Later it was superseded with lead wrapped in paper, until the Knob and Tube system. This comprised of single-insulated copper conductors installed within walls and ceilings, this wiring was encased in porcelain insulating tubes with cloth-lined sleeves.
One knob for Live and one knob for Neutral. The wires were held in place by porcelain knobs nailed to the house frame. Where wires passed through wood framing, they were threaded through porcelain tubes to prevent them from contacting the wood.
https://down-ph.img.susercontent.com/file/sg-11134201-7repx-...
Remember that the first telephones were 1-wire with a ground return, and that configuration was quite common until the early 40's.
Small addendum: at least in Germany, early telephone wires (up until the 1950s?) were wrapped in paper, drenched in oil. The bundles were then enclosed in a lead-copper alloy to protect them from moisture.
https://commons.wikimedia.org/wiki/File:KabelbaumFMAachen_49...