Production and characterization of lead, tin and antimony based yellow pigments

Claudia Pelosi, Ulderico Santamaria, Giorgia Agresti, Elisabetta Mattei, Alberto De Santis.

Keywords artificial yellow pigments, colorimetry, XRD, SEM-EDS, micro-Raman

This study deals with the preparation of artificial yellow pigments which have confusing terminology in the historical references (Seccaroni 2006). By analyzing the various recipes concerning lead-tin-antimony yellows, it was possible to reconstruct the original production methods of these pigments, though the experimental conditions are not clear (temperatures are not indicated, time is often unspecified and materials are not clearly reported). We produced lead-tin yellow ‘type I’ (Pb2SnO4) and lead-tin yellow ‘type II’ (PbSnO3 or PbSn1-x SixO3) following the indication of the recipes 272 and 273 of the fifteenth century Bolognese Manuscript, lead antimonate yellow (Pb2Sb2O7), called Naples yellow, according to the treatises written by Piccolpasso, Passeri and Valerio Mariani from Pesaro, and lead-tin-antimony yellow (Pb2SnSbO6,5) from the Darduin, Valerio Mariani da Pesaro and other authors. More recent work, dealing with the production and analysis of artificial yellow pigments, were taken into account (Cascales et al. 1986; Clark et al.1995; Kuhn 1993; Moretti et al. 1984).

The study of lead, tin and antimony based yellow pigments, produced in a laboratory using ancient procedures, is also useful for investigations on similar materials used in works of art (Pelosi et al. 2007). Indeed, it is very probable that the artists chose their painting materials by selecting not only the colour of the pigments but also the production method. Therefore, it is important to state a correlation between chemical compositions, ancient production methods, and the final colour of the produced yellow pigments.

The production of lead-tin-antimony based yellow pigments was obtained by pure chemical oxides (PbO, Pb3O4, SnO2, Sb2O3 and SiO2), supplied by Across. Sodium chloride, used in the production of lead antimoniate according to the recipe of Valerio Mariani from Pesaro, was supplied by ICN. The oxides were mixed in agate mortars and then introduced into the furnace at room temperature. They were warmed up to the required temperature. The temperature was maintained constant for 5 hours. Only for the production of lead-tin yellow type I a time of 3 h was also tested. Then the samples were allowed to cool slowly inside the furnace. In order to evaluate the influence of cooling condition, lead-tin-antimony yellow was also cooled in cold water at 10 °C. The temperature was different according to the typology of pigment to be produced (670, 800 and 900 °C for lead-tin yellow type I and type II; 900, 950 and 1050 °C for lead antimonate; 925 °C for lead-tin-antimony yellow). For the production of lead-tin yellows porcelain crucibles were used; for lead antimonate and lead-tin-antimony yellow porcelain crucibles and terracotta tiles covered by filter paper were used. The obtained products were characterized by SEM-EDX, XRD and micro-Raman analyses. Colour measurements were performed on the ground samples with an X-Rite spectrophotometer according to CIE 1931 and CIE 1976 specifications, employing light sources C and D65 and a 10° observer. Colour parameters were mathematically treated to obtain the dominant wavelength (λd) and the colour purity (P%).

Lead-tin yellow type I was produced at a temperature of 800 °C for 5 hours. At a lower temperature the compound Pb2SnO4 was not completely formed. The correct stoichiometric ratio was Pb:Sn = 2:1; the volume ratio was incorrect. Using Pb3O4 or PbO does not change the final product. Lead-tin yellow type II was produced at a temperature of 800 °C or higher using the compound Pb2SnO4 and SiO2 (10% w/w). At lower temperatures a mixture of Pb2SnO4 and PbSnO3 was formed.

Lead antimonate, or Naples yellow, was obtained with two different recipes: the first one using only the pure chemical oxides (Pb3O4 and Sb2O3); the second adding NaCl to PbO and Sb2O3, according to Valerio Mariani from Pesaro. In both cases a mixture of compound was obtained. The best pigment was produced at 900 °C for 5 hours with a stoichiometric ratio Pb:Sb=1:1 over terracotta tile. In this sample the compound Pb2Sb2O7 was identified by XRD, SEM-EDX and micro-Raman analyses. The addition of NaCl probably led to the production of oxychlorides which were not well characterized.

Finally, lead-tin-antimony yellow was produced at 925 °C for 5 hours. The obtained compound corresponds to the formula Pb2SnSbO6,5 (JCPDS 39-0928). Experimental tests showed that a mixture of compound was often produced and that temperature played an important role in the composition and colour (hue and purity) of the produced pigments. The stoichiometric ratio of the metallic elements in the chemical oxides was also an important parameter. In fact the use of a volume ratio led to the production of the expected pigments, but some reagents remained in the final product. For the production of lead antimonate further experimental tests must be carried out in order to understand the role of temperature, type of crucible and ingredients. In this preliminary phase of the research we chose to make a simplification of the recipes, in particular to eliminate some ingredients whose role was not completely clear. Further experimental tests will be tried out to obtain a better understanding of the role of these ingredients (zinc oxide, lees of wine i.e. potassium hydrogen tartrate and NaCl) indicated in the recipes.

References

Cascales, C., Alonso, J.A. andRasines, I. 1986. ‘The new pyrochlores Pb2(MSb)O6,5 (M=Ti, Zr, Sn, Hf)’, Journal of Materials Science Letters, 5:675-677.

Clark, R.J.H., Cridland, L., Kariuki, B.M, Harris and K.D.M., Withnall, R. 1995. ‘Synthesis, structural characterisation and raman spectroscopy of the inorganic pigments lead tin yellow types I and II and lead antimonate yellow: their identification on medieval paintings and manuscripts’, Journal of the Chemical Society-Dalton Transactions, 16:2577-2582.

Kuhn, H. 1993. ‘Lead-Tin yellow’. In A. Roy (ed.), Artists’s Pigments, vol. 2, (ed.), Washington: National Gallery of Art, 83-112.

Moretti, C. and Hrelich, S. 1984. ‘Opacizzazione e colorazione del vetro mediante le anime’, Rivista della Stazione Sperimentale del Vetro, 1:17-22 e 2:83-87.

Pelosi, C., Santamaria, U., Morresi, F., Agresti, G., De Santis, A. and Mattei, E. 2007. ‘I gialli di piombo, stagno, antimonio: le opere di Poussin e Saraceni’, in Claudio D’Amico (Ed.), Atti del IV Congresso Nazionale di Archeometria, Padova: Pàtron Editore, 81-94.

Seccaroni, C. 2006. Giallorino. Storia dei pigmenti gialli di natura sintetica. Roma: De Luca Editore.

Authors’ addresses

Claudia Pelosi, Facoltà di Conservazione dei Beni Culturali, Largo dell’Università, 01100 Viterbo, Italy. ()

Ulderico Santamaria, Facoltà di Conservazione dei Beni Culturali, Largo dell’Università, 01100 Viterbo, Italy, and Laboratorio Scientifico dei Musei Vaticani.

Giorgia Agresti, Facoltà di Conservazione dei Beni Culturali, Largo dell’Università, 01100 Viterbo, Italy.

Elisabetta Mattei, Facoltà di Agraria, Via S. Camillo De Lellis , 01100 Viterbo, Italy.

Alberto De Santis, Facoltà di Agraria, Via S. Camillo De Lellis , 01100 Viterbo, Italy.

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