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An ink eraser is an instrument used to remove ink from a writing surface, more difficult than removing pencil markings. Older types are a metal scraper, which literally scrapes the ink off the surface, and an eraser similar to a rubber pencil eraser, but with additional abrasives, such as sand, incorporated. Fibreglass erasers also work by abrasion. These erasers physically remove the ink from the paper. There is some unavoidable damage with most types of paper and ink, where the paper absorbs some ink.
The chemical ink eradicator contains a substance that reacts with some inks removing their pigmentation and hiding the writing.
Metal ink erasers
Metal ink erasers were generally used before chemical ink erasers were introduced, and when permanent writing was done in ink. The erasers were essentially small knives.
Chemical ink erasers
Chemical ink erasers break down royal blue ink by disrupting the geometry of the dye molecules in ink so that light is no longer filtered. The molecules are disrupted by sulfite or hydroxide ions binding to the central carbon atoms of the dye. The ink is not destroyed by the erasing process, but is made invisible. It can be transformed back into a visible work with aldehydes.
The eradicator works only with royal blue ink. It discolors black ink to a rust brown and changes the hue of non-standard blues, limiting its usefulness.