We were watching Antique's Roadshow (as one does), when a copy of "Text Book of the Madam C.J. Walker Schools of Beauty Culture" (1928) came on.
They showed this image in the book, which caught my eye: "Bobbed Hair Types"
The story of Madame C.J. Walker is fascinating. Born Sarah Breedlove, Madame Walker was known as the first female self-made millionaire in America. She developed many beauty products for African-American women and trained "beauty culturists." She is often miscredited with the invention of the hot comb, which was used earlier in France in the 1800s, however she received a patent for a version with widened teeth.
Further reading by Henry Louis Gates.
(Totally random side note: I met him on a plane once and he was one of the nicest and most interesting people.)