Scumming – Causes and Solutions

When it comes to offset print scumming, I will assume you know enough about ink and water balance to know how to make it go away.  I would like to go into some of the deeper reasons as to why scumming can happen and what remedies can solve this plague.  First of all, let’s define scumming.


In offset printing, when the non-image areas of a plate become receptive to ink, that’s scumming.  Too much ink or not enough water is not a definition.  Those are causes.  Since the causes are so many, that definition is broad enough to encompass most reasons. 

Causes of Scumming

Let’s now look at a few causes of scumming beyond the simple ink and water balance solution.

  • Plate is sensitized by piling.
  • Dirty metering or water pan roller.
  • Poor plate development.
  • Poor ink strength.
  • Bad roller settings.

The Right Tools

You need the right tools to combat this issue. Scumming usually starts invisible to the naked eye. Be sure you have the proper tools to identify it.  We use this product which is cheap and sold on Amazon.  There are other higher end ones like this one, but the point is this, don't just use your naked eye.

Scumming Solutions

There are several different areas that we can look at from this point.  Let’s examine each consumable one at a time. 

1.  The press itself.  Start here.  Check all the roller settings and get them set them exactly to the press manufacturers specs.  Take your time and check the settings when the roller are engaged.  There is a difference.

2.  The plate.  We have found that sometimes our plates are too sensitive.  It turned out once that gum wasn’t properly being applied by our plate room department.  Whatever the case, a very narrow window can be created if plates are not processed properly.  If the press is down for any significant time, gum your plates.  We have found that plates made by computer-to-plate can oxidize fast and must be gummed quickly.

3.  Chemistry.  Start with your fountain solution.  Double check that you are mixing it according to the manufacturers specifications.  Consult with your supplier that your paper is made compatible with your paper and plate.  Poor chemistry can cause piling which leads to the next area.

4.  Piling.  The buildup of piling can be abrasive enough to the plate that is will cause it to desensitize and scum.  There are so many causes of piling that are difficult to troubleshoot that we cannot discuss them all here, but in our experience, paper is the place to start.  Paper that is too abrasive will desensitize the plate quickly.  A higher grade of paper may help.

 5.  Ink.  In our experience ink is responsible for 3% of the cost but 97% of the quality.  Good offset printing ink is worth its weight in gold.  A liberal ink and water balance window is critical to prevent scumming.  Work closely with your ink supplier and discuss values like ink and water pickup rate.  Ink manufacturers take shortcuts too.  Call them on it!

I do not necessarily go in this order.  My first suspect is always setting and then ink, but you make the call and let your experience be your guide.


  1. Anonymous9:06 AM

    You have left out one important cause of scumming.
    Improperly over packed cylinders. To much squeeze between plate and blanket will give you scumming problems like you would not believe. We know first hand the problems it can cause. Give yourself a max squeeze of .006 between plate and blanket and you can rule out this issue.

  2. Anonymous10:59 AM

    Does the combination of too much water and too much ink result in press scum?

    1. Anonymous1:32 PM

      Yes! Always start by backing off the ink when your scumming, but please always check your water ph first. If the water is okay, and ink correct density, roller settings and hardness are the next steps

  3. Anonymous9:26 AM

    Another important cause is imbalance in fountain solution mixture.

  4. Anonymous12:41 AM

    how is the alchole effect to scumming?

  5. Alcohol has good property of charge it can travel freely in non image area which eliminates scumming but we should rather check all settings first.

    1. Anonymous11:37 PM

      what happen if we use high alcohol ration

  6. Anonymous6:19 AM

    if we do normal printing after uv printing and got scumming problem then what remedies should we take after applied all these settings writtened above.
    this is the common problem we r facing when we do normal printing after uv printing and vice versa

  7. What can be done in order to thicken ink in very hot weather?

    1. The only think that can be done is to get your ink supplier to give you ink that works in such weather. It is a formula issue and there's nothing you can do to "thicken it" in the pressroom. The only think you can do is have air blowing on the ink rollers that is dry air - perhaps from your compressor - and this will help to maintain balance.

    2. Thank you Bill and good morning too all. I will try the fan fan and hopefully it should solve some problems.

    3. Anonymous1:33 PM

      We used to put ink outside in freezing weather, just to make it easy to handle by hand, it had no effect on printing

  8. What causes water washing in between the printed material,when ink and dampening settings are perfect?

  9. Anonymous11:31 PM

    I have a peculiar problem that I am facing, I use Fuji Positive Thermal CTP plates on my Luscher Expose CTP, what I am getting is slight scum on plate edges, which is causing scum while printing and because I am printing Edge to Edge on the paper, this is causing problem. I am informed by the CTP engineer that the Burr on plate edge is causing it but the plate manufacturer says the burr is mimimal and within tolerance and that it shouldnot cause the problem.Can anybody help me out with some suggestions on this matter on how to avoid the scum on press on the edges of print.

  10. Put some plate desensitizer on it. Eg. Scratch remover solution.

  11. what is the correct pressure to be set on a MOVP 1992 press for 20lb / 75gsm bond paper. I am getting scumming on the sheets. I am a first time pressman and learning my press. Help needed please.

  12. Anonymous8:14 AM

    I have scumming problem in metallic ink p.871 . After 10.000 presses i have to make new plate because old one damaged even if cleaning every 1000 presses

    1. This is normal for metallic ink. I've had the same problem. I always had several plates made in advace for this issue. The only thing that helped was putting a little reducer in the ink to thin it out a little bit.

  13. Anonymous9:54 AM

    The plate is picking background when printing. What is it? How can we achieve a good print?


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