Clark wrote and lectured during the decade. The annotated catalogue of the royal collection of Leonardo da Vinci's drawings, on which he had begun work in 1929, was published in 1935, to highly favourable reviews; eighty years later Oxford Art Online called it "a work of firm scholarship, the conclusions of which have stood the test of time". Another 1935 publication by Clark offended some in the avant-garde: an essay, published in "The Listener", "The Future of Painting", in which he rebuked surrealists on the one hand and abstract artists on the other for claiming to represent the future of art. He judged both as too elitist and too specialised – "the end of a period of self-consciousness, inbreeding and exhaustion". He maintained that good art must be accessible to everyone and must be rooted in the observable world. During the 1930s Clark was in demand as a lecturer, and he frequently used his research for his talks as the basis of his books. In 1936 he gave the Ryerson Lectures at Yale University; from these came his study of Leonardo, published three years later; it too, attracted much praise, at the time and subsequently.