The earliest wiring methods I've seen here were: individual cloth and rubber covered wires in isolators (glass or porcelaine), twisted lamp cord style wire on isolators.
Later on they used tar impregnated cloth wire, either in Bergmann conduit (basically asphalted cardboard with a thin metal sheathing around) or just in plaster. That wiring method was used until the advent of PVC insulated wires in the 1950ies. Bergmann conduit survived until around 1960.
Some months ago I found a place where somebody had tried to "replicate" the old wiring... by twisting blue PVC-isolated conduit wire and stringing it up on a few nails down in the moist basement... good thing the house was scheduled for demolition just a few days later... (but just for the dodgy wiring, otherwise it was a real shame for the old rock-solid 1900 brick house!!!)
