Alexander Calder is one of the best-known and most beloved American artists. Born in 1898 into a family of artists, he was trained as an engineer at Stevens Institute of Technology in New Jersey, but in 1923, while on the West coast of Canada, he decided to become an artist. By the fall of 1926, he left New York for Paris, then the global hub of modernity as well as tradition, fashion, pleasure and, most of all, art. Compared to the United States’ increasing isolationism, prohibition, puritanism, and racial division, the French capital offered enticing artistic liberties and freedoms. It was there that Calder became acquainted with many famous artists, including Mondrian, Picasso, Miro, Duchamp, Kertész, and Matisse, and made connections with a number of galleries that provided the perfect environment for the budding artist.
While experimenting with drawing, painting, woodcarving, and wire in the late 1920s in Paris, Calder became interested in motion. In the fall of 1929, he visited Mondrian’s studio and later recalled: “This one visit gave me a shock that started things. I suggested to Mondrian that perhaps it would be fun to make these rectangles oscillate” [1]. Revolutionary thoughts followed: “Why must art be static? You look at an abstraction, sculpted or painted, an exciting arrangement of planes, spheres, nuclei, entirely without meaning. It would be perfect, but it is always still. The next step in sculpture is motion” [2]. As a result, Calder’s signature sculptural medium would become not the traditional stone or clay, but motion: kinetics in space.
Greatly influenced by the dramatic astronomical discoveries around 1930, including the identification of Pluto as the ninth planet in the solar system, Calder started building motorized works in 1931. His first creation, now destroyed, was entitled Motorized Mobile That Duchamp Liked. In October 1931, Marcel Duchamp visited Calder’s studio in Paris and saw one of his motor-driven works, with three elements. As Calder recalled: “I had just painted it, and he was so anxious to see it move that he pushed it, and he got all full of paint [3]. I asked him what sort of a name I could give these things and he, at once, produced «mobile»” [1]. In addition to indicating something that moves, this word in French also means «motive».
Currently, fewer than 40 mobiles of similar scale are known, all made by Calder in a span of ten years. He created entire compositions with several elements rotating at different relative speed. A single cycle of these motorized sculptures would take from a few minutes to up to 45 minutes to complete. One of the largest and earliest whimsical works, Half-Circle, Quarter-Circle, and Sphere (referred to as Half-Circle from here onwards), belongs to the collection of the Whitney Museum of American Art, New York. Created in 1932, Calder titled this mobile simply by naming the shapes it comprises. The sphere, an implied form created by the intersection of two red painted disks, swings as an upside-down pendulum, while the black-painted heavy-gage metal rod that forms the half circle and quarter circle element rotates around its own axis. The white base - an essential part of the object - is the visual anchor of the work, as well as the physical support that houses the motor. The white color of the base allows the moving elements of the sculpture to be the focus of the spectator’s attention rather than the base.
Besides their physical appearance, motion is a vital part of Calder’s mobiles. The artist admitted that his motorized contraptions were not made for eternal perfection. In a 1932 interview for the New York World-Telegram, Calder reasoned his tinkering: “I had my choice between perfecting a motor for one or two things, or going on to new creations. I preferred to go on creating”. He added: “To an engineer, good enough means perfect” [2]. Hence, the mechanics inside Half-Circle’s base are strikingly imprecise. Calder’s joyful personality and his deep vein of hilarity, embodied in his figurative works, is also present in his machineries. Indeed, the motion of these gadgets often includes one or more surprise moments, such as an unexpected change of speed or an apparent collision of the moving elements. In Half-Circle, in particular, the black rod first appears to kick the side of the sphere and, then, the two elements almost crash into one another.
