Following seven years of research and experimentation at their Volta Laboratory, Charles Sumner Tainter, Alexander Graham Bell, and Chichester Bell introduced wax as the recording medium and engraving, rather than indenting, as the recording method. In 1887, their "Graphophone" system was being put to the test of practical use by official reporters of the US Congress, with commercial units later being produced by the Dictaphone Corporation. After this system was demonstrated to Edison's representatives, Edison quickly resumed work on the phonograph. He settled on a thicker all-wax cylinder, the surface of which could be repeatedly shaved down for reuse. Both the Graphophone and Edison's "Perfected Phonograph" were commercialized in 1888. Eventually, a patent-sharing agreement was signed and the wax-coated cardboard tubes were abandoned in favor of Edison's all-wax cylinders as an interchangeable standard format.