The Getty has released more books out to download for FREE! I have a couple of free ebooks, my favorite to date being, "Painting Landscapes in OIl Colour" (or a similar title) by Sir Alfred East.
There's a lot to be learned, and oftentimes there is something pleasingly soporific about the old writing style. If you want to blast through one of these old books and take notes etc., I recommend NOT reading them late at night:)
There are new books on old artists here as well. One on the watercolours of Cezanne looks interesting, one on Rubens and Bruegel...
Check it out below with the link. You're welcome