The report, in two parts, describes the problems involved in the restoration of the 1623, 5th edition of a Mercator Atlas. The paper was extremely discolored and acidic in nature. The colored maps contained areas originally painted green which, now turning a deep chocolate brown in color, have caused embrittlement of the paper, even its disintegration and loss. As the pigments of the maps are at least partially water-soluble, non-aqueous methods of restoration seem indicated. An investigation into the paper is described using, among other techniques, SEM combined with x-ray microanalysis. The presence of CaCO₃, CaSO₄, Fe₂O₃ K₂SO₄, Al₂ (SO₄)₃ was determined and the crystals photographed. The implications of these findings in relation to the generally-accepted historical develop-ment of the use of alum in paper sizing is discussed together with the more serious implications of the presence of Fe₂O₃. The advantages/disadvantages of attempting to remove iron compounds from old papers are summarized. The second part of the report discusses paper deacidifica-tion -- what causes acidity, how it can be removed/neutralized and the latest research findings which underline the paramount importance of using calcium compounds for deacidification. A new non-aqueous method, involving the use of calcium acetate dissolved in ethanol is proposed and justified. Authors' addresses: Carlo Federici, Istituto di Patologia del Libro, Via Milano 76, 00184 Roma, Italy; Margaret Hey, Conservation Department, Trinity College Library, The University, College Street, Dublin 2, Eire.