Acquired by the Whitney Museum in 1969, over three decades after its creation, Half-Circle has travelled and operated extensively. It functioned intermittently until 2010, when it was sent to the Art Gallery of Ontario, Canada, the last venue of the Alexander Calder: The Paris Years, 1926–1933 retrospective exhibition, after which it was no longer operational. A 2016 restoration treatment involving the mechanism revealed that almost all mechanical glitches were caused by loose bits of wood, belts, wire, and nails that were not inherent to the motor itself. The current motor, dated to 1980 and recycled from an old photocopy machine, was likely selected because it fit the cradle of the missing original motor, about which no information could be recovered. The speed of motion of the red sphere and black rod − 21 and 14 seconds, respectively - locates Half-Circle within the speed range of similar mobiles. Accuracy of the relative velocity of the spiral to the sphere is supported by one of Calder’s drawings of Half-Circle’s twin piece Double Arc and Sphere, also dated to 1932: on this drawing, the artist indicated the sphere’s swing to be slower than the spin of the spiral, and that the pulleys gear down the speed of the motor, which corresponds exactly to what is observed in Half-Circle. Moreover, in Calder’s opinion, the speed of a mobile’s motion was not a rigid rule. For instance, he recalled changing his mobiles’ speed at the 1932 Gallery Villon exhibition: “[Mondrian] said they weren’t fast enough, and when I stepped on things, he said they weren’t fast enough, so I said I’d make one especially fast to please him, and then he said that that would not be fast enough - because the whole thing ought to be still” [4]. Thus, despite the non-original motor, Half-Circle likely retained the right type and speed range of its motion; only the exact original speed of the individual elements remains, so far, unknown.
The painted surfaces of Calder’s Half-Circle posed another significant challenge. Verbal accounts and conservators’ experience through practice narrate that the artist typically painted his works with commercial household products, applying the paint straight from the can, directly onto the metal or wood, with no surface preparation or primer coat [5, 6]. He allegedly favored very matte paints and applied thin, single layers by means of a brush. According to such non-written sources, occasionally, Calder himself applied the paint or, in other cases, recommended a caretaker to restore a mobile. Orrin Riley, founder of the conservation department at the Solomon R. Guggenheim Museum and chief restorer there for more than two decades, recalled Calder giving him a bucket of red paint to repaint Red Lily Pads, the iconic mobile hanging from the museum’s spiraling rotunda [7]. These accounts attest to a long history of excessive overpainting and, in some cases, complete repainting of Calder’s works that, over the years, has prompted much debate in the art conservation world. For decades, when a paint became worn or chipped, lacunae were typically left and the entire surface would be repainted, reportedly often with the same or similar color or paint brand, as also observed on Half-Circle.
As in the case of several other Calder objects, during its over 85 years of life, the appearance of this mobile, too, has been considerably altered. Most of its surfaces are currently overpainted and, as a result, do not deliver the proper gloss, hue, and texture as originally intended by the artist. The existing thick, gleaming white paint, for instance, is far from Calder’s matte, single-layer brush application of white colors, while the heavily overpainted red of the sphere does not even remotely resemble the thinly brushed original surface. In general, the thick, rough accumulation of layers observed in Half-Circle and other works appears extremely different from the fine, thin brush marks found on Calder’s original painted surfaces, which causes the current appearance of this object to be overall inconsistent with its intended aesthetic. The above-mentioned history of overpainting and repainting of Calder’s works, along with the lack of published analytical data on his materials and techniques, provided an impetus to document, recover, and retain any extant original paints on this noteworthy early mobile. With these observations in mind, an in-depth technical study was undertaken to gain insight into the stratigraphy of Half-Circle and address any outstanding issues in preparation for an exhibition, entitled Calder: Hypermobility, held at the Whitney Museum from June 9th to October 23rd, 2017 (Fig. 1). The present article reports for the first time a comprehensive, multi-technique scientific investigation of one of Calder’s indoor motorized sculptures, Half-Circle, Quarter-Circle, and Sphere, with the threefold goal of gathering detailed information on the number and composition of paint layers in selected areas of the object; of determining whether an original layer was present underneath the white, red, and black overpaint; and of informing the development and optimization of a treatment plan tailored for the safe removal of the overpaint to uncover the original layer, wherever present.
Experimental
The extensive campaign of scientific analysis performed on Calder’s Half-Circle included both in-situ non-invasive investigations with portable instruments and removal of microscopic samples followed by analysis with benchtop equipment in the Department of Scientific Research (DSR) of The Metropolitan Museum of Art (The Met). Special attention was devoted to inspecting the paints’ composition in relation to the possible presence of an original paint layer underneath the repainting. Initially, non-invasive analysis was carried out at the Whitney Museum storage facility using a handheld X-ray fluorescence (XRF) spectrometer, in order to gain preliminary information on the elements contained in the white, red, and black paints in a selection of representative locations. Removal of fifteen samples for cross sections and loose samples led to examination with optical microscopy and analysis with a variety of instrumental techniques, including transmission and attenuated total reflection (ATR) - Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, as well as scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), with the main goal to identify the pigments, colorants, and extenders located in the various paint layers. Scrapings were also investigated with pyrolysis – gas chromatography / mass spectrometry (Py-GC/MS) for a detailed characterization of the binding media present within the stratigraphy. Experimental conditions for the analytical techniques used are reported in the following sections.
