i think Dan would no more about finishes on my three thorns ,i know i show know but honestly i don't.
As I recall, Anto, all your Thorns had OEM factory paint jobs. The 853 was Thorn's Red/Blue diagonal livery, probably in wet paint given the age of the bike.
Your later Thorns were powdercoated, spiffed-up by your carefully applied tape, stickers, and decals...I think I remember a blue shield for County Louth on the seat tube and World Championship "rainbow" stripes on the top tube, even some chrome tape bands originally supplied as handlebar finishing tape. All came out very nicely and tastefully.
That Releigh 753, though, as I recall Noel painted it for you. Wonderful red-into-white-into-blue fade. Probably acryllic 2-pack "wet" paint I know for sure it wasn't powdercoat.
Best, Dan.