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I have noticed something weird about the Edison Diamond Disc’s audio quality. Why did it seem to just get worse around 1917 or so? What happened?

The diamond discs produced during WWI have a high level of hiss, reaching the unbearable on some pressings. This is due to lack of some of the materials utilized in the playing surface. I never noticed any degradation in the recording quality, though. It is quite the opposite: the quality of the Edison recordings improved over the years until the end of the acoustic era.

CarlosV wrote: Sun Jun 15, 2025 4:58 pm The diamond discs produced during WWI have a high level of hiss, reaching the unbearable on some pressings. This is due to lack of some of the materials utilized in the playing surface. I never noticed any degradation in the recording quality, though. It is quite the opposite: the quality of the Edison recordings improved over the years until the end of the acoustic era.

What materials were supposed to be used and what did they stop using around 1916-1918 due to WWI?

MisterGramophone wrote: Sun Jun 15, 2025 5:36 pm
What materials were supposed to be used and what did they stop using around 1916-1918 due to WWI?

Stearine is the main lacking material and was imported from Germany. It was applied to reduce hiss.

Phenol
The material that became difficult to get was Phenol the German chemical industry was probably the largest source at the time but all European sources would have been diverted to make Lyddite a trinitrophenol explosive.
Edison set up a plant in a few weeks to make it and West Orange this may have had quality and quantity limitations.
However a believe that the number of coats of varnish may have been reduced in this period probably leading to the substrate surface powder blank surface being heard through the thinner surface.
There are reports of other quality control problems involving the sugar from used sacks that contained the wood flour for the cores and chicken dandruff form the feather dusters used to clean the varnish.

Steaine or Stearin
this used to make wax cylinders and disc master blanks
But there probably was no shortage of it in the USA as it was derived from beef tallow.

recordmaker wrote: Mon Jun 16, 2025 5:30 am Steaine or Stearin
this used to make wax cylinders and disc master blanks
But there probably was no shortage of it in the USA as it was derived from beef tallow.

Edison patented the use of stearin to preserve the surface of diamond discs, see attached. Its shortage was reported at the WWI period.

You may find my comments in this thread relevant. It's an explanation of the pressing date codes used on Diamond Discs during the WWI years:

viewtopic.php?t=11036&hilit=date+code

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Edison patented the use of stearin to preserve the surface of diamond discs, see attached. Its shortage was reported at the WWI period.
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This was something I was aware, but not that it was patented. Possibly a thin waxy polish applied to the discs would have needed very little raw material per record compared with the varnish and powder blank.