Here is a list of problems that need to be paid attention to during the process of offset printing Uneven colour: Always make sure that the colour is the same on both sides of the sheet by rolling the sheet up so that you can look at opposite edges of the sheet side by side.
Ghosts: These are either

• images formed in areas where they should not appear, or
• formation of lighter areas where there should be even inking.
  

Hickies (aka Fish-Eyes): These are non-inked circles created by lint on the plate or blanket.
They are generally something that can be cleaned up when appearing on several sheets in a row.
However, chances are you will never be able to eliminate every single hickie, especially if you have large solids in your printing piece and have to print thousands of sheets.
Picking: These are the non-inked areas that look like snow created in areas where the ink and some of the paper has been lifted off the sheet when the ink is too tacky.
Note : Picking can occur due to a paper related problem.
Muddy or Uneven Screens : These occur as a result of dot gain (see SCREENS.
) In the worst case scenario caused by a muddy or uneven screen, you may need to remake a plate using a coarser screen.
However, some dot gain can be alleviated by

• running the ink a little lighter and
• by ensuring that the gradients on your piece, if any, look even.
  (Refer to GRADIENTS to see how to avoid banding in the design and prepress stages of the job.
  )

Offsetting: This is the appearance created on the back of a sheet by an image present on the sheet touching it.
Offsetting happens as a result of

• too much ink
• insufficient driers in the ink or
• trimming of the job done when the ink is too wet