2nd and 3rd series: Bakelite and thermosets.
In the first half of the 20th century, the term Bakelite had become virtually synonymous with plastics, and since the emergence of its thermoplastic descendants, the vernacular has used the name to distinguish the old, heavy thermosets (melamines, phenolic resins) from what it more or less disparagingly calls just "plastics". Bakelite, however, is not a generic name, but a brand name, contrary to what everyone assumes on the basis of common usage, namely one of the Bakelite AG in Iserlohn (which, since its parent Rütgerwerke sold it to Borden Chemical in 2005, has enjoyed alternating motherships by American chemical companies and is now owned by Momentive Specialty Chemicals). This leads to a terminological problem: Bakelite is a thermoset, but not every thermoset is Bakelite. So we have to distinguish: The black and white switch series are both molded from thermosets, but only the black series is Bakelite in the trademark sense, while the white series is molded from a related resin. You can read more about Bakelite and its significance in material and cultural history as well as about its career as a cult material here.