Green ink is an oily smoke ink, which is made of tung oil and other oils by burning smoke. It is characterized by fine smoke, good luster, black color, uniform ink body and smooth and silent writing. In addition to the characteristics of ordinary oily cigarette ink, green ink is black and bright in color and has a faint fragrance. It integrates painting, calligraphy and printing, and is the best in Four Treasures of the Study.