Mass deacidification treatments are used as a preventive measure against deterioration of paper-based cultural property. There are many criteria for the selection of a good mass deacidification method, for example, pH or alkaline reserve level, toxicity, odour, cost and so on. One of the criteria discussed in this paper is the homogeneity of mass deacidification treatments in current use. Since the acidification of books does not occur in a homogeneous manner, can homogeneity be considered a good criterion? What are the differences, from this point of view, between a vapour phase method (diethyl zinc) and liquid methods such as methoxy ethoxy methyl magnesium carbonate or the FMC process? The authors show the results of measurements by flame atomic absorption spectrometry (AAS) of the concentration levels of magnesium or zinc found in different locations on sheets of paper treated by these three methods.