The paper describes the near-surface microstructure of artistic frescoes and compares the traditional fresco technique in which the pigments are applied on a fresh lime intonaco with the more recent technique in which the lime intonaco is replaced by a fresh cement plaster. The study is performed on artworks produced at different periods: one Roman fresco fragment dated from the first century CE, samples from a Renaissance Botticelli fresco and two works by a 20th century artist, Henri Marret, one on a lime intonaco and the other on a cement plaster. A special attention is given to the nature of the pigments used, to their position and adhesion process near the surface and to the colorimetric analysis of the pieces. The characterization of the different objects (performed by optical microscopy, scanning electron microscopy and microanalysis, colorimetric measurements and X-ray diffraction) gives full information on the influence of the artist's technique on the adhesion process and durability of the coloured decoration. It is proved that fresco painting on fresh cement, although considered at the beginning as not as efficient as fresco on lime, leads to a similar mechanism of pigment adhesion and probably to a similar durability. Copyright © 2014 John Wiley & Sons, Ltd.

An exceptionally perennial surface artwork: fresco on lime or on cement

The modern decoration of the Saint Nicolas de Myre Church at Semsales (1924–1926), is the first by renowned Italian artist Gino Severini in Switzerland. Following archival research and visual examination, the materials and the techniques used by Severini for the wall paintings of this church were examined through a multi-technique analytical approach that included both non-invasive and invasive investigations. Archival research revealed lists of some of the materials purchased for the church and notes of the artists. In situ investigations included imaging methods and point analyses (X-ray fluorescence and reflection FT-IR spectroscopy). Based on non-invasive results, a limited number of representative samples were collected for laboratory invasive analyses (SEM-EDS, FTIR-FPA imaging, μ-Raman and GC-MS) to characterize the stratigraphy and the composition of the paintings. Results were coherent with artist’s notes and revealed protein-based binders, i.e. animal glue and casein, exclusively on the Trinity mural (in the apse) confirming the use of a secco technique. All the other wall paintings analyzed at Semsales are painted without the use of organic binders. These findings, integrated with archival researches and the visual examination by conservators, provided significant insights into the materials and techniques used by Gino Severini in his first Swiss murals.

The Characterization of the Materials Used by Gino Severini in his 20th C Wall Paintings at Semsales in Switzerland

In 1932 David Alfaro Siqueiros was commissioned to paint a monumental mural on the second-story exterior wall of the Plaza Art Center in downtown Los Angeles. Measuring approximately eighty feet long by eighteen feet high, the mural was to depict a vision of Mexico as a land of plenty, where the fruits of the land fell, freely into the hands of the people. Instead, Siqueiros painted a scene of pre-Columbian ruins with sculptural elements, in which the central figure was a crucified peasant surmounted by an American eagle, with sharpshooters taking aim at the eagle from an upper corner of the scene. Entitled América Tropical, the mural is considered one of the most important examples of Siqueiros’s work in the United States, and is one of only two surviving murals he painted in this country. In the early 1930s, however, the subject matter was highly controversial, and the section showing the sharpshooters was whitewashed immediately. Within just a few years, the entire mural was whitewashed and left exposed to the elements. It was neglected and all but forgotten until the 1960s, when the Chicano mural movement sparked a growing interest in Mexican art by artists and art historians. One art historian in particular, Shifra Goldman, led the effort for the conservation of the mural, engaging conservators and a filmmaker to document it in the early 1970s; she continued to pursue support for its conservation over the next twenty years. By the time the mural was rediscovered, much of the primary information about its creation had been lost. When Siqueiros passed away in 1974, only a few of his preliminary sketches of the mural remained as documentation. Because he experimented with a wide variety of materials and techniques throughout his artistic career, scientists and conservators working on the mural were left with numerous unanswered questions about how it was made. Since the late 1980s the Getty Conservation Institute (GCI) has partnered with the City of Los Angeles to study and to conserve the mural. The research team took a two-pronged approach, combining scientific investigation and historic research to better understand the materials and techniques used by Siqueiros in order to reconstruct how the mural had been executed. This first wave of research has, in turn, informed the conservation treatment and critical interpretation of América Tropical, with the aim of making it once again accessible to the public.

Conserving and Presenting Siqueiros’s

While living in Los Angeles in political exile in 1932, Mexican artist David Alfaro Siqueiros painted Amirica Tropical. The mural, 24 meters long and five meters high, is painted on the exterior south-facing wall of the Italian Hall building on Olvera Street, part of the historic monument of El Pueblo de Los Angeles. For this mural, Siqueiros used an experimentalfresco technique in which he painted on fresh cement using an airbrush. Shortly after its execution, the mural was covered with white paint because of its controversial political message. The mural’s exposure to harsh environmental conditions, under direct sunlight and heat as well as the painting technique used, resulted in its deterioration. Since the late 1980s, the Getty Conservation Institute has been involved in a project to conserve the only surviving public mural by Siqueiros in the United States. In order to develop an appropriate conservation treatment it was necessary to understand the causes of its deterioration through the study of the original materials and the painting technique used, and the history of the mural. In this article, historical information and scientific evidences are combined to discuss Siqueiros’ innovative technique -fresco on cement - and the mural’s deterioration. Contemporary and historical sources provide information on the materials and the technique used in this mural; but give also contradictory evidences regarding the type of paint used. Scientific investigation was carried out on samples of the mural to identify the materials used to paint America Tropical. The pigments were identified using polarized light microscopy and x-ray fluorescence analysis. The identification of the binder was carried out using Fourier transform infra-red spectroscopy, organic elemental analysis and gas chromatography. Scientific investigation, in particular infrared analysis, seems to suggest that cellulose nitrate was the principal component of the binder. The deterioration of the mural is discussed in the light of these results.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400364454

A. Parker

Papers

Original technique of the mural América Tropical by David Alfaro Siqueiros