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Oil Paintings by Georgia O'Keeffe

The Artist

Georgia O’Keeffe has remained for almost seven decades a major figure among the American modernists. O’Keeffe was one of the first American artists to practice pure abstraction and created her own individual style of painting, which synthesizes the formal language of modern European abstraction and the subjects of traditional American pictorialism. She produced an unusually cohesive body of work, based on a selected number of themes, which evolves her working process of artistic self-evaluation and reinterpretation.

The Investigation

In collaboration with the Georgia O’Keeffe Museum, the Center for Scientific Studies in the Arts is investigating soap formation on oil paintings produced by Georgia O’Keeffe. This research will link the microscale formation of metal carboxylates soap protrusions on paintings by the artist Georgia O’Keeffe to long-term macroscopic changes to these works of art.

The Goal

Our research aims are: 1) the chemical characterization of the soaps and the conditions that led to their formation, and 2) to develop a protocol to monitor the occurrence and extent of soaps protrusions in oil paintings at the macro-scale. To this end, an open-source and web-based image-analysis tools will be developed to aid conservators in the long-term monitoring of soap protrusions and other alteration phenomena.

The Process

High-resolution analytical tools will be used to characterize metal carboxylate soaps in O’Keeffe’s oil paintings. With access to O’Keeffe’s commercial paint tubes and color paint-outs housed at the O’Keeffe museum. We hope to correlate these specific paint formulations on the occurrence and distribution of protrusions on the artist’s paintings.

Using samples of the soaps, their chemistry will be characterized to better understand the factors contributing to their development. At the same time, non-invasive imaging techniques will be used to detect, map and monitor the micro-eruptions and their evolution over time.

The Impact

We expect this study to provide us with a better understanding of soap formations in Georgia O’Keeffe paintings and to make informed decisions regarding their conservation. In addition, this research will have far-reaching implications on the conservation practices of paintings. To this end, we will develop an open-source software and image-analysis tools to aid conservators in the long term monitoring of soap protrusions, extending the benefits of the research beyond the O’Keeffe collection to many others similarly affected paintings around the world.

Photometric stereo by UV-induced fluorescence

The use of fluorescence emission as a light source for PS of painted surface enable more accurate, precise, and repeatable shape measurements. The use of UV-induced fluorescence presents two benefits: 1) the calculated albedo aids in the accurate detection and segmentation of the protrusions and 2) information on the UV-induced fluorescence response of the protrusions is simultaneously collected in the visible range, which can contribute to materials differentiation and characterization.

For this purpose, a set of pictures are taken of the painting with a fixed camera, each shot under a different angle of UV light illumination. Using both the albedo and shape information, two data analysis methods were tested and compared to investigate the occurrence and distribution of protrusions in different colored areas. This method provides quantitative information on the protrusions by detecting all visible protrusions within the investigated region.

X-ray fluorescence imaging

The XRF map allows to obtain elemental distribution images, this non-invasive analytical technique provides a more clear understanding of the painting layers composition. The images obtained reveal the spatial distribution of pigments on or beneath the paint surface.

The XRF performed on Pedernal as a case of study, exhibit a lead elemental distribution map that indicates that lead white was likely mixed with the colored pigments in varying proportions to produce lighter tonalities. The regions that are richest in lead correlate with the areas with a higher occurrence of protrusions. These observations suggest that the specific type of lead white paint formulation in tubes employed by O’Keeffe and its proportion play a critical role in the development of protrusions

Correlating protrusions with paint composition

In order to visualize the protrusions within the paint fragment cross sections and to identify and localize their inorganic components, SEM-EDX was used. Images were taken in variable pressure mode to minimize charging of the paint.

In the cross sections, protrusions can be identified by its darker color and for having a smooth texture. BSE images allow the characterization of different phases in the protrusion, with a phase of heavier elemental composition in the center with some semi-crystalline metal soap aggregates. While the EDX analysis allows the elemental characterization of the samples, the color coded mapping data shows that protrusions are lead rich.

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