The Yan state was the originator of the knife coin, basing their currency off of the tool commonly used by the populace. The knife was an important and widely-used tool, so the shape had familiarity and value. The Chinese place much value on objects and ideas important to the function and prosperity of society, so the early currencies were based off of tools that contributed to the prosperity of China: knives and spades. It is estimated that knife currency was introduced around 600 BC, though it could be earlier or later. The State of Yan produced these knife coins until it fell to the Qin state in 222 BC. (Image from https://en.m.wikipedia.org/wiki/Yan_(state)) The earliest knife coins had broad, rimless blades that came to a pointed tip (so they are fittingly called pointed-tip knives). The “cutting edge” of the blade is unobstructed as on actual knives. The back of the blade has a relatively tall ridge, which represents the reinforcing structure seen on actual knives. These are the closest representations of actual knives. (Knives 1 and 2 from the left fall into this category) The knives bagan to have a more-stylized shape with the top edge being curved. However, the above attributes are still present. (Knife 3 from the left falls into this category) Then the knives were given a rim around the circumference of the blade, possibly to deter clipping. This began the trend of making the knife coins less and less like actual knives. (Knives 4 and 5 are in this category). Until now, the obverse inscriptions all featured numbers or cyclical characters. Sometime around 400 BC, the state of Yan began inscribing all of their knives with the same character on the obverse and additional characters on the reverse. This character has traditionally been said to be “Ming”, or “moon”, but it is a bit more likely that this character is “Yi”, the capital of Yan and a major mint for these knives (I will still call the “Ming” knives though for colloquial ressons). Knife 7 still retains a slight curve on the top edge, while knife 6 has a flat top edge. I am not sure what the correct order for these two knives is (knife 6 has a style closer to the pointed knives, while 7 still has the curved top edge). However, they are both very early “Ming” knives. Soon the rims became very thick around the blade. This would set the style for all future Yan knives. Knife 8 is one of the earliest knives to have this style of rim. The obverse character still retains the shape of the earlier 6 and 7 knives. The obverse character become more compact and the reverse inscription became more complex. The rims became a little more defined. The back edge of the knife still retained the gentle curve seen on all of the earlier knives. Finally, the obverse character became even more compact, and the back edge of the blade and handle were each straight, and met at a distinct angle. This is by far the most common type of knife coin produced, and it is available for fairly cheap ($30-50 in nice condition). They have been found across a large area, including Korea and Japan, showing how they were a staple of the ancient Chinese trade economy. Another knife coin found in Yan territory is a rare variant called the “needle-tip” knife coin. The purpose of these is unknown. I believe they are a local variant because they do not fit in with the progression above. Some believe that they are the original knife coins and were quickly abandoned due to impracticality, but the blades have a rim around the perimeter, making this theory highly improbable. They have roughly the same fabric as knives 4 and 5. Next steps of course would be to assign dates to each type to narrow down the time range from 200 years for each type to 50 or less. There is a clear evolution, and it seems silly to lump all varieties into the same group and date range. But that will take archaeological hoard evidence which I do not have access to at the moment. Maybe later. I hope this was enlightening and fun to read, and feel free to post anything relevant!