In 1905 Edison perfected this "Double Hairpin" lamp design by forming his carbon filament in an electric furnace. In this way he created a much more efficient filament and lamp. This new lamp was the first to be called the "Edison GEM" lamp. This first GEM design contained a filament which was actually 2 single hairpin filaments connected in series to give it the proper electrical resistance for 110 to 120 volts. However, like the tantalum filament lamp, this "Double Hairpin" lamp was soon overtaken by filament design innovations leading up to the Edison tungsten lamp in 1907, and then the Edison Mazda tungsten lamp late in 1909. Also in 1909, the double hairpin GEM gave way to the one piece filament GEM, and the double hairpin was discontinued forever. The series wired double hairpin filament Edison GEM lamp was on the market for only a few short years and is, therefore, a rare post-1900 incandescent lamp collectable.