imprint taken from calligraphy engraved on stone or wood. The practice emerged in the Tang dynasty (618–907) as a method of studying the style of earlier calligraphers and developed into an important related art form in itself. The rubbings served as models for copying and training. Calligraphers during the Song dynasty (960–1279) became especially interested in the aesthetic principles guiding brushstroke and composition and their application as criteria for judging calligraphy's sister art, painting.