Great Seal script (大篆, daiten) in the broad sense of its definition includes oracle bone script (甲骨文, koukotsubun) and kinbun (金文, literally, “text on metal”, and more precisely bronze). Great seal script was further unified in 221 B.C. under the name of small seal script (小篆, shouten).
Kinbun existed simultaneously with oracle bone script. In fact many styles were in simultaneous use, sometimes for hundreds of years or more. We still use seal script today for carving calligrapher seals, although, not only for that purpose. Corporations in kanji using countries have official stamps made in seal script, too.
The origins of kinbun may extend back as far as the beginning of the Bronze Age in China, or the Xia dynasty (夏朝, 2070 - 1600 B.C.). At that time, oracle bone script was used for more practical purposes such as divination and recording historical events, where kinbun was playing more of a decorative role, being carved or cast on bronze tripods, cauldrons, bells and other vessels.
The interesting thing is that even though oracle bone script was the first systematic writing script in China, it is important to point out that recent findings prove that pictographic words directly related to later forms of kinbun appeared as early as the 16th century B.C, thus preceding koukotsubun.
Kinbun of the early Shang dynasty (商朝, 1600 - 1046 B.C) was used to identify the owner of the inscribed artifact, and also to express power and status of the ruler through these artifacts. One needs to keep in mind that bronze was the most precious metal at that time. Gradually, engraved bronze-ware was also used for religious purposes, for tributes of recognition from one clan paid to another, memorials honoring the deceased, etc. Those inscriptions delivered an astonishing amount of information about ancient history, as well as the development of calligraphic art.
Kinbun of Shang dynasty was extremely decorative in a way, yet simple and well designed. The variety of line thickness, the smooth curves, character size differences, and their virtually infinite forms make kinbun a real treat for both the eye and the soul.
The irregularities within the script seem to dissipate towards the Zhou dynasty (周朝, 1046–256 BC). Some zoomorphic patterns were simplified and become more abstract. During Western Zhou (西周, 1046 - 771 B.C.) when ancient calligraphy reached the first peak of its development, kinbun was showing the first signs of transformation into small seal script which had more standardized character forms.