Berthot began his career making abstract paintings in the minimalist tradition. He would apply a thick painterly surface to large shaped canvases that were seen to employ the reductive means of minimalism, but expressing instead of restraining emotion.Despite its simplicity of means, his work was said to deal "more in feelings than in analysis."Painted in 1969, "Lovella's Thing" is a good example of his style at this time. Shortly before his death, Berthot explained the way in which it evolved: "With Lovella's Thing I originally thought of painting the middle a flat, blank color, but when I got into it, putting down a lot of acrylic washes, I just started to paint it in a more felt way. So it became a kind of dialect between something very concrete and something very felt. I liked the blunt presence the shape had on the wall and then penetrating the surface in the middle in what I suppose could be called a Rothkoesque kind of way."
In the mid-1970s Berthot's style evolved. His work continued to have a painterly, lyrical quality, but he added bright colors to the muted palette of earlier work and introduced rectangular bars and ovals into canvases that were now simple rectangles.Regarding the bars, he later said that he worked to uncover the tension points, or focal points, that were inherent in the vertical and horizontal axes of a grid. He said he sought "a balance between the object and the opening," and thereby "to gradually achieve balance between my two influences: the systemic and the felt." "Yellow Bar With Red," of 1977 is typical of paintings in this period. Another well-known painting from this period, "Walken's Ridge," 1975-1976, is somewhat unusual. Although a pure abstraction, it has the size and shape of Monet's Water Lily paintings—14 feet wide in two equal sections— and has, as Berthot said, the feel of a landscape