I spent the two and one-half months between my meeting....

“ I spent the two and one-half months between my meeting with the Art Commission and the beginning of my actual mural work in soaking up impressions of the productive activities of the city. I studied industrial scenes by night as well as by day, making literally thousands of sketches of towering blast furnaces, serpentine conveyor belts, impressive scientific laboratories, busy assembling rooms; also of precision instruments, some of them massive yet delicate; and of the men who worked them all. I walked for miles through the immense workshops of the Ford, Chrysler, Edison, Michigan Alkali, and Parke-Davis plants. I was afire with enthusiasm. My childhood passion for mechanical toys had been transmuted to a delight in machinery for its own sake and for its meaning to man -- his self-fulfillment and liberation from drudgery and poverty. That is why now I placed the collective hero, man-and-machine, higher than the old traditional heroes of art and legend. I felt that in the society of the future as already, to some extent, that of the present, man-and-machine would be as important as air, water, and the light of the sun.This was the "philosophy," the state of mind in which I undertook my Detroit frescoes. ”

Diego Rivera

From : My Art