At the end of World War I, Kanae Yamamoto proposed an overhaul of the Japanese education system. He thought that it had been geared too much towards uncritical absorption of information by imitation and wanted to promote a less restraining system, a vision he expounded in his book Theory of self-expression which described the Jiyu-ga method, "learning without a teacher". Teachers Rinzo Satake and his brother-in-law Shuku Sasaki read Yamamoto's work and became fanatical supporters. They became keen to implement his ideas by replacing the many hours Japanese children had to spend drawing ideograms with black Indian ink with free drawing hours, filled with as much color as possible. For this, they decided to produce an improved wax crayon and in 1921 founded the Sakura Cray-Pas Company and began production. The new product wasn't completely satisfactory, pigment concentration was low and blending or impasto was impossible, so in 1924 they decided to develop a high viscosity crayon: the oil pastel. This used a mixture of mashed paraffin, stearic acid and coconut oil as a binder. Designed as a relatively cheap, easily applied, colorful medium, oil pastels granted younger artists and students a greater freedom of expression than the expensive chalk-like pastels normally associated with the fine arts. Until the addition of a stabiliser in 1927, oil pastels came in two types: winter pastels with additional oil to prevent hardening and summer pastels with little oil to avoid melting. State schools simply couldn't afford the medium and, suspicious of the very idea of "self-expression" in general, favoured the coloured pencil, a cheaper German invention then widely promoted in Europe as a means to instill work discipline in young children.