Straight Razors

A lot of the books on straight razors are well out of copyright. However, copyright does go back an absurdly long way and covers even the 1950s when they were still in relatively common use. The Internet Archive lends use of books based on how many they physically have in some warehousing arrangement and so you can borrow this one by the hour.

This seems like it was is in common use training barbers (and may still be -- there seems to be an edition still in print) and being towards the tail end of when straights were prevalent offers a different perspective from the older works.