Frequently the emulsion will break down near the thin side of the frame when liquid emulsion is used whereas a film product will not break down. If the stencil breaks down, production time is lost repairing the screen, and mis-prints may have been created. The cost of these problems can be measured by the profit that could have been earned printing during the time production was lost repairing the screen. Film products work well with gray positives, that is, images created by computer or photocopy machine on translucent paper. Typically these images are not dense black like positives from a camera.
Light leaks through the image during exposure.
Over exposure can make wash out difficult. An exposure calculator, which is nothing more than a specialized film positive, allows determining how much light is required to expose the stencil material. Thicker film stencils require more light exposure. The exposure calculators are offered by the emulsion manufacturers and sold through their distributors. Once the time required to expose film is determined with the exposure calculator, then every time that stencil thickness is selected the screen printer will know how long the light must be on to avoid over or under exposure.