Oil paint can be diluted with an oil medium or solvents such as turpentine to be made into transparent
a. underpainting.
b. sfumato.
c. impasto.
d. glazes.

c. shubert i think : )

photography had emerged as an elite art pursued by a few creative individuals for a few wealthy patrons. but now, said bauldelaire, it was succumbing to "the great industrial madness of our times." it was becoming a mass production industry that catered to middle-class tastes, including a taste for gadgetry. the stereoscope, the first 3d imaging system, had turned looking at photographs into parlor entertainment. a "thousand hungry eyes were bending over the peepholes of the stereoscope as though they were the attic-windows of the infinite.