Edison Diamond Disc Technology
The top and bottom surfaces of the disc were molded in celluloid and then bonded to the ¼ inch molded wood-flour based core. Condensite thermosetting varnish was then applied to each side of this wood/celluloid sandwich. The disc was then cured in a heated oven to create the blank record used in the pressing process. The earliest surfaces were .22 inches, thinner than the .25 thickness of later blanks.
Although 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.
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. 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.
The formula for the record surface as well as the method of application changed in mid 1916. Edison no long bonded a celluloid sheet to the wood-flour core. Condensite was applied directly to the core. The surfaces were usually quite noisy. 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.
1910 - 1929
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.
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. Each disc was supposed to get four coats of Condensite to seal the wood-flour core and provide a smooth record surface. However many hastily-pressed records may not have the required coatings. Hence, the noisy surfaces. In 1921 the powder blank formula was changed again with china clay being substituted for much of the wood flour. China clay could be ground finer and it didn't swell due to moisture. All this helped provide smoother surfaced records. 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. Edison patented the "B S" treatment (U.S. patent 1,774,534, granted Jan. 21, 1930, applied for Jan 29, 1926). 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. rosin binder." The "B S" also made the blanks water resistant.
["B S" comes from a refinery and oil storage waste called "B S & W," Bottom Sediment & Water. In other words, SLUDGE! "B S" contains particles of fine grit, bits of asphalt, and anything that is not filtered out and is heavier than water or oil. "B S" can also be treated by filter pressing or centrifuging, and heating to recover useful burnable byproducts. source: David K.]
Fortunately, Edison continued to perfect the process. Record surfaces became smoother and quieter in the 1920's.
Domestic production of Edison Diamond Discs ceased in this time frame or soon thereafter.
References: "Edison Disc Artists & Records 1910-1929," by Wile & Dethlefson; "The Edison Disc Phonograph" by George L. Frow; and thoughts of Ronald Dethlefson.
The page was updated on February 19, 2001.