this is from Jocelyn Howells booklet on plastics..BUFFED..these buttons are coated with or sprayed with paint,which is buffed from the high areas of a molded design to reveal the plastic color,which often is white or cream. Although many of these are celluloid,there are almost as many made of cellulose acetate. A hot-needle test will quickly confirm the typical camphor odor of celluloid-or no odor if acetate. These are the buttons sometimes referred to as "candy coated" or "French Celluloid"
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if you do a ebay search for buffed celluloid button you should see several listing...Peg