The contact with the paper media having varying acidities induces phenomena of oxidation or else a chemical reaction between the parts in contact with each other. The example reports the markings of a seismogram (b) in two sheets of paper of the handwritten notes (a, c) in between which the seismogram is placed. The different acidity of the seismogram as compared with the other two sheets has caused these markings. In order to reduce these effects it is necessary to interpolate chemically neutral paper (pH = 7).