Its Surreal: Zinc-Oxide Degradation and Misperceptions in Salvador Dalí’s Couple with Clouds in Their Heads, 1936

Abstract

The painting Couple with Clouds in their Heads by Salvador Dalí (1936) from the Museum Boijmans van Beuningen in Rotterdam was seriously disfigured by ring formations on the edges of the painting and a matt, white-looking semi-transparent material on the surface. Paint samples, taken from affected and unaffected paint areas, investigated with light, scanning electron and ATR-FTIR microscopy and X-ray diffraction showed that the zinc white-containing oil paint was converted into zinc soaps, zinc formate dihydrate, zinc acetate dihydrate and zinc sulfide. The conversion of the zinc white started at the surface of the painting. Zinc soaps are formed by a reaction of zinc white and fatty acids from the oil. Formate and acetate, most likely emitted from the wooden frame, reacted with the zinc white pigment. Finally, the zinc sulfide is suggested to derive from zinc white reacting with hydrogen sulfide.

The high degree of degradation of the zinc white-containing paint and the ring formation is postulated to be triggered by the exposures of the panels to high temperatures which occurred during a 1-day photo shoot in 1936 shortly after completion of the paintings by Dali. Furthermore, it seems likely that the glazed frame created a (semi-)closed system and subsequently acid gasses diffused into the system via “leakages” due to a poor match between the frame and the panel, and may have initiated a reaction with the surface of the painting. As the glazed and framed panels were a non-ventilated system, the acid gasses did not distribute evenly over the surface, but rather were most intense at the edges of the painting. The ring formation caused by the gasses is compared with the phenomena of Liesegang rings, a reaction-diffusion process.

Appendix

Light Microscope

Paint cross-sections were examined under a Zeiss Axioplan 2 microscope both with incident polarised light and incident UV-light (from a Xenon-lamp and a mercury short arc photo optic lamp HBO, respectively). The filter set ‘UV H365’ used for examination in UV-light consists of the following filters: excitation BP 365/12, beam splitter FT 395 and emission LP 397.

Attenuated Total Reflection – Fourier Transform Infrared (ATR-FTIR) Imaging Microscope

The FTIR spectral data from paint cross-sections were collected on a Perkin Elmer Spectrum 100 FTIR spectrometer combined with a Spectrum Spotlight 400 FTIR microscope equipped with a 16 × 1 pixel linear Mercury Cadmium Telluride (MCT) array detector. A Perkin Elmer ATR imaging accessory consisting of a germanium crystal was used for ATR imaging.

Scanning Electron Microscopy – Energy Dispersive X-Ray Spectroscopy (SEM-EDX)

A sample from the male figure was analysed using a JEOL JSM 5910 LV SEM and Noran Vantage EDX system with Pioneer Norvar detector. Analysis of samples taken from the female figure were performed using a XL30 SFEG electron microscope (FEI, Eindhoven, The Netherlands) with an EDX system with spot analysis and elemental mapping facilities (EDAX, Tilburg, The Netherlands). Backscattered-electron images of the cross-sections were mostly taken at 20 kV accelerating voltage, at a 10 mm or 5 mm eucentric working distance, resp. Prior to SEM-EDX analysis, samples were gold coated to improve surface conductivity.

X-Ray Diffraction (XRD)

A scraping of the whitish semi-transparent degradation material was analysed by XRD, using a Discover D8 microdiffractometer with a General Area Detection Diffraction System (GADDS) two dimensional detector (Bruker AXS, Karlsruhe, Germany). The sample was applied in a little cedar oil on a Silicon zero diffraction plate. Diffractograms were acquired in reflection mode with CuKα radiation (40 kV, 30 mA). The GADDS software was used for integration and the Bruker AXS Eva software for phase identification using the PDF database.