This button is made of Bakelite, see below for technical details.
The colour of the back is known in button circles as apple juice bakelite.
The style of this button dates it to Art Deco in the 1920's and 1930's.

Phenol-formaldehyde Plastic, also known as PF, or Phenolic (Trade name: Bakelite), has been mass-produced since 1909.
It is a thermoset polycondensate.
The first volume-produced synthesized polymer resin, PF was used in early consumer electronic products such as telephones and radios.
A naturally brittle material in pure form, it is able to be strengthened with fillers such as wood pulp and cellulose.