XRF – Analysis was performed using a handheld Bruker Tracer III-VTM energy dispersive X-ray fluorescence analyzer, with Peltier-cooled advanced high-resolution silver-free Si-PIN detector with a 0.2-µm beryllium (Be) window and average resolution of approximately 142 eV for the full width at half maximum of the manganese (Mn) Kα line. The system is equipped with changeable filters, and a rhodium (Rh) transmission target with maximum voltage of 45 kV and tunable beam current of 2–25 µA. The size of the spot analyzed is approximately 3 × 4 mm. Analysis was performed using 40 kV, 12.5 µA, 120-s acquisition time, and titanium (Ti) – aluminum (Al) filter, by positioning the instrument at a ≈ 1-mm distance from the artwork’s surface.
SEM/EDS - Analysis was carried out with a FE-SEM Zeiss Σigma HD equipped with an Oxford Instrument X-MaxN 80 silicon drift detector (SDD). Back-scattered electron (BSE) imaging and EDS elemental analysis were performed in high vacuum at 20 kV, on 12-nm carbon-coated samples.
Raman – Analysis was conducted using a Bruker Senterra Raman spectrometer equipped with Olympus 50x and 100x long working distance microscope objectives and a charge-coupled device (CCD) detector. A continuous wave diode laser, emitting light at 785 nm, was used as the excitation source, and two holographic gratings (1800 and 1200 rulings/mm) provided a spectral resolution of 3–5 cm− 1. The output laser power was kept between 10 and 25 mW, while the number of scans and integration time were adjusted to prevent damage from overheating and according to the Raman response of the samples examined. Spectra were interpreted by comparison with published literature and library databases available at The Met’s DSR.
FTIR - Analysis was performed with a Hyperion 3000 FTIR spectrometer equipped with a mercury cadmium telluride (MCT) detector. For measurements in transmission, each sample was crushed in a Spectra Tech diamond anvil cell and all paint layers contained in it were analyzed as a bulk through a 15x objective. For ATR measurements, each paint layer in the cross sections was analyzed individually by means of a 20x ATR objective featuring a germanium crystal. In both cases, spectra were collected in the 4000 − 600 cm− 1 range at a resolution of 4 cm− 1 as the sum of 128 or 256 scans, depending on the response of the various samples. Spectra were interpreted by comparison with published literature and library databases available at The Met’s DSR.
Py-GC/MS - Analysis was carried out on an Agilent 5973N gas chromatograph equipped with a Frontier PY-2020iD Double-Shot vertical furnace pyrolyzer fitted with an AS-1020E Auto-Shot autosampler. The GC was coupled to a 5973N single quadrupole mass selective detector (MSD). Samples of 30–50 µg were weighed out in deactivated pyrolysis sample cups (PY1-EC80F Disposable Eco-Cup LF) on a Mettler Toledo UMX2 Ultra microbalance. Samples were then either pyrolyzed without derivatization or derivatized with tetramethyl ammonium hydroxide (TMAH) before pyrolysis. Derivatization took place in the same cups as follows: 3–4 µl of 25% TMAH in methanol (both from Fisher Scientific), depending on the sample size, were added directly to the sample in each cup with a 50-µL syringe and, after 1 min, loaded onto the autosampler. The interface to the GC was held at 320 °C and purged with helium for 30 s before opening the valve to the GC column. The samples were then dropped into the furnace and pyrolyzed at 550 °C for 30 s. The pyrolysis products were transferred directly to a DB-5MS capillary column (30 m × 0.25 mm × 1 µm) with the helium carrier gas set to a constant linear velocity of 1.5 mL/min. Injection with a 30:1 split was used, in accordance with the sample size. The GC oven temperature program was: 40 °C for 1 min; 10 °C/min to 320 °C; isothermal for 1 min. The Agilent 5973N MSD conditions were set as follows: transfer line at 320 °C, MS Quad 150 °C, MS Source 230 °C, electron multiplier at approximately 1770 V; scan range 33–550 amu. For samples run with TMAH, the detector was turned off until 3 min to avoid saturation by excess of derivatizing agent and solvent. Data analysis was performed on an Agilent MSD ChemStation D.02.00.275 software by comparison with the NIST 2005 spectral libraries.