The articles below describes the early stage of the casein plastics industry (a little earlier than usually quoted). It was the second type of semi-synthetic plastic invented after celluloid, with the advantage of being less flammable and odourless!
The Age (Melbourne), 12th March 1897 page 3.
The casein protein was precipitated from milk by the addition of rennin. This early form of casein was not stable enough, however. It took the soaking of the material in formalin (5% solution of formaldehyde in water) to harden it sufficiently. This was a slow process, taking around one year for a 25mm sheet of the material. Once formed into sheets, rods, tubes or blanks, the plastic was usually machined into the required shape then polished and dyed.
As the plastic was made in various countries in the early 20th century it was produced under various names; Galalith, Syrolit, Erinoid, Lactoid, Dorcasine, artificial horn, Aladdinite, Karolith, Ameriod. An article from the Plastics Historical Society (see http://plastiquarian.com/?page_id=14228 ) claimed that in the 1920-30s casein was not as successful in America as in Europe due to competition there from phenolic plastics. None-the-less, casein buttons were produced there.
Galalith buttons were advertised in the Australian press from 1913, Eriniod from 1924, casein and Lactoid in 1930.
Casein buttons were popular as they were available in a wide range of colours, and took a beautiful polish. The material was easily surface dyed, allowing for fashionable colours and effects at short notice. Compared with other early plastics, it was resistant to washing, dry cleaning, and brief contact with hot irons. For these reasons, I suspect most early Australian buttons were made of casein plastic, especially those trumpeted as wash proof, dry-cleaning proof and iron proof.
Herrman & Co (predecessor of General Plastics) were making “Galalith” buttons as early as 1930, possibly earlier. “Herculoid” (artificial horn) button blanks were made as early as 1934 by G. N. Raymond in Melbourne. Eriniod Products were making buttons around 1936. G.Herring started making casein buttons by 1939. Cashall were also making casein button blanks from around 1940.
Casein buttons are still made today, but have largely been replaced by other plastics.
Apparently fat contained in casein makes the plastic opaque, which is probably why newspapers always stated that it was made from skim milk. Other things, such as the presence of buttermilk or riboflavin from the milk could spoil the transparency and colour. Alum added to the plastic mixture and the formaldehyde used to cure it both increased the opacity, as did poor washing of the casein, prolonged drying or increased temperatures! All the Beutron “Wash”, “Irridel” and Opal-glo buttons are opaque. There are no translucent or transparent buttons made by G.Herring until “Tecpearl”, made of polyester, were introduced in 1958.