Working with sand, stylus, and concrete rather than paint, brush, and canvas, a Colorado artist has given the art of mural decoration a new twist. Vincent O'Brien is the artist and concrete murals are his twist. O'Brien murals range from the huge exterior wall piece he did for a university professor's home to the smaller and often more intricate interior murals he has done for a Denver insurance company. The murals O'Brien created for Denver's Security Life Insurance Company were first sculptured in an oil-based clay. The concrete slabs then were cast directly from the clay molds. An attempt to achieve greater delicacy and detail prompted O'Brien to try the clay forms. As in the sand molds, designs had to be developed in negative form so that concrete casts would be positive. Molded depth is generally less than one-half of an inch. After a week's curing, the forms were stripped and the slabs sealed with an acrylic-based masonry paint. The paint, in paste form, was rubbed on with rags, then the one and one-fourth inch thick, reinforced slabs were mounted on one inch thick composition board, fitted in place on the wall like a giant jig-saw puzzle.