The chemical process of treating a lithographic plate or stone with a weak acid and gum arabic solution to ensure the non-image areas remain hydrophilic and oleophobic. This treatment prevents ink from adhering to the blank spaces during the press run. If a plate is improperly treated, ink will gradually build up in the background areas and cause scumming on the printed sheets.
Heard on the job
Make sure you desensitize the plate thoroughly or we'll get scumming across the whole background after a hundred impressions.
Insider tip
A poorly desensitized plate is the most common cause of background tinting or scumming on long web runs.