I've been buying lots of vintage bangle bracelets lately to sell in my Etsy shop and wanted to find out more about what they are made of. They are plastic, but many Etsy shops have similar ones listed as Lucite.
So, I asked a veteran plastic seller on Etsy, Age Of Plastic https://www.etsy.com/shop/AgeofPlastic, for some advice. Here is her response:
Lucite can be molded or carved. It can also have seams, although I don't
know how common that is (I think I've owned one Lucite bangle with a
seam). On your better Lucite pieces, even if they were molded, they will
have been polished to remove any sign of mold marks.
Generally speaking, collectors and sellers consider the presence/absence
of mold marks and seams to be an indicator of quality, and occasionally
to exclude a plastic when identifying. In some types of pieces, like
Japanese celluloid floral bangles, seams are expected because of how
they were constructed and have no bearing on their value.