M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)

Analysis - KRISTON László, JÁRÓ Márta: Impact of acid treatment of pigment samples from wall paintings on the result of paint identification by X-ray diffraction

Sample Sz-1

7 (pink) Before acid treatment it was possible to identify calcite, aragonite and a-quartz in the paint sample by the diffraction method (Photo 2a). There was no information available as to the colouring agent. As a result of the acid treatment the calcite and aragonite decomposed, the relative concentration of hematite increased and became identifiable (Photo 2b). Yellow ochre (Sample Sz-2) Concluding from the diffractogram taken of the untreated sample the paint was found to contain calcite, a-quartz and poorly crystallized goethite (Fig. 4a). The acid treatment did not bring about structural changes in the goethite, but the removal of calcite did not improve its detectability (Fig. 4b). Ca: calcite Ca G : goethite/yellow ochre/ Q : oc-quartz 55 50 45 40 35 30 25 2iy » « 1 1 1 I I I Fig. 4 Diffractogram of yellow paint sample No. Sz-2 a, before acid treatment b, after acid treatment Green earth, Egyptian blue (Sample F—

1074) Preliminary testing by X-ray fluorescence [5] showed that the paint sample consists of a mixture of pigments containing iron and copper. This was confirmed by the diffractogram taken before the acid treatment as besides calcite and a-quartz it was