If the ink stain is in a book, place a paper towel behind the page so that the solution doesn't soak through. Mix one part muriatic acid with five or six parts water. Apply to the ink stain and leave on for two minutes before wiping off and drying. This process should be repeated as often as needed to remove the stain and is considered the "go-to" method for most ink stains on paper.
Using citric and vegetable acid is safer than muriatic acid and doesn't require careful mixing or much diluting, yet is slightly less effective. Mix a solution of citric acid, Oxalic and Tartareous acids diluted in water. Such a solution is safe to use on paper and precious fabrics. This solution can remove ink stains, but not printing ink; therefore it is safe to use on extraneous ink marks in books without eradicating the printed works.
Use a 91 percent isopropyl alcohol solution and nail polish remover, which contains acetone. Certain types of ink will be easier to remove than others using either the former, the latter or a concoction of both. Gel pens, for instance, are fairly immune to both methods. Other cheaper ink pens, on the other hand, tend to be effectively removed by these methods.
Printed ink, whether it be laser or deskjet ink, is difficult to remove with solvents as the process of ink printing melts the ink into the fibers of the paper. If the printed ink has stayed on the page for a long period, it may even be impossible. In an attempt to remove printed ink, make sure it is freshly printed. Blot the erroneous ink with small amounts of water and then scrape the ink off with a small razor in one direction.