Casein plastics were introduced at the beginning of the 20th century, their starting material being the protein in cows milk, precipitated by the action of the enzyme rennin.
Although casein is readily moulded to shape under moderate heat and pressure, it does not produce a stable material for manufacture until it has become hardened by soaking in formalin (5% solution of formaldehyde in water) for a long period. Unfortunately, this causes much distortion so casein plastics are almost always produced by machining stock material such as sheet, rod, tube or buttton blanks (small discs). After machining, casein may be polished either mechanically with abrasives or chemically with a 'dip polish'.
The material readily takes a surface dye, so coloured items can be quickly made from pale coloured stock items. This was especially important for the button trade which was the principal consumer of casein plastics.
As well as buttons and buckles, casein was also used for knitting pins, fountain pen and propelling pencil barrels, dressing table ware and a host of other items.
In more detail
Casein, the protein in milk was used by the Ancient Egyptians as a fixative for pigments in wall paintings. It has also been used as a constituent in various glues but it appears not to have been used as the basis of a solid plastics material until the end of the 19th century. Krisch, head of a large firm of printers in Hanover experimented with casein to make a washable white board for replacing the slates used in school - paper was too expensive at that time for use by children to practise writing. He collaborated with Adolf Spitteler, a chemist in Bavaria and on July 15th 1899, a patent for "plastic compositions" was taken out in Germany.
The patent was taken up by firms in Germany (Vereinigten Gummivarenfabriken, at its factory in Harburg) and in France by Pellerin and Orosdi (Compagnie Francaise de la Galalithe, at Levallois Perret). The product was introduced under the trade name Galalith and was first shown at the Paris Universal Exhibition in 1900. A lot of development work was still required to produce a stable material, and the two companies merged in 1904 to form the International Galalith Gesellschaft Hoff and Company with a new factory in Harburg. A process starting with dried casein granules, known as the dry process, was developed and this was to become the universally adopted method for casein plastics manufacture and remained virtually unchanged throughout its history.
In Britain, a wet process starting with milk curds was patented in 1909 by a Russian student, Victor Schutze, from Riga. This material was called Syrolit and a factory of the same name was set up in a disused cloth mill at Stroud in Gloucestershire. However, it was not successful and by 1913 the company was bankrupt. A new company, was established at the same premises to manufacture casein using the dry process. The new product was called Erinoid and this was also adopted as the name of the company. Production commenced in 1914 and as supplies of Galalith were cut off at the commencement of World War I, the material found a ready market and button manufacturers from Birmingham were waiting on the doorstep for the first consignments. Lactoid, made by BX Plastics was introduced in 1922 at their Larkswood Factory in Higham Station Avenue, London. Young & Wolf Ltd. had a small production unit located at Bridgend Works, Stonehouse in Gloucestershire - they manufactured mainly rod, button blanks and knitting needles from about 1930.Young and Wolf pioneered the slicing of casein button blanks from rod in the UK.Charles Horner Ltd. of Halifax, England. like Young & Wolf, also produced casein plastics mainly in the form of knitting needles, button blanks and rod. Their brand name was Dorcasine.
These four British manufacturers formed the Casein Plastics Association (until 1938 it was called the Artificial Horn Manufacturers Association). At the commencement of World War II supplies of raw casein granules were no longer obtainable from Europe, the traditional source, and the CPA were encouraged by the British Government to seek alternative supplies in order to make buttons for military use. Argentina provided this need. In 1944, the CPA co-operated with The Knitting Pin Association and the Casein Button Manufacturers Association to form The Casein Plastics Joint Development Association, to represent the interests of both manufacturers and users of casein plastics. Perhaps the greatest contribution of the CPA was in the 1950s to improve the process for manufacturing casein granules. With the co-operation of the New Zealand and Norwegian dairies, this resulted in a casein of improved quality with a better base colour thus increasing the colour range, especially of very pale colours.
Erinoid remained the major producer of casein plastics in the UK until they stopped manufacture in about 1980. At that time they were part of British Petroleum. There were negotiations in hand for the sale of the casein business which was still profitable, but unfortunately these broke down. BX Plastics had already closed their Lactoid business in 1962 and all other British casein firms had also ceased production.
In the United States, casein plastics material was introduced by Christensen about 1919 and sold under the name Aladdinite. In 1924, Karolith was produced followed by Erinoid by a subsidiary of the British company. Casein did not achieve the same success in the US as it did in Europe - partly due to greater competition from cast phenolic resins, also some European applications were excluded because of the climatic conditions. Starting in about 1928 many casein manufacturing plants joined forces with button manufacturers to make casein directly into buttons. This included button manufacturer George Morrell who took over Kyloid, and Aladdinite who joined the Button Corporation of America. In 1931 Karolith Corporation, Erinoid Company of America, American Machine & Foundry Company and Pan plastics Corporation merged their casein interests to form the American Plastics Corporation to produce casein under the name Ameroid.
The first Russian factory for artificial horn was started up in1928 at Mnewniki, near Moscow.
Properties and Use
Casein has been described as "the most beautiful of plastics" and was produced in a wide variety of colours including delicate pastel shades, pearls and mottles, especially those imitating tortoiseshell and horn. The material also readily takes a surface dye and this process was extensively used to produce fashionable colours at short notice and for two colour effects by selectively cutting back the dyed surface layer. Casein plastics take an attractive polish which can be achieved mechanically with abrasives (except for surface-dyed material) or chemically by immersion in hot, hypochlorite solution - known as dip polish. Casein plastics are most frequently encountered in the form of buttons, buckles and knitting needles but it was also used for fountain pens, propelling pencils, dress ornaments, knife handles, necklaces, dressing table ware, manicure sets and a wide variety of items generally referred to as "fancy goods". It also found limited use for low voltage electrical plugs, sockets or jacks, mainly red or black, in the 1920s and 30s and sometimes as components of early telephones.
The manufacture of casein is a slow, batch process requiring the material finally to be hardened by immersion in formaldehyde solution - sections of about 25mm thickness requiring up to one year. Casein plastics are not readily moulded, although sheet can be pressed into a limited range of shapes, such as shallow bowls and candlestick bases, by 'hot stamping' . Instead, casein objects are fabricated from stock material such as sheet, rod or tube. Button blanks were stamped from sheet or sliced from rod but in the early years most were trepanned from sheet material.
As a button material it is resistant to washing, dry cleaning and can withstand momentary contact with a hot iron - unlike most other competitive early plastics materials, but with the advent of the newer plastics after 1945 its use gradually declined. However, limited quantities of casein plastics are still produced in some countries with large dairy interests, for example New Zealand, but specialised buttons are probably the only casein items manufactured today.