The 1950s and 1960s versions of both ‘Opal-Glo’ and “All Purpose” buttons shows that the same plastic appears to have been used. G. Herring (later Beutron Australia) claimed that Opal-Glo buttons were made from “two American formulae”; however, they are made from casein plastic.
Interestingly, casein buttons were not as popular or common in the States, although indeed made there, as Bakelite/Catalin buttons were preferred. Casein buttons are still made, but the plastic is more expensive than alternatives preferred today, such as polyester.
Not surprisingly for a brand that lasted decades, the graphics used changed several times.
These are all “fish-eye” sew-through buttons. I don’t think they look like fish eyes; perhaps like cats eyes. That is, apparently, an alternate name for them.
This style was already so established in the mid 19th century that it needed no explanation, often referring to pearl shirt or blouse buttons.