Edison Diamond Disc Surface Dimples Cause?

[Marc Hildebrant]

Group,

On some Diamond Discs, I can hear a low frequency thump once a revolution, caused by a slight dimple or thumbprint in the surface. The sound does not reproduce on an Edison Phonograph, just on a current modern system.

You can see the defect if you glance at the record surface held at an angle.

Where did the defects come from? In the master mold or with use?

Marc

[recordmaker]

Not exclusive cases but the Edison disc production department at times had specific causes for this that took some time to track down.(George Frows book on Diamond discs I think quotes one of these ) The wood flour in one of the core material formulations was sent to the works in reused sugar sacks and the sugar residue was effectively cooked in the 20 min pressing time of the disc molds and caused some of this type of problem. At another time surface defects were discovered to be due to the use of feather dusters that remove dust from the varnished surfaces between the varnishing of the layers prior to pressing contained chicken dandruff.
The quality control on this process seemed more difficult than that for shellac solid stock pressing.
also the bonding of the stamper to the thick backing with solder can be a problem and Edison needed a lot of molds to make a decent number of copies of an one record compared with shellac record stampers.

[Marc Hildebrant]

Recordmaker,

Thanks for the information. Is there a source for more information?

Marc

[recordmaker]

I understand a lot of these internal reports are at the Edison Site archives at West Orange I assume. I don't know what is available publicly without visit as a researcher. These are mentioned by George Frow in his book on the Edison Diamond Disc Phonograph which was researched the old fashioned way on his visits to the archives at west orange in the 1980s. The Raymond Wile books about diamond discs also have odd details from the same source.
I will have to look again but significantly the Edison hired a new technical manager in the 1920/21 who went through everything in detail and oversaw the black label to white label paper transition.
For example Edison went back to gold sputtering for the discs 1912 and this made processing the master take several days in the new methods that were set up later it was possible to go from recording to finished record in 2 or 3 days and they did advertise this for the record "April Showers" being recorded in New York and 5 days later being delivered by plane and played ( for dancing to ) in San-Francisco.