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W21 – Leaflet

AMSTERDAM - Multi-purpose printability
Version: 2019-08


The scumming test is a rapid and simple method to access the tendency of offset papers to scumming. The practical conditions are approximated as much as possible in this laboratory test.
Scumming of the lithographic plate in offset printing may be caused by the printed paper. During offset printing paper is moistened by the rubber blanket. Depending on the number of times the moistening takes place (multi colour offset printing) and the resistance of the coating against water, certain compo-nents of the coating will be dissolved and deposited on the blanket, from which they are transferred to the plate. This may lead to discolouration in the non image areas of the print. This phenomena may be of dual nature: tinting and scumming. Tinting occurs when the paper components are decreasing the interfacial tension between ink and water in such a way that an ink/water emulsion is formed. The scumming is the result of a decrease in the water sensitivity of the offset plate, so that non image areas accept ink and is the more serious as it may be ruining the plate during the press run.

Method of operation

  • It is recommended to execute the test in the standard atmosphere; to most standards it is 23,0 ± 1,0 °C and 50 ± 2% rh.
  • For the operation of the AMSTERDAM, Inking Unit and ink pipette follow the instructions of manuals, IGT Information leaflet W100 and displays accurately.
  • Handle the samples carefully.



Anilox disc, 4 engravings *)

Doctor blade holder

Doctor blade flexo

Top roller with 4 segments for conventional inks

IGT ink pipette

Printing disc, rubber, 65 Shore A, 35 mm

Strips of aluminium offset plate, 50 mm

Strips of paper “T” (scumming), 22 mm

Strips of paper “O” (non-scumming), 22 mm

Stop out solution

IGT offset ink

Strips of paper to be tested (25*270 mm2)
3 strips per type of paper

Sheet of glass
about 300*400 mm2

Blotting paper
about 300*400 mm2

Plastic foil
about 300*400 mm2

Tap water or fountain solution

Lint free rags and cleaning naphtha


  1. Condition the papers, the ink and equipment during > 6 hours in the standard atmosphere.
  2. Cut the paper strips and mark them with top and/or bottom side, machine and/or cross direction and a code for the type of paper.
  3. Remove the brush from the tester.
  4. Select method Scumming.
  5. If desired, touch the checkbox Scan to scan and save the test results of the test strip
  6. Fill the ink pipette with the offset ink.
  7. Adjust the High Speed Inking Unit 4 with the following settings:
    • Water bath: 23,0 °C
    • Top roller: 4-segmented, rubber for conventional inks
    • Mode: 2
    • Startup time: 10 s
    • Distribution time: 20 s
    • Distribution speed: 0,5 m/s
    • Inking time printing discs: 15 s


  1. Prepare the contact of the strips of offset plate with the strips of paper:
    1. Remove the light sensitive layer from three strips of aluminium offset plate by rubbing them with cotton wool soaked in stop-out solution.
    2. Rinse the strips thoroughly with water and keep them drenched in water or fountain solution.
    3. Put the wet strips of plate with 15 mm distance side by side on the sheet of glass with the cleaned side up. Keep the strips flooded with water or fountain solution.
    4. Put strips of the paper to be tested, paper strips “T” (scumming) and paper strips “O” (non-scumming) with 15 mm distance across the plate strips.                                                                                            NOTE: Do not use 40 mm from the top and bottom of the plate strips in connection with possible fingerprints.
    5. Record the sequence of the paper strips.
    6. Cover the strips with a sheet of blotting paper soaked in tap water of fountain solution and pour tap water or fountain solution on the blotting paper.

NOTE: The blotting paper and the plastic foil (see point 1.7) should not cause scumming. Before using these materials in a test they have to be examined following the method described in this Information Leaflet

  1. Cover this combination (glass, strips and blotting paper) over with plastic foil (see note in point 1.6).
  2. Leave for about 3 hours.
  3. Touch the button PRINT to rotate the 1st shaft into the start position.
  4. Apply 0,19 cm3 of IGT offset ink to a segment of the inking unit and dis-tribute the ink during the preset or desired time.NOTE: It is not advised to add some ink after a test.
  5. Place the printing disc on the printing disc shaft of the inking unit and ink the disc during the preset or desired time.
  6. Take a wet plate strip from the sheet of glass and mount it on the sector by attaching the beginning of the test strip into the front clamp and if desired, fixing the end of the test strip on the sector with a piece of tape.
  7. Remove the printing disc from the inking unit and place it on the 1st printing disc shaft of the tester.
  8. Press both side buttons to make a print, if activated to move the camera downward to make a scan and to come into the end position; then release the side buttons.
  9. If the camera is activated:
  10. The test strip is assessed; if finished the camera moves upward.
  11. Save or discard the results
  12. Observe the offset plate if ink has been transferred to the location of the strip, which had contact with the paper “T”:
  13. If no ink has transferred, repeat points 7 thru 9 until ink has transferred at the location of paper “T”.
  14. If ink has transferred, continue with point 10.
  15. Remove the plate strip from the sector.
  16. Check on which parts of the strip ink has been deposited as pointed out in the chapter “Assessment”.
  17. Remove the printing disc from the tester and clean it with the rags and naphtha.
  18. For a next test start with point 3 or touch BACK and start with point 2. It is recommended to perform the test at least three times per sample.
  19. After having finished the tests, touch BACK and clean and store all parts as described in the manuals.
  20. Make an accurate record of the conditions and the results of the test and refer to W21-AMS.


  1. Examine the plate strip visually which parts have accepted ink (see figure 2):
    • Paper “T”: the plate accepted ink.
    • Paper “O”: the plate did not accept ink
    • Paper to be tested:
      The plate accepted ink, so the paper is causing scumming
      The plate did not accept ink, so the paper does not cause scumming.
  2. Repeat point 1 for each test strip.


Randstad 22 - 02

1316 BX Almere

The Netherlands

P.O.box 22022

1302 CA Almere

The Netherlands

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