He is best known for his highly detailed paintings on wood panels, combining an array of unorthodox materials suspended in a thick layer of clear, epoxy resin. Tomaselli's paintings include medicinal herbs, prescription pills and hallucinogenic plants alongside images cut from books and magazines: flowers, birds, butterflies, arms, legs and noses, which are combined into dazzling patterns that spread over the surface of the painting like a beautiful virus or growth. He uses an explosion of color and combines it with a basis in art history. His style usually involves collage, painting, and/or glazing. He seals the collages in resin after gluing them down and going over them with different varnishes.