Rudolf Steiner recorded his view of the world in numerous books. He also gave more than 5,000 lectures, in which he explained his ideas, using only minimal notes. When describing especially difficult subjects, Steiner frequently resorted to illustrating what he was saying with colored chalk on a large blackboard. After his earlier lectures, the drawings were erased and irretrievably lost. After the autumn of 1919, however, thick black paper was used to cover the blackboards so that the drawings could be rolled up and saved. The Trustees of Rudolf Steiner's Estate in Dornach, Switzerland, possess more than a thousand such drawings. A selection of these drawings was first shown to the general public in 1992, and since then, exhibitions in Europe, America, and Japan have generated much interest in Steiner's works.