Invention rarely stops when the inventor introduces a new device. Thomas A. Edison and his team worked to improve his electric lighting system for some years after the initial introduction in 1880. This lamp shows changes made after about ten years of labor aimed at lowering costs and increasing production. The simplified base required little material; the diameter and thread-pitch are still used today. The filament was changed from bamboo to a treated cellulose, based on an invention by English chemist Joseph Swan. The bulb was probably free blown by Corning Glass Works, but would soon be replaced by a bulb made by semi-skilled laborers blowing glass into iron molds. The cost had dropped from about $1.00 per lamp to less than 30¢.