- Squeegee side of screen feels slimy. This is a sure sign the screen is underexposed. The slime is actually unexposed emulsion. If it is not completely rinsed off, it can dry in the image areas and block the ink. This is called “scum”.
- Stencil peeling away from mesh, particularly with capillary film. Stencil exposure occurs progressively from the substrate side into the squeegee side. Underexposing the stencil leaves the emulsion on the squeegee side of the mesh soft where it's literally washed away during development. If enough of this emulsion is washed away, the direct emulsion can actually peel away from the mesh. With capillary film, the fragile interface of stencil to thread can be quickly compromised when the stencil is not fully hardened.
- Stencil pinholes. If you see a lot of them during washout, underexposure is the leading cause.
- Half tone dots easily rinse off the mesh. Most dots should remain attached to the mesh during washout, when the correct mesh count is matched to line count.
- Sawtoothing- irregular edge definition. This is caused by too much emulsion washing away due to the softened emulsion
Check that your film is dark enough and that your exposure time is long enough. An exposure calculator will help to determine the appropriate time necessary.