Vulcanite, Ebonite
Vulcanite is a combination of vulcanized rubber and sulfur, a material invented in 1843 by Thomas Hancock and used extensively in jewelry, combs, and buttons. It was particularly fashionable for mourning jewelry in the late Victorian era (1860-1900) after being popularized by Queen Victoria.
Gutta Percha
A hard rubber-based material that looks like wood, introduced in 1843. While still in production for use in dentistry, Gutta Percha hasn't been used for beads since the mid 20th century
Bois Durci
Made from a paste of fine sawdust and an organic binder such as egg white or blood, molded under high pressure and steam heat. Patented in Paris in 1855 by the Parisian writer Francois Lepage. Hard and highly polished, it was used as a wood substitute or to mimic jet, bone, or metal. Sometimes used to create religious medals that look very similar to bronze. (1)
Celluloid was introduced in 1862 as Parkesine, an artificial ivory. Popular into the first half of the 20th century. Beads were made of celluloid starting in about 1900 and were very popular during the Art Deco period. Celluloid is unstable and prone to significant changes with age; it may yellow with time, turn pinkish-brown, warp, or crumble. It's flammable and softens when exposed to mild heat.
Casein was first exhibited at the Paris Exposition of 1900 under the trade name Galalith. Under the name Erinoid, casein was exhibited at the first British Industries Fair in 1915, and an improved version was patented in 1950. Casein manufacturing continued until about 1980.
Casein plastic is made from chemically-hardened milk proteins, and does not melt into a liquid. Casein was usually manufactured in sheets and then mechanically stamped out in basic shapes, which were hand tooled into the finished objects. It can be dyed almost any color, or combination of colors, and often was used to imitate ivory, horn, or tortoise shell.
Casein can lose moisture over time, and sometimes you can see this as a subtle "crinkle" on the surface.
Bakelite, Catalin (Phenolics)
A heavy and dense plastic material. The first truly synthetic plastic.
As bakelite and catalin age, UV light causes a layer of phenyl alcohol to form on its surface. Phenyl alcohol is yellow-brown, so it imparts that tint to the original color. Thus cobalt becomes "blue moon" to olive green (see photo below), bright red becomes mahogany, white becomes butterscotch. Phenyl alcohol is an excellent sunscreen, so the discoloration only penetrates a millimeter or so. These plastics are very resistant to chemicals, and will never melt or ignite. Catalin, however, will shrink over time. This can result in warping and cracking of the piece.
Lucite, Acrylic
A common bead material from the 1930s onward. Early Lucite was not considered a cheap material, and can be found in rosaries with sterling crosses and centers.
Phosphorescent plastic dates from about 1960.