Description
Training video explaining how to create an Exposure Test. Created by Ulano
Transcript
The processing of Ulano emulsions is straightforward, however it may be useful to take a closer look at how to determine the proper exposure time for the stencil. For this, Ulano recommends using a "step wedge test." It's a series of five incremental exposures, all made on the same stencil. The test uses a film positive designed to show a wide variety of line thicknesses with Rubylith and Amberlith brand masking films. Use the listed approximate exposure time as a starting point. Place the coated screen with the positive taped on it into a vacuum frame and expose for fifty percent of the approximate exposure time for your light source. For the second exposure, tape the masking film in place so that it covers about one-fifth of the positive and expose again, this time for twenty-five percent of the approximate exposure time. Move the mask so that it covers two-fifths of the positive and expose again for twenty-five percent of the approximate exposure time. Continue to move the masking film over three-fifths of the positive and expose as in the last step. No covering four-fifths of the positive the final exposure is made. Of course the percentages of the exposure can be varied as desired. But the end result will still be a stencil with the approximate exposure, and two exposures above and below this approximate time. Process the stencil as before and dry. When the stencil is ready, make a print from it. After the print dries, compare it to the film positive. Usually the highest exposure consistent with resolution and adhesion requirements gives the best edge definition and greatest wear characteristics. But bear in mind that the finer the printed detail is desired, the more carefully over-exposure must be prevented. The area of best exposure will be where there is no change in the emulsion color, or where the film positives outline is no longer observable with increased exposure. Ultimately the step wedge test is valuable insurance against wasted time and materials.
