Aqueous treatments of paper objects showing signs of ink corrosion are still controversially discussed in the paper conservation field. Such treatments offer considerable benefits, but are often accompanied by unwanted side effects especially in the case of ink corrosion. Side effects can appear directly after the treatment (immediate side effects), but can also occur after a certain period of time (long term side effects). Side effects include cracking of ink lines during immersion, colour changes of inks and papers, formation of crystals on the ink surface, and migration of soluble components (bleeding). In order to avoid such side effects it is necessary to understand their causes. For instance the pH of aqueous solutions, the presence and concentration of dissolved salts, the application method used and other parameters definitely influence the result of the washing procedure. The appropriate application of a given conservation treatment is therefore required in order to avoid unwanted changes of the object due to treatment.