Scumming
Dealing with scumming
Unigraph offers you a short and practical guide in helping circumvent one of the most common printing problems: scumming (greasing). Scumming occurs when non-image areas of the plate begin to accept ink. Do not confuse scumming with tinting, which is generally characterized by a light uniform ink film over the entire plate. There also exists simple procedures to distinguish between both problems. Increase the flow of fountain solution or hone the plate with a desensitizing stick while the press is stopped. At restart, if the problem diminishes or disappears, it’s most likely scumming. If your diagnosis leans toward scumming, we suggest a series of probable causes and associated remedies.
1. Scumming may arise due to inadequate dosage of fountain concentrate, alcohol or alcohol substitute:
2. Scumming may be ink related:
3. Scumming may appear if insufficient dampening solution is transferred to the plate:
4. Too quick evaporation of the thin water film on the plate may cause scumming:
5. Scumming may also come from a faulty plate:
Going through this troubleshooting procedure may help you to identify the problem and the cause, thus leading to the appropriate action to take. Keep in mind that tinting, bleeding and plugging may leave an image similar to scumming, however, the causes could be essentially different.
Unigraph offers you a short and practical guide in helping circumvent one of the most common printing problems: scumming (greasing). Scumming occurs when non-image areas of the plate begin to accept ink. Do not confuse scumming with tinting, which is generally characterized by a light uniform ink film over the entire plate. There also exists simple procedures to distinguish between both problems. Increase the flow of fountain solution or hone the plate with a desensitizing stick while the press is stopped. At restart, if the problem diminishes or disappears, it’s most likely scumming. If your diagnosis leans toward scumming, we suggest a series of probable causes and associated remedies.
1. Scumming may arise due to inadequate dosage of fountain concentrate, alcohol or alcohol substitute:
| Cause | Remedy |
| • Not enough concentrate. | • Check dosage, keep at recommended pH and conductivity. |
| • Too much concentrate. | • Check dosage, keep at recommended pH and conductivity. |
| • Low alcohol or alcohol substitute. | • Contact your fountain solution manufacturer. |
2. Scumming may be ink related:
| Cause | Remedy |
| • Too much ink being carried and squashed over non-image areas. | • Reduce ink feed or use a denser ink pigment. |
| • Ink is too soft and spreads over non-image areas. | • Add heavy bonded varnish to ink. |
3. Scumming may appear if insufficient dampening solution is transferred to the plate:
| Cause | Remedy |
| • Too little fountain solution. | • Increase flow of fountain solution. |
| • High dampening temperature (low viscosity). | • Ideally, should range between 10-15º C (50-60º F). |
| • Dirty, worn dampener sleeve or metering roller. | • Clean or change devices. |
| • Improper dampening settings. | • Reset dampeners to appropriate settings. |
| • Improper form roller settings. | • Check and adjust stripe on plate. |
| • Improper roller durometer. | • Measure and change to specifications. |
| • Improper plate/blanket packing. | • Set according to instruction manual. |
| • Glazed blanket. | • Clean all gum, ink and particulates. |
4. Too quick evaporation of the thin water film on the plate may cause scumming:
| Cause | Remedy |
| • High dampening temperature. | • Ideally, should range between 10-15º C (50-60º F). |
| • Air drafts blowing on the plate. | • Prevent or shield from air drafts. |
5. Scumming may also come from a faulty plate:
| Cause | Remedy |
| • Improper gumming. | • Clean plate with water and/or cleaner conditioner. |
| • Plate not opening or not desensitized. | • Gum plate on press. |
| • Sensitive or light-struck plate. | • Desensitize plate, apply scratch remover or plate cleaner. |
| • Prepress problems: exposure or development. | • Make new plate. |
Going through this troubleshooting procedure may help you to identify the problem and the cause, thus leading to the appropriate action to take. Keep in mind that tinting, bleeding and plugging may leave an image similar to scumming, however, the causes could be essentially different.
