In article ,
Harry Bloomfield writes:

1950's though would probably be VIR - rubber insulation which becomes
very brittle covered by a waxed woven cotton for protection, or rubber
with a tough rubber overlay for protection. So the VIR would look a
red/brown colour, rather than red - all well overdue for replacement.

PVC was in use by 1955, but not exclusively so -- rubber was
still being used too. There may be no earth in 1950's lighting
circuits -- it was optional. If there is no earth, you can only
use class II (double insulated) light fittings.

--
Andrew Gabriel