Sandra Zetina

The Grolier Codex: A Non Destructive Study of a Possible Maya Document using Imaging and Ion Beam Techniques

The Grolier Codex has been a controversial document ever since its late discovery in 1965. Because of its rare iconographical content and its unknown origin, specialists are not keen to assure its authenticity that would set it amongst the other three known Maya codes in the world (Dresden, Paris Codex and Madrid Codex). The document that has been kept in the Museo Nacional de Antropologia in Mexico City, after its exposure in 1971 at the Grolier Club of New York, has been analyzed by a set of non-destructive techniques in order to characterize its materials including paper fibers, preparation layer and color compositions. The methodology included UV imaging, IR reflectography and optic microscopy examinations as well as Particle Induced X-ray Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) using an external beam setup for elemental analysis. All the measurements were carried out at 3MV Pelletron Accelerator of the Instituto de Fisica, UNAM. The aim of this work is to verify if the materials in the Grolier Codex match those found in other pre-Hispanic documents. From the elemental composition we concluded that the preparation layer shows the presence of gypsum (CaSO4), color red is due to red hematite (Fe2O3) and black is a carbon-based ink. These results agree with previous analyses carried out by Scanning Electron Microscopy (SEM-EDX) on few samples. However, the presence of Maya Blue in the blue pigment cannot be assured. The examination using UV and IR lights shows homogeneity in the inks and red color but dark areas that contain higher amounts of K in the preparation layer. This paper discusses the results obtained for the UV-IR examinations and the elemental analysis. A comparison with other studies on pre-Hispanic and early colonial codex is presented.

A Hydrodynamic Instability Is Used to Create Aesthetically Appealing Patterns in Painting

Painters often acquire a deep empirical knowledge of the way in which paints and inks behave. Through experimentation and practice, they can control the way in which fluids move and deform to create textures and images. David Alfaro Siqueiros, a recognized Mexican muralist, invented an accidental painting technique to create new and unexpected textures. By pouring layers of paint of different colors on a horizontal surface, the paints infiltrate into each other creating patterns of aesthetic value. In this investigation, we reproduce the technique in a controlled manner. We found that for the correct color combination, the dual viscous layer becomes Rayleigh-Taylor unstable: the density mismatch of the two color paints drives the formation of a spotted pattern. Experiments and a linear instability analysis were conducted to understand the properties of the process. We also argue that this flow configuration can be used to study the linear properties of this instability.

DAVID A. SIQUEIROS: HIS MODIFICATION OF OIL- AND CELLULOSE NITRATE-BASED PAINT AND HIS ADVOCACY FOR INNOVATION, 1931–1949

Abstract Although the use of cellulose nitrate paint by David A. Siqueiros (1896–1974) is well documented, when and how he used it is not well established. This article focuses on a technical examination of six paintings Siqueiros made between 1931 and 1949. The paintings analyzed come from two collections: Museo Nacional de Arte in Mexico City and The Museum of Modern Art in New York. Findings presented here show that Siqueiros did not use cellulose nitrate for a painting he made in 1933, despite having made that claim decades later. Rather, evidence indicates Siqueiros used it in Mexico City just prior to his trip to New York in 1935 where he established a workshop to further explore innovation in painting technique and focus especially on ways to paint without a brush. Examination of a small work from 1936 or 1937 by Jackson Pollock (1912–1956), who attended the workshop, confirms he also experimented with the medium. Afterwards, in 1939, Siqueiros again altered his technique and materials in a way to suggest that rendering specific details in his paintings was more important than being restricted to the innovative “brush-free” effects developed in the workshop.

Characterization of commercial artists’ acrylic paints and the influence of UV light on aging

ABSTRACT A large part of Mexican artistic heritage was created with artists’ acrylic emulsion paints, so it is crucial to investigate their composition, behavior, and decay. Acrylic films are complex chemical systems combining organic and inorganic compounds; therefore, the degradation studies require a variety of techniques. We characterize three acrylic films before and after ultraviolet aging. The relative composition of the polymer matrix was studied by nuclear magnetic resonance, pyrolysis—gas chromatography—mass spectrometry and direct analysis in real time mass spectrometry with direct analysis in real time. The inorganic compounds and surfaces were characterized by microscopic techniques, such as digital microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and micro X-ray diffraction. The combined use of these techniques proved to be effective for an in-depth study of the acrylic painting degradation process. The main results were the gradual degradation for the organic surfactant and the loss of inorganic aggregates (talc and carbonates), that led to the disruption of the paint film, which points out the importance of studying the role and interaction of all compounds.