Known as "yinzhang" () in China, "injang" in Korea, "inshō" in Japan, "ấn giám" (or "ấn chương") in Vietnam, seals have been used in East Asia as a form of written identification since the Qin dynasty (221 BC–). The seals of the Han dynasty were impressed in a soft clay, but from the Tang dynasty a red ink made from cinnabar was normally used. Even in modern times, seals, often known as "chops" in local colloquial English, are still commonly used instead of handwritten signatures to authenticate official documents or financial transactions. Both individuals and organizations have official seals, and they often have multiple seals in different sizes and styles for different situations. East Asian seals usually bear the names of the people or organizations represented, but they can also bear poems or personal mottoes. Sometimes both types of seals, or large seals that bear both names and mottoes, are used to authenticate official documents. Seals are so important in East Asia that foreigners who frequently conduct business there also commission the engraving of personal seals. East Asian seals are carved from a variety of hard materials, including wood, soapstone, sea glass and jade. East Asian seals are traditionally used with a red oil-based paste consisting of finely ground cinnabar, which contrasts with the black ink traditionally used for the ink brush. Red chemical inks are more commonly used in modern times for sealing documents. Seal engraving is considered a form of calligraphy in East Asia. Like ink-brush calligraphy, there are several styles of engraving. Some engraving styles emulate calligraphy styles, but many styles are so highly stylized that the characters represented on the seal are difficult for untrained readers to identify. Seal engravers are considered artists, and, in the past, several famous calligraphers also became famous as engravers. Some seals, carved by famous engravers, or owned by famous artists or political leaders, have become valuable as historical works of art. Because seals are commissioned by individuals and carved by artists, every seal is unique, and engravers often personalize the seals that they create. The materials of seals and the styles of the engraving are typically matched to the personalities of the owners. Seals can be traditional or modern, or conservative or expressive. Seals are sometimes carved with the owners' zodiac animals on the tops of the seals.