|Number of mentions published in books|
via N-Gram viewer—Velazquez in blue)
|Diego Velázquez, Pope Innocent X, 1650|
Velázquez held a respected position among many academic painters, especially Carolus-Duran, who encouraged his students to travel to Spain to see the originals and to make copies from them.
The reverence for the Spanish master was so great that a "cult of Velázquez" emerged in 19th century Paris, where some artists mystically appealed to his ghost to guide their hand.
The key to Velázquez, Carolus-Duran said, was strict simplicity of tone and careful attention to half tones, the planes that transition the form from light into shadow.
A book from the period called "The Art of Velázquez" by R.A.M. Stevenson, student of Carolus-Duran, can be downloaded for free at Archive.org.