Conference Agenda

Saponification occurring in paint layers represents a serious degradation process affecting the appearance and stability of paintings, leading for example to protrusions, efflorescence, darkening, delamination, exudates etc. A substantial part of saponification is formation of metal carboxylates, resulting from the interaction between metal cations (e.g., Pb²⁺, Zn²⁺) released from pigment particles (e.g., lead white, red lead, zinc white) with fatty acids (usually palmitic and/or stearic) released from triglycerides making-up oil-based binders. Metal carboxylates can adopt variable structures from ionomers to amorphous complexes to crystalline phases, and up to now the mechanism of their crystallization is not elucidated. Moreover, crystal structures of most metal carboxylates are not determined. This paucity complicates the study of the degradation process and clarifying of factors promoting or inhibiting the saponification. However, without knowledge of degradation mechanism it is impossible to find a suitable strategy to prevent it.

Within the study of miniature paintings by combination of non-destructive spectroscopic and diffraction techniques (X-ray fluorescence, infrared spectroscopy and X-ray powder diffraction), unusual patterns of crystalline metal carboxylates together with the red pigment cinnabar (HgS) were detected Fig.1 [1], indicating the possible effect of the cinnabar on the formation of these carboxylates.

Figure 1. Part of diffraction patterns of the miniature portrait J2037 with the best evidence of all important lines of metal soaps in low angle region (S lead soaps, H hydrocerussite, K kaolinite, HgS cinnabar, G gypsum, M mica, A anhydrite)

The necessity to identify metal soaps found in the paintings and to understand their formation, the synthesis of mixed mercury carboxylates was carried out. The composition of the mercury carboxylates corresponds to the formula Hg(C16)_x(C18)_2-x (where C16 is a palmitic acid and C18 is a stearic acid, x from 0 to 2,0 with 0,1 increments). The synthesized compounds serve as reference materials for the study of the degradation processes performed on model the paint layers. The synthesized carboxylates of the formula were investigated by X-Ray powder diffraction (XPRD), Fourier-transform infrared spectroscopy (FTIR) and ultra-wideline solid state nuclear magnetic resonance spectroscopy (ssNMR).

The structural model of selected prepared mercury carboxylates was described from the refinement of the obtained XRPD data complemented by DFT calculations from obtained ssNMR spectra. Previously reported data for lead palmitate-stearate was used as a reference. [2] We revealed that both hexadecanoate (C16) and octadecanoate (C18) chains are present in one crystal structure, creating the statistical disorder at the ethyl end of the chains.

[1] Garrappa, S., Hradil, D., Hradilová, J. et al. Non-invasive identification of lead soaps in painted miniatures. Anal Bioanal Chem 413, 263–278 (2021). https://doi.org/10.1007/s00216-020-02998-7

[2] Kočí E, Rohlíček J, Kobera L. et al. Mixed lead carboxylates relevant to soap formation in oil and tempera paintings: the study of the crystal structure by complementary XRPD and ssNMR. Dalt Trans. 2019; 48:12531–40. https://doi.org/10.1039/C9DT02040C

The contribution aims at explanation of the meaning of Jamnitzer´s work [see also 1], especially elucidation of the relationship between the perspective, i.e. the method how the visual perception of the world can be mathematized, and five regular (Platonic) solids. Four elements, i.e. Fire, Air, Earth and Water, have been traditionally attributed to the tetrahedron, octahedron, cube and icosahedron, respectively (Plato´s Timaios). The dodecahedron symbolized the Fifth essence or Universe or God´s substance by Jamnitzer’s own words.

Jamnitzer intended to treat natural phenomena by combinations of the elements following Plato´s Timaios. It is manifested by depiction of the regular bodies and their transformations about their common symmetry elements in aesthetically appealing engravings. However, in agreement with the Christian creed, this view about the world goes beyond its visible part. Jamnitzer’s work can be interpreted that invisible world can be understood at least at part by adopting geometry and arithmetic which is a way how a human being can get closer to the Creator.

Wenzel Jamnitzer´s work was one of the treatises of this kind which were published between 15-17^-th centuries [2]. This means that his work can be considered as a representative of the culture which was flourishing at that time. Among his predecessors were such important personalities like Luca Pacioli/Leonardo da Vinci (the manuscript De divina proportione, 1498-1499) and Albrecht Dürer, author of Underweysung der Messung, mit dem Zirckel und richtscheyt, in Linien, Ebnen und gantzen Corporen, Nürnberg (1525) who was also a Nürnberger citizen and a goldsmith at the very beginning of his career likewise Jamnitzer. Jamnitzer’s work shares similarities with Leonardo’s illustrations to Luca Pacioli’s treatise. It should be emphasized that Nürnberg was a centre of crafts as well as of German/transalpine humanism [1], [3] and it seems not to be coincidence that it was just there where Copernicus´s book De revolutionibus orbium coelestium libri VI was printed in 1543 by a famous printer Johannes Petreius.

The ideas which are manifested in the discussed Jamnitzer´s work have been reflected in Johannes Kepler´s books, i. a. in Mysterium cosmographicum or in Strena seu de nive sexangula (Francfurt a. M., 1611), the treatise so important for crystallography. Other examples of the applications of these ideas in architecture - see e.g. [4], [5] - and in arts - e.g. [6] will be shown. Importance of measurement as a method how to approach to the surrounding world will be emphasized in the contribution.

The author thanks the Institute of Physics for the support.

[1] Albert FLOCON (1993). Preface to translation into Spanish by Elena del Amo: Wentzel JAMNITZER, Perspectiva corporum regularium, Nürnberg 1568. Spain: Edición Siruela.

[2] Kirsti ANDERSEN (2007). The Geometry of an Art : The History of the Mathematical Theory of Perspective from Alberti to Monge, p. 212 and p. 224, New York: Springer.

[3] Martin KEMP (1990). The Science of Art. Optical themes in western art from Brunelleschi to Seraut, p. 63. New Haven and London: Yale University Press.

[4] John G. Hatch, The Science Behind Francesco Borromini's Divine Geometry, pp. 127-139 in Nexus IV: Architecture and Mathematics, eds. Kim Williams and Jose Francisco Rodrigues, Fucecchio: Florence: Kim Williams Books, 2002.

[5] George L. Hersey (2000). Architecture and Geometry in the Age of the Baroque. The University of Chicago Press: Chicago.

[6] Miguel Falomir, Lynn Roberts, Paul Mitchell (2017). Arcimboldo. Las Floras y la Primavera. Museo de Bellas Artes: Bilbao.