If you're doing silkscreen printing using a direct photo emulsion such as Speedball Diazo Screen Printing Photo Emulsion, you can use sunlight instead of the recommended 150W clear or BBA No. 1 photoflood incandescent bulb for the photo exposure.
Using sunlight, there's no equipment to buy and no electricity used, and the exposure time is much shorter, about a minute or so. The Sun casts sharp shadows, resulting in crisp edges on your artwork. On the other hand, you can only do your exposure during the day, and the optimum exposure time can vary, depending on the time of day and the weather. We got good results with a 50-second exposure.
To determine the optimum exposure time, it's best to make a "test strip" like darkroom photographers do, as shown in the video. Place the stencil over the back side of the emulsion (the side that will face the paper or fabric being printed). Make sure the image is backwards. Cover it with glass and a piece of cardboard. Set up a board facing directly toward the sun. Place the silkscreen on the board and expose the stencil for different times, like 30-60-90-120-150-180 seconds. Rinse the emulsion in warm water, then examine the exposed regions to find the best time.
The sunlight exposure method also works well with indirect film-based photo stencil materials such as Ulano sensitized emulsions. Remember to make the exposure through the film base side, not the emulsion side.
31 июл 2015
