The Difference Between Doubling and Slurring in Offset Printing

The difference between doubling and slurring in offset printing is the the cause.  The result looks almost exactly the same.  Here is what both slurring and doubling generally look like.

Slurring and doubling are an elongation of a printed dot.  The difference lies in the cause.  For example, slur happens in the direction of the paper travel while it goes through the press.  Doubling can happen in any direction. Here is a list of what can cause slur or doubling:

• blankets packed improperly
• loose blanket(s)
• bad cylinder bearings
• poorly timed grippers (sheetfed)
• worn gripper pads (sheetfed)
• poor infeed setup
• lateral movement (web)
• bad side guides (sheetfed)
• smashed blanket or cylinder surface
• drive gears misaligned
• registration adjustment
• distortions in paper
• blankets not torqued properly

Correcting any one of those issues are another article all unto themselves. Let's cover a few of them:

Doubling caused by distortions in paper

In sheet fed printing, doubling can occur as a result of prekissing.  This is when the paper prematurely contacts the offset press blanket and causes an image double. It is literally a double print of the image, and not a slur. This defect can be caused by paper distortions such as waviness or static electricity.

On web presses a paper defect causing waviness on one part of the web will cause a doubling effect.  This lack of tension in one part of the web can only be controlled by increasing tension until the wave is gone. If it can't be controlled, the paper must be rejected as a paper defect.

Slurring caused by registration adjustment

In color printing, any movement of the plate cylinder will cause it to slide against the blanket.  This is an expected result and cannot be avoided, only minimized.  In order to minimize it the press operator can make the move very slowly in or in minute adjustments.  If the adjustment is made automatically, the adjustment can be programmed to be moved very slowly. 

Slurring caused by blankets being poorly packed

Improperly packed blankets will cause the diameter, and hence surface speed of the plate and blanket cylinder to run at different speeds.  In order to compensate a slip will occur between the two.  This is slurring.

Doubling or slurring from blankets being loose

This is the first thing that should be checked when experiencing this problem.  In fact doubling and slurring can both occur as the problem can happen in any direction.  Especially if the blankets are not mounted properly.  The press operator should know the proper torque for the blanket to be mounted and check them regularly. 

Please leave a comment below if I have missed any possible explanations.