Gasan (or 画賛 inscriptions associated with paintings) (画賛)
In China, a "gasan" is a text produced in relation to a portrait.
The term was mainly used up to the Tang dynasty. Text added to paintings in the Sung period and later was called 題 (dai) or 跋 (batsu). The term "gasan" began to be used more rarely.
賛 (San) is a style of literature which describes and praises somebody's performance.
In Japan, "gasan" refers to poetry written in a blank space, usually on the upper part of a painting. Sometimes it is written on a separate sheet of paper and attached to the painting. Many gasan are Chinese poems but Japanese tanka poetry or haiku (.a Japanese lyric verse form having three unrhymed lines of five, seven, and five syllables) are also sometimes written. A similar thing is 'shikishigata' (colored, square-shaped paper inscribed with verses, then cut and pasted onto the upper portion of large screens and sliding door panels).
An old example of san is written on the upper part of "Shingon Shichisozo" (figures of seven patriarchs in the Shingon sect of esoteric Buddhism) by Kukai (To-ji temple, Kyoto prefecture). The practice of a Zen monk giving his portrait (or called Chinzo) with gasan to his disciple after he had completed ascetic training was introduced together with the Zen sect after the Kamakura period. After that the practice of adding san to a painting became common. In the Muromachi period, many shigajiku (paintings with a san of Chinese poetry in the form of a hanging scroll) for which a san poem is essential were produced in large numbers, as were paintings by Zen monks such as Kanzan Jittoku or motif paintings with a san on their upper part (Kanzan and Jittoku were unworldly persons who lived in the Tang period and who were often used as the subject matter for paintings by Zen monks). Many paintings and ukiyoe woodblock prints from the Edo period have a san of kyoka (comic [satirical] tanka) or haiku.
A part (commonly an upper part) of a painting is marked with boundary lines to make the shape of a square, and in many cases this square is either painted in a different color to the rest of the painting or is whitewashed. An excerpt from Buddhist scriptures, poetry or inscription related to the painting is then written. It looks as if a shikishi (a square piece of paper often used to write a poem or to paint a picture on) was pasted on the painting. Shikishigata was already seen Wall painting in Dun-huang City of the Northern Wei period in China. In Japan, it was common in the Heian period. After the Muromachi period, shikishigata was used in paintings derived from Yamatoe group (a traditional Japanese style painting of the late Heian and Kamakura periods dealing with Japanese themes).