One of the distinctive characteristics of Chinese painting is the use of inscriptions in poetry of calligraphy and of special seals as part of the painting itself.  This was a major contribution made by scholar painters.  Its significance lies in its ability to express the theme and artistic conception of the painting more clearly and deeply while, at the same time, giving great insight into the artist's individuality, emotions and views on art and life.   In ink-and-wash paintings, the bright red seal adds a final touch of beauty.  When preparing the inscription and seal, therefore, the Chinese painter, in addition to considering their content, has always given great thought to the placement, length and dimensions of the inscription and the position of the seal on the painting.

The simplest inscription consists of the artist's name and the date.  Sometimes the inscription could include the occasion for the painting and the name of the person for whom the painting was done.  It could be about the subject and style of the painting. Quite often the artist might include a piece of poetry or a literary allusion.

These are all followed by the artist's own seal. Xu uses the stamp Kongu which is an artist's "nickname" or "philosophy" which roughly translates to an image of a clear open valley, "there is nothing there but there is also everything there". This comes from her relationship with the concepts of Zen.

In the Shang Dynasty, seals started being used in the government offices, where they represented authority and power. During the Shang and Zhou Dynasties, the material for seal making was mainly animal bones, copper (bronze) and pottery, and there were specially trained, sophisticated artisans or craftsmen, including potters majored in this work - making seals. Because seals in this period were mainly used in governments and mainly by nobles and officials, the style of seals should be very formal and beautiful. In the Shang Dynasty, the oracle bone script (Chin: 甲骨文) was used, and during the Zhou Period, various scripts (because the Chinese characters were still not unified then) but mainly Dazhuan (chin: 大篆) or Jinwen (Chin: 金文) were used.

In the Qin Dynasty, the more regular and formal seal script called Xiaozhuan (Chin: 小篆) was formalized by the Chancellor Li Si and was announced by the Emperor Qinshihuang, thus the written script of Chinese characters was unified for the first time. Due to the development of Chinese architecture, seals of this period were also widely used in building materials, e.g. after finishing a tile or a brick, the maker normally stamped his seal on the surface. This can be seen on the antiques of this period. Such seals, beside indicating the producers' names, time or place, already have various styles, reflecting the personal characteristics of the manufacturers.

In the Song Dynasty, scholar-artists flourished, and seal making became popular. Since this era, soap stones have been widely used in seal cutting. Stones from Qingtian, currently Zhejiang Province, are named Qingtian Seal-stone (Chin: 青田印石); and the soap stones named Shoushan Seal-stone (Chin: 壽山印石) from Fujian were also widely used. Some artisans became experts, creating numerous carving styles. Also during this period, seals started being used as signature for paintings and works of calligraphy.

In the Yuan Dynasty, seal cutting was already a very developed art. The Ming Dynasty and Qing Dynasty were two golden periods for the art of seal cutting. In the Qing Dynasty, soap stones from Mongolia named Balin seal-stone (Chin: 巴林印石) began to be used. Nowadays, a work of Chinese painting or calligraphy normally has its seal(s).

The seals can be carved in stone (usually soap stone).  It can contain a name, poetical saying, a design or symbol which has a connection with the painting.  The seals are pressed into a pot or tin of cinnebar paste, a scarlet red color, and are impressed onto the painting.  The paste contains mercuric oxide, ground silk and oils. It required a careful stamp as it is rather permanent.  When using red seal on a monochrome painting, it is said to be "adding the eye to the dragon".