In the process of preservation of paper artifacts, such as watercolour, gouache or pastel, the usage of water and other solvents is generally avoided. This represents a significant obstacle, which specifically relates to the elimination of acidic paper substrate. The article presents the outcome of our research on the use of Bookkeeper’s deacidification method to preserve this type of objects. Perfluoroheptane organic liquid, which is neutral to inks, dyes and other substances that are sensitive to water and other solvents, is used as a carrier in the deacidification substance – magnesium oxide. It does not cause physical changes in the paper, typical for water treatment – cut and deformed sheets. The article shows the results obtained during the deacidification of eight watercolours and three pastels. The tests, which were continued as the basis previous studies, during which the impact of this method of deacidification on the colour stability of a model watercolour painting was examined, were prepared for two types of securities. The researches came to the conclusion expressed in the article that Bookkeeper deacidification method carried out on the verso is completely safe for the objects and does not cause significant changes in the layer of paint colours.