Because writers, as I’ve observed before, are intellectual packrats who gather up odd bits of information just in case they may need one of them someday: The scholarly hairdresser who figured out how to do the Vestal Virgins’ seven-braid hairdo also takes on 18th-19th century papillote curls — the “curling-papers” we read about in period fiction.
When I googled on “papillote curls” to retrieve the link, I also found links to blogs where other recreationists have gone on to try the process themselves, which is how I learned that the process works best on hair that hasn’t been washed for a day or so — “every day” hair-washing being a mostly 20th-century innovation. And in the “everything is connected to everything else” department, I liked the hairdresser’s comment that this particular style and curling method didn’t become popular until technology had advanced enough for paper to become relatively cheap.
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