For Ruskin the process of decay began perhaps at the mid-point of Raphael 's career with his work in the Vatican ( Works, 12.148), or the point when Protestantism was separated from Roman Catholicism, since when Roman Catholicism 'had never shown itself capable of a single great conception'. ( Works, 9.58). At Works, 5.399 the process is completed with the death of Tintoretto in 1594. Certainly Ruskin counts the seventeenth and eighteenth painters such as Canaletto, Salvator Rosa, Claude, and Gaspard Poussin as painters with a high reputation who produced little of value. His depreciation of such painters was based on the assumption that the reputation of Italian painting had produced a lack of discrimination in responses to them.
Kugler, ed. Eastlake, Handbook of the History of Painting, Part One, The Italian Schools, First Edition, offers an academic perspective on the decline of Italian painting from a German perspective but published for an English readership.