| Problem |
Possible Cause |
Solution |
| Poor definition (edge sharpness) or "sawtoothing" (irregular printing edge) |
Poor contact during exposure |
Check vacuum |
| Underexposure |
Perform Step Wedge Test |
| Light scattering |
Use dyed fabric |
| Insufficient washout |
Wash from both sides |
| Poor buildup of emulsion |
Improve coating technique |
| Fabric too coarse |
Use higher mesh count |
| Stencil softness |
Improper mixing of sensitizer |
Dissolve sensitizer thoroughly, mix well with emulsion |
| Underexposure |
Perform Step Wedge Test |
| Emulsion too old |
Review storage guidelines |
| Positives "yellowed" |
Use new positives |
| Excessive hummidity |
De-humidify area, increase exposure |
| Open-area "haze" |
Positives lack density |
Use new positives |
| Poor contact during exposure |
Check vacuum |
| Light scattering |
Use dyed fabric |
| "Pre-exposure" of coated screen |
Use safelights; store coated screens in dark |
| Over / underexposure |
Perform Step Wedge Test |
| Insufficient washout |
Check washout procedure |
| Emulsion washes or peels away during washout |
Coating not uniform |
Upgrade fabric stretching and coating procedure |
| Improper mixing of sensitizer |
Dissolve sensitizer thoroughly, mix well with emulsion |
| Underexposure |
Perform Step Wedge Test |
| Improper fabric preparation |
Degrease all fabric; roughen and degrease synthetics |
| Washout temperature too high |
Washout below 100o F |
| Emulsion too old |
Review storage guidelines |
| Emulsion not dry before exposure |
Dry screen sufficiently; use screen drying cabinet |
| Excessive humidity |
Increase exposure; dehumidify shop |
| Pinholes appear after exposure and washout |
Dirt and dust settling on drying emulsion |
Dry in dust-free environment |
| Dirt on positive or contact glass |
Wipe positives; use window cleaner on contact glass |
| Pinholes / fisheyes appear before exposure |
Improper fabric preparation |
Degrease |
| Shop dirt and dust |
Housecleaning overdue |
| Wet mesh |
Dry mesh |
| Dirt and dust settling in coater or emulsion container |
Cover coater and emulsion |
| Coating stroke too fast |
Slow down; turn screen 180o after each stroke |
| Air trapped during mixing |
Allow 1-hour (minimum) for de-bubbling on mixed emulsions |
| Pinholes on-press |
Poor coating procedure |
Upgrade coating method |
| Underexposure |
Perform Step Wedge Test |
| Incompatible ink or washout solvent |
Use solvent-resistant emulsion |
| Washout solvent or solvent ink contain water |
Avoid solvent storage in large drums (condensation) |
| Frit / pigmented inks; rough substrate |
Assuming proper coating and exposure, use more abrasion resistant emulsion such as FX88 |
| Details remain closed after washout |
Coated screen stored too long |
Use freshly coated screen |
| "Pre-exposure" of coated screen |
Work under safelights; store coated screens in dark |
| Drying temperature too high |
Dry below 104oF |
| Overexposure |
Perform Step Wedge Test |
| Poor contact during exposure |
Check vacuum |
| Poor positive |
Check density |
| Light scattering |
Use dyed fabric |
| Poor light source |
Use finer mesh; use faster-exposing emulsion; upgrade light source |
| Incomplete washout |
Wash very thoroughly from both sides |
| Light source too close |
Where possible, min. exposure distance should be 1.5 times image area diagonal |
