips as I 'm not so good at timing precisely and I like to go do something else rather that stand there twiddling my thumbs.  With a timer I could relax and know it would turn off after the right amount of time.  I think the slim line bulbs put out less light so exposure takes longer than units I read about. This is ok because, unlike the work light, heat doesn't build up during a longer exposure.

At first I put the plate right on the counter and the lights were the distance of the height of the box away from the plate.  Later on I decided to put the plates closer by building up a platform within the box.  I had to cut a flap out of the side of the box so I don't have to lift the entire box.  I put two hinges on the flap so I can lift the flap, insert the plate, and secure it with a turnkey.

I'm sure professionally exposed plates are better than what I can make, but as an artist and amateur printer of books, I'm quite happy  using my homemade plates.  As an impatient  person who sometimes doesn't plan very far ahead this is the perfect system for me.  For special projects I will still rely on Boxcar Press to make my plates--they do an awesome and perfect job.

It's Boxcar Press who sell the unexposed plate material I use and the excellent adhesive sheets that are easy to attach.  I make negatives with my laser  or inkjet printer on transparency films made for those printers.  In order to get a proper density of black I print twice and carefully align and  tape the two transparencies together.   For exposure I use a photographic contact printing device  or  sometimes I make a sandwich of glass and a backing board with  the negative above the plate and either black felt or black funfoam under the plate.

 I have experimented with using a space bag as a DIY vacuum frame as shown by Cape Fear Press in their  video  My space bags have logos all over them but one day I realized that the simple solution is to have the back of the bag face up.  I haven't scientifically experimented to see if there is a difference in the two methods of exposure "frame".

Washing out the plate is a subject covered in various places on the internet.  I bought one of the expensive brushes sold by Boxcar and I highly recommend it.  I think exposure and washing out should have a separate post which I will have to work on.   I have lots of pictures of this uv exposure which I hope to add to this post soon.

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