45th Annual Meeting – Paintings Specialty Session, June 1, “The Conservation of Alexander Calder’s Last Work Mexico #3: The cross-disciplinary treatment supported by SEM and TEM paint cross section analysis using focus ion beam (FIB) sample preparation,” by Sara Wohler and Ralph Weigandt

Author Sara Wohler discussed the fascinating history of Alexander Calder’s airplane model, Mexico #3, the last work he completed before his death, and then presented the conservation treatment of the model. Author Ralph Weigandt then discussed the technical analysis of the paint film on the airplane.  This presentation served as a fun continuation of the painted airplane theme, following Lauren Horelick’s May 30th talk “When an Airplane Acts like a Painting: Applying Established Conservation Methodologies to Ephemeral Aircraft Materials.”


Wohler described the beginning of Alexander Calder’s airplane-making career: In 1972, New York advertiser George Gordon approached Calder with the idea of painting an full-scale airplane.  Calder loved the idea, as it would combined his experience in kinetic art and his background in engineering.  Gordon paired Calder with Braniff International Airways, and Calder created the designs for two airplanes: Flying Colors of South America and Flying Colors of the United States. These were both tremendous public successes.

^Braniff International Airways employee ceremony, 1975, with Flying Colors of the United States.

The author then described the process in which Calder painted the planes: He began by experimenting with designs on several 1/25-scale Westway Aircraft Models.  The chosen design from the model was then scaled up using graph paper that was attached to the full-size airplane.  Calder and his team then used pounce wheels to poke holes through the design on the graph paper, and black spray paint was applied through the pounce holes.  The graph paper was removed, and the paint colors were spray applied by a Braniff team.  Calder supervised the entire process, and hand-painted the engine necelles during the spray process.

Then the author described the artistic process for the model Mexico #3. In 1976, Braniff commissioned a third plane from Calder, this one to celebrate the great relationship between the U.S. and Mexico.  The author provided amazing historic film footage of Calder painting the Mexico #3 model plane.  She noted that the plane itself was made of fiberglass, and Calder created his design using gouache. On November 11, 1976, Calder completed and signed the work, and tragically, passed away later that evening.  Although the design was completed, Mexico #3 was not transferred to an airplane, as Calder was no longer alive to approve of the final result.

^Calder painting the Mexico #3 model.


The model airplane was brought to Kuneij Berry Associates, Chicago, for conservation treatment. Through examination, the author found that the fiberglass model airplane had two priming layers, blue and grey, and a final, even, white coating. Calder painted onto the proprietary white surface using gouache, possibly that he made himself. While the airplane was quite dirty and structurally had sustained a few losses, the treatment was relatively straightforward.

The plane was in poor aesthetic condition; it had previously been displayed in a planter with dirt and plants around it, exposing it to both dirt and moisture. Fortunately, the gouache paint layer was generally in good condition and intact, aside from a few abrasions.  The synthetic varnish layer, which had protected the gouache layer, was covered in surface dirt and grime.  The plane was first surface cleaned with deionized water and PVOH sponges, but a lot of the dirt remained embedded in the varnish.  The synthetic varnish was removed with aromatic solvents.  Care was taken to only thin the varnish on top of the gouache paints, as the paints were sensitive to aromatic solvents.

^Detail of the varnish removal, cleaned (left) and with remaining varnish (right).

Structurally, the plane had suffered a few chips to its wings and there were a few areas of flaking paint. The flaking paint was consolidated with Paraloid B72. To recreate the tips of the wings that had been chipped away, molds were made of Elastosil M4600 A/B and cast using Milliputti. The cast pieces were sanded and adhered to the wings using Paraloid B72.

Shallow losses in the white priming layer were filled and inpainted simultaneously with Golden MSA colors. Losses in the gouache colors were then inpainted with QoR watercolors.  The model was then sprayed with a few, light, protective layers of RegalRez 1094. After the successful treatment, it was recommended that the painting be displayed in a new, more environmentally stable location.

^Sara Wohler inpainting Mexico #3.

Technical Analysis

The technical analysis of Calder’s gouache paint was carried out by Ralph Weigandt, who is currently the primary researcher on the collaborative National Science Foundation (NSF-SCIART) grant with the University of Rochester’s Integrated Nanotechnology Center to advance the scientific understanding and preservation of daguerreotypes. The authors carried out technical analysis of the gouache paint in order to better understand Calder’s materials and techniques, potentially inform the conservation treatment, and to pioneer the use of Focus Ion Beam (FIB) milling for SEM-EDX analysis and PLM examination on paint films.  Through Transmission Electron Microscopy, SEM-FIB allows for the elemental analysis of paint layers at the nanometer scale!

Weigandt explained in depth about the sample preparation process, the Focus Ion Beam milling of the larger sample into the much smaller (~12 um x 0.5 um) cross-section, the comparison between traditional SEM-EDX spectroscopic elemental analysis and mapping vs. the Transmission Electron Microscopy and associated SEM-EDX elemental analysis and mapping capabilities.  In essence, the FIB milling and TEM allows for highly precise, high resolution elemental analysis and mapping, allowing scientists and conservators to see the inorganic composition of individual pigment particles.  A poster from University of Rochester graduate student So Youn Kim outlines the project with excellent photographs and illustrations.

In the end, the elemental analysis did not contribute greatly to the decision-making process of the treatment, but did provide excellent information about Calder’s painting techniques and materials for Mexico #3, which can inform a discussion about his art-making process for this piece and his art in general.  It is clear that this Focus Ion Beam technique coupled with Transmission Electron Microscopy and SEM-EDX elemental analysis is an exciting analytical technique that will be extremely useful in the precise identification of inorganic pigments, fillers, etc., in paint films. Furthermore, it is great to see yet another example of private conservators working with scientific departments at universities (or elsewhere) to investigate materials of cultural heritage objects!

One thought on “45th Annual Meeting – Paintings Specialty Session, June 1, “The Conservation of Alexander Calder’s Last Work Mexico #3: The cross-disciplinary treatment supported by SEM and TEM paint cross section analysis using focus ion beam (FIB) sample preparation,” by Sara Wohler and Ralph Weigandt”

  1. (Morgan) This thoughtful, thorough, and yet concise, synopsis of Sara Wohler’s and Ralph Wiegandt’s presentation on the conservation and scientific analysis of Alexander Calder’s 1976 Braniff airplane model, Mexico #3 succinctly captures the essence of Calder’s artistic collaboration with Braniff Airways in the Flying Colors project, the preservation of the authentic model, and the benefits of the Focus Ion Beam technique coupled with Transmission Electron Microscopy and SEM-EDX elemental analysis for those who were not able to attend. The post also rightly pointed out the value of conservators in private practice working in collaboration with universities and other scientific research facilities.

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