Reddit mentions of Magical Secrets About Thinking Creatively: The Art of Etching and the Truth of Life

In my opinion (and I hold an MA in printmaking, with years of focusing on etching exclusively), Crown Point Press is the authority for all things etching-related; and they've published several incredible volumes detailing the techniques they use in their studio, the "Magical Secrets" series. Here's the one on line etching & engraving. The others are on general etching, aquatint, and chine colle. I personally own the aquatint and chin colle ones, and really can't recommend them highly enough.

Printmaking: History and Process is another title that comes to mind, and a book I think every shop should have a copy of. It's from the 70s and so won't cover any of the digital hybrid techniques that have become so popular over the last few decades... but for a detailed overview of those parts our craft which haven't changed much in centuries, I know no better reference. It's been out of print for some time now, so you'll probably only be able to find used copies—but good news is, it looks like the prices on those have come down some. I paid $40 for a used copy a few years back and thought that was a steal at the time.
Good luck!