This study investigated samples of paper and parchment from the 13th to 16th centuries, which contained different kinds of metallogallic inks. The purpose was to establish the relationship between the degree of the darkness of the ink and its acidity, and also to evaluate the quantity of components in the reaction which produces metallogallic ink. Scanning electron microscopy (SEM) and energy dispersive x-ray microanalysis were used to check ink penetration and components' distribution in the support material. Under identical analytical conditions, the presence of sulfur and iron was identified and its concentration was compared using x-ray spectra corresponding to the two elements; however, absolute measurement was not carried out.