Morris Louis embarked on a phase of experimentation and innovation from 1959 to 1960, famously categorized under the theme "Themes and Variations." This period was marked by a series of works that delved into the exploration of color, form, and the fluidity of paint, showcasing Louis' mastery over his medium and his commitment to pushing the boundaries of abstract painting.

During the late 1950s, Morris Louis, along with fellow artist Kenneth Noland, was deeply influenced by Helen Frankenthaler's stain paintings, which they encountered during a visit to her studio. Frankenthaler's technique of pouring thinned paint onto unprimed canvas to achieve translucent color veils significantly impacted Louis. This approach resonated with Louis and led him to develop his unique method of applying extremely diluted paint to canvas, allowing it to flow and create effects reminiscent of translucent veils. This technique was not only a testament to Louis' innovative spirit but also aligned with the Color Field movement's emphasis on the flatness of the picture plane and the exploration of pictorial space through color​ (Wikipedia)​.

The "Themes and Variations" series was a pivotal moment in Louis' career, highlighting his exploratory approach to color and composition. One notable work from this period is the "Aleph Series," in which Louis poured linear sequences of thinned paint onto the canvas. These works seemed to simultaneously converge towards and branch out from the center, creating a dynamic interplay of movement and stillness, depth and flatness. The "Aleph Series IV," for example, demonstrates this technique with a composition that appears to both radiate from and recede into the canvas's center, embodying the series' exploration of color and form's ephemeral qualities​ (Empire State Plaza & Capitol)​.

This phase of Louis' work is reflective of the broader ambitions of the Color Field painters, who sought to dissolve the barriers between the paint and the canvas, creating immersive color experiences that engage the viewer's perception in profound ways. Through "Themes and Variations," Morris Louis solidified his place in art history as a pioneering figure who explored the possibilities of color and abstraction with unparalleled depth and sensitivity. His work from this period continues to inspire and influence artists and art enthusiasts alike, serving as a testament to the enduring power of abstract expression.