Record Production

DIAMOND DISC RECORD PRODUCTION

"The production of Diamond Discs was a complex series of processes that underwent constant change and monitoring during all the years of production."
Ronald Dethlefson

The Diamond Disc record was really a two-piece product because it was necessary to produce a record core and then to overlay that core with a plastic material that could take the impression of the master mould. There were two major production processes for each record: core or powder blank formation and record pressing.

Powder Blank Formation

First, the powder blank was prepared from wood powder or wood flour together with resin binder. Its production process was similar to the present-day process for producing particleboard. Indeed, Edison powder blanks can be considered high quality, finely grained particleboards. Their thickness retarded record warpage and the blanks 'also served as sounding boards which seemed to improve audio quality.

Condensite Coating

After formation, the powder blanks were coated with a phenolic varnish that Thomas Edison called Condensite. It was invented by Edison's chief chemist, Jonas W Aylsworth and was similar to Bakelite which was invented at about the same time by Dr L. H. Baekeland. The somewhat porous powder blank absorbed a primer coat of Condensite and then one or more finishing coats were applied with a drying interval between each coat 2. Next followed a baking treatment of six hours in ovens where the temperature was slowly increased from room temperature to 2000 F.

Experiments with Production Techniques

Over the years, different production techniques were used with the blanks. In Edison's patent No 1,283,706, granted in 1918, he stated that the chemical paraphenylindiamine materially decreased the drying time of the coated blanks when it was added to the phenolic varnish in small amounts. About 1916, a mechanical varnishing machine replaced the hand -brushing of varnish. The second major production process was the pressing or printing of the records. The varnish-coated record blanks were taken from their baking ovens and allowed to cool. They were then loaded into holders, each of which contained a pair of moulds, and the holders were placed in steel racks in groups of twelve from which they were injected into the press. Thus twelve double-sided records were produced per press run or "round." Pressing time was nine minutes under physical pressure of 1000 pounds per square inch with a temperature equal to that of steam at 125 p.s.i. (see U.S. Patent No 1,411,425)

As you can imagine, the wear on moulds was intense and, therefore, Edison experimented with pre-softening the blanks within the presses for about three minutes with steam heat before physical pressure was applied This procedure seemed to reduce wear on the moulds and was described in patent No 1,369,272 which was granted in 1921.

Record Pressing

Another procedure to reduce mould wear was described in patent No 1,411,425, granted in 1922. Here Edison directed that record blanks be taken from the baking ovens in a partially-cooled or "rubbery" state. The blanks were then inserted in the presses and pressure was applied immediately. Edison stated that the former process of pre-softening the blanks within the presses drove off solvents in the phenolic varnish too qu!ckly and caused air bubbles to form on the record surface, thus giving an inferior playing surface. Another facet of the 1922 patent was the fact that physical pressure and heat were applied gradually and built up to the maximum amount. In the regular pressing process, we find that after the nine minute pressing time the records were water-cooled in their mould holders while still under moulding pressure. When properly cooled, the mould holders containing the records were ejected from the press to be sent for "knocking out" of the records, inspection and reloading. The whole pressing operation totaled twenty minutes for each "round" of twelve records and this meant each press produced 240 records in eight hours. Making Diamond Discs was slow going!

Safety and Production Problems

Production of Diamond Disc records entailed many variables, anyone of them could cause problems. For instance, the 1924 document files at the Edison National Historic Site contain numerous daily report sheets from the pressing plant in which the various problems are described. One report noted that workmen were cautioned about sweeping floors and raising dust near carts of blanks awaiting pressing. The reason for such caution, the report continued, was that there wq.s only time to clean each record blank once with a feather duster before pressing Another report mentioned that imperfections in finished records were traced to contaminated feathers on the dusters. It seems the birds that provided the feathers had dandruff! Yet another report told of granular, rough record surfaces being traced to the fact that wood flour for powder blanks had been packaged in poorly recycled burlap bags that had earlier contained sugar.
There were safety problems involved in record production too. The powder blank department burned down in 1917 Build-up of wood flour dust was a contributing cause. In the record pressing room a constant hazard was the presence of alcohol fumes given off as the records were moulded. Quality control reports in the document files for 1924 show that alcohol fumes were constantly monitored, lest the pressmen be overcome or the presses catch fire.

Courtesy of Ronald Dethlefson and Rutgers University