Seals came into general use in artistic work to identify the artist and to create a balance in the composition. One form of seal was referred to as a "balancing foot seal". Seals are used to embellish and enliven paintings, used like a spice to enhance and balance the painting.
Early name seals were usually small, about 2.5 cm square and 5 mm thick. Although the Imperial seals were very large requiring 2 men to make the impression. Originally the small seal's grip was pierced so a cord could be attached, later animal shapes were carved or cast as part of the seal's grip. As the seals grew in height, a grip was no longer needed but the grips continued to be carved in an assortment of shapes and animals such as, dragons, hares, lions, elephants, turtles, fish and figures. The grips on the seals became quite elaborate which made the seals themselves collected as works of art.
Seals are carved in two styles: Yang positive (relief) seals in which the characters are in red with white space around them. They are airy and lighter in mood, this is the male or groom form. The idea of Yang is said to include the concept of light, heat, day, south, positive, sun, heaven and spirit among others.
Negative (intaglio) seals are referred to as Yin. The Yin seal is more weighty and seems heavier. The idea of Yin includes shade, dark, water, black, lower, North, female force principle, moon earth and matter, among other things. Both styles are equally popular and many artists have name seals in both styles.
Seals come in several sizes and shapes, the shape and size will dictate the placement of the seal. Large, square and weighty seals are usually placed in the lower corner of the painting. Irregular, oval and rectangular shapes are placed on the sides. Name seals are usually square, whereas message or mood seals come in a variety of shapes sometimes fanciful to reflect or compliment the seals message.
Leisure seals (Xian Zhang meaning "not busy" - Japanese Yu-in or Ga-in), and the "lucky seals" (Ga Chi Yu Yin), are also referred to as mood or message seals and are the most interesting. These seals express thoughts, reflections, poetry and idioms. Artists not only collect these seals but also enjoy designing and carving new seals.