I have a Great Eastern 73 with handles of this material. I have't had any problems like those associated with celluloid as of yet. It is apparently an early plastic derived from milk proteins. Here's what Wikipedia says:
Galalith (Erinoid in the United Kingdom), derived from the Greek words gala (milk) and lithos (stone), is a trade name for one of the earliest plastics.
It was invented in 1897 and patented in 1899 by (Friedrich) Adolph Spitteler (1846 - 1940) and Wilhelm Krische and made from the milk protein
casein. At the beginning of the 20th century, a French chemist, J.C. Trillat, discovered the means to insolubilize
casein by immersion in formaldehyde.
This material revolutionized the button industry with its capacity to create structural effects and imitate all sorts of material: horn, tortoiseshell, ivory, wood, etc. It was also used in the 1930s for jewellery, pens, umbrella handles, white piano keys (replacing natural ivory), etc. World production at that time reached 10,000 tons.
One of its great qualities is its porosity, making it ideal for dyeing, by immersing white galalith in coloured baths. Galalith cannot be moulded, and is manufactured in the form of sheets of different thickness, sticks and tubes, and is therefore worked by hand.
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http://en.wikipedia.org/wiki/Galalith"
Hope this helps!