In the original Deskthority threadPDP_11 was selling some pretty unique keyboards, among others this Raytheon featuring glass switches.
From the listing:
This is a Raytheon 226274 keyboard that appears to be from the late 60s or early 70s. It is extremely rare, and I have been unable to find any pictures online of it. The keyboard uses Raytheon KB-SR1 switches, which are made of glass, and allow you to see the switch mechanism in action. The keycaps are of an interesting shape, which enhances the vintage look. The keyboard is contained in a metal case, and it weighs in at 7.5lbs – PDP_11.
Answering the question if it's "glass on glass, or glass on plastic?", timetoy who reposted the original pictures from 2019 replied:
It's from 1969, plastics were just starting, so I would say glass on glass! No rage banging that keyboard!
Well, taking a closer look at the switch, it has a metal stem:
Also, I had to look up this but several plastics became widely accessible in the 50s so, while today's favorite switch materials may have come later, there were various plastics around in that time – looking at the keycaps this should be pretty obvious.
However, many parts of a contemporary computer were made of glass (e.g. vacuum tubes) and maybe it was straightforward to make the switch housing from this material too.
As it turns out, Raytheon is quite a big name in high-end audio and audiophile circles so that would make sense for an expert in glass tube manufacturing.
Finally, as already told, this warehouse liquidation happened and ended in 2019 so please stop contacting the seller. ;)