Here are more examples, this time from Floor.

The phenolic bead is about 34 mm diameter. The single natural amber bead is a nice "egg yolk" color. The three amber disks are from Idar-Oberstein and represent "pressed" amber - amber that has been heated under pressure. The "sun spangle" inclusions and clarity are indications of pressure treatment.

Three square-ish beads were found by Floor on a necklace sourced in India and are really good imitations of pressure-treated amber, but these are thermoplastic - either Lucite (poly (methyl methacrylate) also called acrylic) or polystyrene. I'm still working on a quick & dirty method to ID some of these thermoplastics.

Finally, there were three mystery beads. These appear to be some kind of thermoplastic but emit a very strong perfume-y odor when reamed or needled. The scent reminds me a bit of sandalwood or maybe myrrh, but not exactly. Update - I believe these beads are celluloid - the scent is actually camphor.

Thanks Floor and John for saving these examples for me to study!