Seal is an important proof to win people's trust. There are two kinds of seals: the seals used by painters themselves and the seals collected by collectors. The painter himself sealed his works, which gradually became popular with the widespread use of famous works. After finishing the work, the painter should add a cymbal seal in addition to his signature to show that he made it himself. This situation began about five generations of Li. Mi Fei's History of Painting records that "Jinlian lay man", also known as a hermit, is a self-titled painting, which means Zhongshan lives in seclusion. Each self-painting must be titled tenor, printed with the seal of Inner Hall and the black seal of Jixian Academy. If there is such a seal, it will be written in the study. "

Because the seal has a strong texture, a seal can be used for several years or even a lifetime. Therefore, it is quite well-founded to distinguish authenticity with seals. However, because the seals are durable, they may still exist after the death of the painter, and future generations can use these seals to forge fakes. Therefore, the appraisal work can not only rely on the seal, but also be regarded as an auxiliary means. The seal of each era has the characteristics of each era. This feature can be distinguished from the shape, writing, engraving, texture and printing color of the seal.

In the paintings and calligraphy works of the Northern Song Dynasty, few painters and painters stamped their own seals on their works, and most painters and painters did not stamp their own seals on their works. In the Song Dynasty, most seals were made of copper and jade, and a few were made of other materials. There are two kinds of printing colors: honey printing and watermark printing (there are few mimeographs in the late Southern Song Dynasty). Honey seal is red and thick, and watermark is light and thin (mimeograph is clearer than honey seal and watermark because it is oily), but it is uneven in thickness when stamping on paintings and calligraphy. For example, in Song Dynasty, Hui Zong's calligraphy and painting seal "Imperial Book" printed a rectangular seal, which was different from that in Ming and Qing Dynasties. The printed color is red and thick, and it is a honey seal. The seals of "Escape from Zen" and "Yang Wuxia" in the volume of "Simitu" in the Song Dynasty are all light and thin, which are watermarks.

The seal characters and engraving methods of Yuan Dynasty seals changed, and a round Zhu Wen seal appeared. Most of the printing colors are mimeographed or watermarked, and the materials are ivory, jade, copper and wood. In the Yuan Dynasty's "Twilight of Autumn Mountain", the inscription is on this painting, and the border around the seal is very neat. The material of his seal must be ivory. Because the seal material and printing color are different, the effect of the cover is also different. After the Yuan Dynasty, painters not only signed and sealed paintings and calligraphy works, but also wrote inscriptions and suffixes, and the seals used also developed from one party to many parties at the same time.

Since Wang Mian began to carve with stones in Yuan Dynasty, more and more people have used stone carvings. At the beginning of the Ming Dynasty, the seals of various stones were quite common, and the methods of seal cutting characters also had new changes. The stop of each character in seal script is slightly thicker than the original stroke, commonly known as "hammerhead". There was no such seal script in Song and Yuan Dynasties, but it disappeared in the middle and late Ming Dynasty.

In the early Ming Dynasty, most painters and painters used mimeographs. Although they are red, they look pale and yellowish. Different from the printing color in Yuan Dynasty, the printing color used by the emperor, the highest feudal ruler in the early Ming Dynasty, was relatively red, which was different from that used by ordinary people. At this time, some painters and painters have more seals and different seal cutting methods. For example, Zhu and Shen Zhou painted the word "Qinan" at the beginning of the book "Sleeping", which is the same size, but not printed by the same party. Therefore, it is difficult to identify calligraphy and painting.

In the middle and late Ming Dynasty, Wen Peng was famous for printing, and was later called "Wen School". The literary school has developed the writing and engraving of seal cutting, and the handwriting is relatively clear, and some of them are engraved with marginal clauses, which is a new development and creation in the history of seal cutting. At this time, the seals were mostly made of stone, but precious materials such as crystal and agate also appeared. During this period, most of the printed colors were oil paints, and the colors were divided into shades. But some painters and painters use watermarks, which are uneven in color and fuzzy in nature. Although the mimeographed version has shades, the characters are clear.

In the late Ming and early Qing dynasties, the characters of seal script used by painters and calligraphers changed little, but the shapes and fonts of seal script tended to be diversified. Some painters' seals changed greatly in the early, middle and late stages, while others changed little, and their favorite seals were relatively fixed. For example, Yun's "The Book of Yun Zheng" has a white seal with a dent at the bottom, which has been stamped on several of his paintings in different periods.

In the middle and late Qing Dynasty, there were various specifications for seal cutting, such as Ding Jing's Zhejiang School and Deng's Deng School. Most of these factions take Shuo Wen Jie Zi as the main body, and many people carve it. And similar to Wen Peng's style, they carved the next paragraph on the side of the seal. At this time, stone is the first choice for carving. Most of the printing colors are oily, and the watermark is no longer used. There are also several blue seals, which are specially used for funerals.

In addition, there are some famous painters and calligraphers in the painting biography, and there are few works handed down from generation to generation; Or some unknown painters and painters, due to the small number of works, can not analyze and study the seal. At this time, we must first determine its time flavor according to various conditions, and then see if the time flavor of the seal is consistent with other aspects. If there are contradictions, we can study them in detail. If that work is the name of the Song Dynasty, but the seal is in the style of the Qing Dynasty, then we need to analyze it carefully: What about the seal of Zhong later? Or is painting and calligraphy itself fake?