Canon PIXMA iP2850 - Manual (Page 185)

Back of the Paper Is Smudged
Check1 Did you confirm the paper and print quality settings?
Print Results Not Satisfactory
Check2 Perform the Bottom Plate Cleaning to clean the inside of the printer.
Cleaning Inside the Printer
Note
• When performing duplex printing or too much printing, the inside may become stained with ink.
185