El Greco (1541-1614) painted many of his paintings on fine canvas and employed a viscous oil medium.
He painted with the usual pigments of his period such as azurite, lead-tin-yellow, vermilion, madder lake, ochres and red lead, but he seldom used the expensive natural ultramarine.
Scholars' conclusions about El Greco's aesthetics are mainly based on the notes El Greco inscribed in the margins of two books in his library.
El Greco discarded classicist criteria such as measure and proportion.
He believed that grace is the supreme quest of art. But the painter achieves grace only if he manages to solve the most complex problems with obvious ease.
El Greco regarded color as the most important and the most ungovernable element of painting - "I hold the imitation of color to be the greatest difficulty of art" - Notes of the painter in one of his commentaries).
He declared that color had primacy over drawing; thus his opinion on Michelangelo was that "he was a good man, but he did not know how to paint".
Francisco Pacheco, a painter and theoretician who visited El Greco in 1611, was startled by the painter's technique:
"If I say that Domenico Greco sets his hand to his canvases many and many times over, that he worked upon them again and again, but to leave the colors crude and unblent in great blots as a boastful display of his dexterity?"
Pacheco asserts that "El Greco believed in constant repainting and retouching in order to make the broad masses tell flat as in nature".