The existence of evenly spaced parallel grain lines, especially in the faux-ivory jewelry pieces, are a giveway that it is celluloid.
It often yellows with age and so all those pale yellow/ecru-colored Deco era brooches seen today were much closer to either clear or white back then.
These generalized terms came into the language because at one time those manfacturers were the first and/or the most recognizable makers of a product.
And so it was with Celluloid, Bakelite and Lucite …
Celluloid is a semi-synthetic thermoplastic made from nitrocellulose and camphor.
It is safer to become familiar with the other characteristics of true celluloid than to risk deforming a piece by applying enough heat to generate any odor.
Characteristics: very lightweight; can have mold marks or not; can be solid, hollow or laminated.
Can be pretty much any color, including transparent or black (though sometimes black paint was applied).
Vintage jewelry made of (or with) plastic falls into one of six groups: celluloid, casein, cellulose acetate, phenolics which include Bakelite, and acrylics which include Lucite.
You’ll notice that I’ve only capitalized two of those names and there’s a reason for that.
Celluloid was widely used for a variety of items including jewellery, due to its versatility.