References: 'Edison Disc Artists & Records 1910-1929,' by Wile & Dethlefson 'The Edison Disc Phonograph' by George L. Record surfaces became smoother and quieter in the 1920's.ĭomestic production of Edison Diamond Discs ceased in this time frame or soon thereafter. rosin binder.' The 'B S' also made the blanks water resistant.įortunately, Edison continued to perfect the process. Edison stated in the patent, '.a blank formed of my improved material is substantially perfectly smooth with all the fibres and other particles of the filler entirely covered with the B.S. Edison patented the 'B S' treatment (U.S.

The final change to the powder blank came in the mid-1920's when a petroleum derivative called 'B S' was mixed with the core ingredients to bond them together tightly. All this helped provide smoother surfaced records. China clay could be ground finer and it didn't swell due to moisture. In 1921 the powder blank formula was changed again with china clay being substituted for much of the wood flour. However many hastily-pressed records may not have the required coatings. Each disc was supposed to get four coats of Condensite to seal the wood-flour core and provide a smooth record surface. Ron Dethlefson, a source of accurate Edison and Pathé information, suggests that the surface noise problem was compounded by the need to press discs in ever greater quantities in the post-World War I spending boom. The formulation of the disc core and surfaces was the source of considerable trouble particularly in the early years (1910 - 1913) and during/after World War I. It is thought that particles from the record core often bubbled up to the surface during the pressing process thus causing some of the noise. Condensite was applied directly to the core. Edison no long bonded a celluloid sheet to the wood-flour core. The formula for the record surface as well as the method of application changed in mid 1916. However it was later determined that the presence of gripper marks on the outside edge of these recordings indicates that Edison was still using celluloid. It was thought that Edison may have begun applying the condensite directly to the wood-flour blank rather than to a celluloid sheet in 1914. 25 thickness of later blanks.Īlthough these 'celluloid + condensite' surfaces suffered lamination cracks caused by water penetration or vapor penetration of the wood-flour based blank, these surfaces were the finest of all the Edison discs until the 1920's when manufacturing improvements made smooth surfaces possible again. The disc was then cured in a heated oven to create the blank record used in the pressing process.

Condensite thermosetting varnish was then applied to each side of this wood/celluloid sandwich. The top and bottom surfaces of the disc were molded in celluloid and then bonded to the ¼ inch molded wood-flour based core.

Edison diamond disk