Arp began exploring the potential of sculpture in the round in the early 1930s, with plaster as his preferred medium. After establishing a basic form, he would apply plaster in layers with a spatula. Such additions would be filed and sanded, and this alternation between layered applications of plaster and the abrading of irregularities created surfaces of enormous subtlety. The resulting swells, dips, and sudden intervention of sheared planes slicing through the plaster confounded expectations of what other sides of the sculpture might look like, a physical manifestation of the unpredictability Arp prized in nature. In a 1960 interview, he explained his sculptural practice as an intuitive, almost unconscious process:

This is the mystery: my hands talk to themselves. The dialogue is established between the plaster and them as if I am absent, as if I am not necessary. There forms are born, amicable and strange, that order themselves without me. I notice them—as sometimes one notices human figures in clouds.

Once Arp had completed a sculpture in plaster, a mold would have been taken, from which a plaster cast could be made. Such a cast represented Arp’s vision of the work—a conceptual understanding of art that prioritized the artist’s idea over the handmade physical result. Preserved in casts, the initial, finished plasters then became material for new sculptures. Indeed, Arp’s plasters were transitional objects that played a variety of roles. He exhibited them (especially before he began casting regularly in bronze), and he kept multiples of them around his studio as inspiration and as material, cutting them up and even leaving them outside, exposed to the elements. Later in his career, he also made enlarged versions of his sculptures by first scaling them up in plaster.

In 2018, the Nasher Sculpture Center presented The Nature of Arp, a comprehensive exhibition of the artist’s work in all mediums. Information about The Nature of Arp and its accompanying publication can found online in past exhibitions.