What are these disds made of??

[prestok10]

I have some 12" NOS blank discs I picked up in a bundle on Ebay. They have yellow labels that say "National Hollywood Recording Disc" on them and the disc itself is a kind of a dark red color. They are very shiny. The material seems very hard and so they are difficult to cut, which may also be due to age. Anybody have any clues?

[tape]

I have similar discs from wilcox gay - my best guess is that is standard laquer, hardend over time.
I have also seen blue discs.

There is somewhere here a recipe for soften up old laquers....

[sat159p1]

I have that discs too, it doesn't look like lacquer. Deafinitely something different. I planned to measure them (in chemical way) but still not enough free time

A.

[tragwag]

maybe it's a colored cardboard substrate that makes it seem so different?

[tape]

they have a metal backing...