Embassy

According to Dictionary.com …

The Australian term ‘home brand’ relates to items packaged and marketed under the brand name of a particular retailer, usually a large supermarket chain, rather than that of the manufacturer. They are known as ‘own brands’ elsewhere.

Embassy was a home brand of G. J. Coles  from 1929, starting as a label for gramophone records and extending to cover many products until 1994.

Although these are the same style as Opal-Glo, Moonglow and Superglow buttons from the 1950s, they don’t appear to be made from casein which was not in common use by the 1970s, when these buttons were sold.