Donald Judd's "Stacks" are a key element of his artistic oeuvre, representing a significant development in the realm of Minimalist sculpture. Initially disillusioned with the traditional limitations of painting, Judd sought to explore the possibilities of three-dimensional forms existing in "real space," distancing himself from the portrayal of recognizable imagery and instead focusing on elemental geometric forms and serial order. His stacks, comprising cantilevered boxes arranged vertically on the wall at equal intervals, embody this exploration, creating a rhythmic alternation of open and closed volumes that extend from the floor to the ceiling. These works, often constructed from galvanized iron and coated in automobile paint, were fabricated according to Judd's specifications by industrial fabricators, marking a departure from traditional artistic craft in favor of a more conceptual approach rooted in industrial production​ (MOMA)​.

Judd's practice was not just about the physical manifestation of forms but also about challenging the prevailing norms of art presentation and conservation. He was a strong advocate for permanent installations, believing that the transient nature of gallery and museum exhibitions could diminish the essence of the artworks. This belief led him to purchase properties in Marfa, Texas, transforming them into the Chinati Foundation, a space where his works could be installed permanently, ensuring they were experienced in the manner he intended​ (Wikipedia)​.

One notable example from 1970, housed in The Metropolitan Museum of Art, features galvanized iron and amber acrylic sheets, illustrating Judd's innovative use of materials and color within his stacks. Judd's stacks are not only a visual experience but also a conceptual one, inviting viewers to engage with the works in a manner that transcends traditional sculptural forms​ (The Metropolitan Museum of Art)​.

Throughout his career, Judd's works, including his stacks, continued to evolve, increasingly incorporating a variety of materials and exploring different scales and complexities. His later works expanded in size and complexity, reflecting his continued interest in how artworks interact with their surrounding environment and the viewer's space. This exploration was underpinned by his steadfast belief in the autonomy of the artwork, a principle that guided his practice from his early stacks to his expansive installations at the Chinati Foundation in Marfa, Texas​ (The Art Story)​.

Judd's stacks, with their rigorous formal simplicity and emphasis on the relationship between object, space, and viewer, stand as a testament to his vision of art as an experiential and spatial phenomenon, challenging and expanding the boundaries of Minimalist sculpture.