The Macchiaioli : Italian Painters of the Nineteenth Century, by Norma Broude
(A thorough study of this group of 19th-century Florentine painters, their working methods, influences, and the cultural-historical milieu that shaped them.)
Corot in Italy: Open-Air Painting and Classical Landscape Tradition, by Peter Galassi (Focuses on the period in which Corot traveled in Italy, painting his influential landscape studies. Traces the development of the tradition of artists traveling and painting in Italy.
Theory & Practice:
Painting Methods of the Impressionists, by Bernard Dunstan (any of Dunstan’s books are excellent)
Intelligent, scholarly discussions of working methods, materials, and practices of not only the major Impressionist masters like Monet, Sisley, and Pissarro, but also those of their contemporaries like Sickert, Whistler, & Sargent.
Landscape Painting: Essential Concepts and Techniques for Plein Air and Studio Practice, by Mitchell Albala
In a genre over-populated by recipes and formulaic dogma about landscape painting, this book is a refreshing alternative.
Little Journeys to the Homes of Eminent Artists: Vol. 1: Corot, by Elbert Hubbard, 1902.
Composition, by Arthur Wesley Dow, 1899
Notebooks, by Leonardo da Vinci
Alberti on Painting, by Leon Battista Alberti, 1435
L’Inferno, by Dante Aligheri, 1265-13212
Essays in the Study of Sienese Painters, by Bernard Berenson
ESSAYS, ARTICLES, EXCERPTS (on-line)
The Macchiaioli, by Norma Broude
The Artistic Training and Methods of the Macchiaioli, by Norma Broude
Words on Art, by Alan Feltus
Seeing, by Annie Dillard (from Pilgrim at Tinker Creek)
What Have We Made of the Landscape, by Rackstraw Downes
Why I’m a Painter of Landscapes, by Norman Turner
Addicted to Defeat: Reflections on Painting Outdoors, by Norman Turner
On The Art of Sketching Landscape, by William Gilpin, 1724-1804