"The light warm tint which Van Mander assumes to have been generally used in the oil-priming was sometimes omitted, as unfinished pictures prove. Under such circumstances, the picture may have been executed at once on the sized outline. In the works of Lucas van Leyden, and sometimes in those of Albert Duerer, the thin yet brilliant lights exhibit a still brighter ground underneath (p. 389).... It thus appears that the method proposed by the inventors of oil-painting, of preserving light within the colors, involved a certain order of processes. The principal conditions were: first, that the outline should be completed on the panel before the painting, properly so called, was begun. The object, in thus defining the forms, was to avoid alterations and repaintings, which might ultimately render the ground useless without supplying its place. Another condition was to avoid loading _the opaque_ colors. _This limitation was not essential with regard to the transparent colors, as such could hardly exclude the bright ground_ (p. 398).... The system of coloring adopted by the Van Eycks may have been influenced by the practice of glass-painting. They appear, in their first efforts at least, to have considered the white panel as representing light behind a colored and transparent medium, and aimed at giving brilliancy to their tints by allowing the white ground to shine through them. If those painters and their followers erred, it was in sometimes too literally carrying out this principle. _Their lights are always transparent_ (mere white excepted) and their shadows sometimes want depth. This is in accordance with the effect of glass-staining, in which transparency may cease with darkness, but never with light. The superior method of Rubens consisted in preserving transparency chiefly in his darks, and in contrasting their lucid depth with solid lights (p. 408).... Among the technical improvements on the older process may be especially mentioned the preservation of transparency in the darker masses, the lights being loaded as required. The system of exhibiting the bright ground through the shadows still involved an adherence to the original method of defining the composition at first; and the solid painting of the lights opened the door to that freedom of execution which the works of the early masters wanted." (p. 490.) * * *