Description of step exposures
Step exposures are a means of determing the optimum exposure time. Correct exposure time depends on the characteristics of the photo emulsion or film, the mesh, overall thickness, the light source, and the distance between the lamp and the material to be exposed.
Underexposed stencils do not harden all the way through; photo emulsion on the squeegee side is washed away during development. A smudged photosensitive layer is a sure sign of underexposure. With inadequate rinsing, some of the dissolved photo emulsion sticks in the open parts of the stencil. A barely visible scum is left behind after drying, which impedes ink flow during printing.
Underexposed stencils also have poor resistance to solvents, printing inks and mechanical wear. The stencil is also difficult to reclaim afterwards.
Overexposed stencils may suffer from reduced resolution; this is especially noticeable with white mesh.