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

Red ochre, cinnabar, minium (?) (Sample F-256) Based on prior examination by X-ray fluorescence [5] the paint consists of a mixture of pigments containing iron, mercury and lead (Fig. 2). • H

9 Hg sjo 150 150 channel number •» Fig. 2 X-ray fluorescence spectrum of the surface of red mural fragment No. F-256 Concluding from the diffractogram taken of the sample before the acid treatment - besides calcite and a-quartz - only mercuric sulphide may be identified with certainty, the presence of hematite being dubious (its concentration is near the detection limit), while no compound containing lead may be observed (Fig. 3a). Treatment by hydrochloric acid brought about structural changes neither for mercuric sulphide nor for hematite (Fig. 3b). The latter became safely identifiable since as a result of removing calcite, the proportion of pigments increased and consequently their reflections increased. Inferring from the new reflections on the diffractogram, lead-chloride seems to have developed - most probably through the transformation of lead(II,III)-oxide (minium). The characteristic "d" values of lead-chloride are shown in Table 4. Table 4 Characteristic "d" values for lead chloride Compound No. of ASTM card Characteristic d values (nm) (relative intensity given in the index) Lead-chloride 5-416 0358

10 0.289

7 0.278

5 0.251

4 O.38I4 O.2IO3 O.4O63 0.215

3