His technique improved gradually and eventually people wanted to buy his work, which now included overtones, shading and complex designs such as landscapes. He created most of his work between 1880–1886 and is acknowledged as the inventor and possibly the sole practitioner of his art form. During his lifetime, it is thought that Clemens produced hundreds of his sand bottles but few survive today. The more complex subjects of Clemens' work ranged from steamboats, flowers, eagles, and flags and he often created custom bottles with scenes of his client's choosing. He created many of his images upside down. Upon completion, Clemens would securely stopper the bottle, and flip it right side up. The most complex of his designs could take up to a year to complete.