Hello - These are most likely made of celluloid. They were used for many things - as silverstatetreasureboxes pointed out they were affixed to vanity items - trinket box covers, mirrors, etc. They were also affixed to the center of black bakelite pendants and pins - if you search -celluloid bakelite cameo - you will pull up pendants and pins with ivory-colored celluloid pieces just like yours glued onto them. They can be found in late Victorian mourning pieces, c.1905, up to the 1930s. Your pieces look as though they are from the 1920s.
