Collectors of vintage plastics, whether buttons or other items, are curious and/or puzzled as to what plastic materials are in their collections. Unfortunately, without destructive testing such as hot needle testing, burn testing or specialised testing such as spectrometry, it can be hard to tell. Unfortunately, some plastics are excellent for mimicking both non-plastics and other plastic materials.
Recently I have described a couple of the plastics used in Australia; casein ( http://www.austbuttonhistory.com/?p=12876 ) and Lucite ( http://www.austbuttonhistory.com/?p=12748 ).
The 1958 Tariff Report into buttons stated that, as of 1957, General Plastics were making buttons from casein, acrylics (a.k.a. Lucite), polyester and metal. Bijou mainly produced casein and acrylic buttons. G. Herring were making casein and polyester buttons.Therefore, if you have Australian plastic buttons they are likely to be made of casein, acrylic or polyester. The manufacture of casein buttons was increasingly replaced by synthetic from the late 1950s.
Polystyrene may have been used, but before 1954 it had been abandoned for use by Australian button manufacturers as it melted upon drycleaning. Some Beauclaire cards from the early 1950s mention that phenol (a.k.a. Bakelite or Catalin) and urea (a.k.a. Beetle, Amino or Plaskon) were used in their buttons of the time.
In 1954 an advertisement mentioned that cellulose acetate was produced in Australia for General Plastics.