Drawing from the ceramic technique of slip casting, Mackenzie began using molds to cast liquid acrylic, a relatively new kind of paint at the time. Staining fiberglass cloth, Mackenzie then laid the cloth on a mold and saturated it with clear acrylic. Once dried, he peeled the resulting skins of paint from the mold and hung them from the wall with pushpins. Eventually he applied them to canvas. This inventive technique of cast painting utilized Rhoplex (a water-based acrylic emulsion), with which he eventually produced large-scale works. His paintings using this method were included in the important 1971 Oakland Museum of Art exhibition “Off the Stretcher.”