Prior to 1929, practically all of the underground cables in the Bell system were bare lead-covered cables installed in underground conduit of tile, wood or iron. About that time a new type of construction was introduced, in which the cables were buried in the ground without the use of conduit. Because bare cable thus installed might be subject to severe corrosion, it was necessary to develop suitable protective coatings.
The covering first employed on buried cables consisted of a flooding of asphalt over the lead sheath, followed by a wrapping of paper and a wrapping of jute, to serve as a cushion for two helical wrappings of steel tape. The tapes were then covered with additional jute servings to protect them against abrasion and corrosion. Asphalt was applied between the various layers and over the finished cable, which was also treated with calcimine, to prevent the cable turns from sticking...
