By 1915, European manufacturers of casein had found a viable method of making high-quality casein plastic. Dry casein could be slightly moistened with water, and then processed into a plastic by applying pressure and shear, as in a heated extruder.
It was not until 1919 that the first casein plastic that was up to European quality standards was made in the U.S.
5) remained among the main products in which casein could be used, pending a method of reducing the absorption of water from humid air) But casein plastic still required hardening in formaldehyde, making its manufacture a long and costly process.