I collect antiques and worked in the paint and chemical industry before I got old and stupid. These used frit ( glass chunk ) to illuminate at night.
I drive pretty slow these days. I'd have assholes behind me honking the horn every time I went somewhere.
........Learn something new everyday if you keep your mind open. I knew they used pulverized glass, but I never knew it was called "frit".......I'm enlightened, not illuminated, but enlightened.
I could be wrong on the terminology as this was before my time but my career was in coatings and chemistry for metals. Porcelain is melted glass called frit. I assume this application used larger chunks and did not fully melt it to produce refraction. A guess as to the process.
I thought beeping horn to pass was the thing to do on a two lane road? Chuck Berry Maybellene song, " A Cadillac pulled up to one hundred and four The Ford got hot and wouldn't do no more It done got a cloud and started to rain I tooted my horn for the passin' lane.. I think I've passed two cars in the last 55 years; I swear they floor it when I try to go by!