Ted Puls writes:

From the beginning of the Silk Road, the Chinese cast Wu Zhu coins as the primary money for most of the people on earth. The "militant" Emperor Wu of the Han Dynasty changedthe previous long-lived coinage called the Pan Liang ("half ounce") into his coinage called the Wu Zhu ("five grains") in 118 B.C. This coinage was to be the preferred money untilthe founding of the Tang dynasty ca. 600 A.D. These coins circulate much longer. Some were recently found in a Liao Dynasty site dated 400 years later. The British found themcirculating during the last imperial dynasty in the 19th century. They were copied for trade along the Silk Road using metals available to local mints. These were sometimes closeto the originals and sometimes were made in distinctive types with a mix of the Chinese writing and the local Kotan writing on the same coin. The Official coinage was often verynicely cast but also degraded when the economy required debasement.

During the later times called the Eastern Han the quality dropped significantly with the power of the emperor. After the fall of the dynasty a remarkable coinage of Wu Zhu werecast in amazingly small and light weight sizes by the temporarily successful general who defeated the Han. After this time of trial, a myriad of dynasties and kingdoms came andwent often reviving the coinage somewhat. Wu Zhu were cast for at least 400 more years during these turbulent times.

During the late Han Dynasty, the various mints began the curious practice of using varied marks in addition to the wu and zhu characters on the coinage. These marks weresometimes placed in the mold to result in a raised character and the marks were sometimes engraved into the surface after casting. The purpose of these marks is unknown at thiswriting. This unknown is one attraction of collecting these mysterious artifacts. I have not seen a satisfactory way of organizing these myriad marks to allow a start toclassifying and of understanding them so this is my attempt. The number of marks or symbols is limited but the many ways they were used and combined in a vast quantity of typesthat calls for a system of organizing them.

The most common mark is a plain dot. These Chinese minters were able to derive many varieties out of this simple mark. To begin I suspect that the mint organized marksusing a traditional ideal of the farm layout using the 9-field system to divide land in a community in a pattern like a tic-tac-toe game. The center square field is the coin'ssquare hole. Above and below this central hole are two common areas to place marks. Dots were arranged in 3 fields above and below the field containing the wu and zhu charactersand in the field containing the characters. Dots were also placed on the reverse of the coins.

This simple start is made more complicated by additional options in dot placement. The "dot above the hole" varieties seem to have dots placed near the inner hole, in themiddle of the field, and also need the outer edge (low, medium and high placement). The dot on the hole was sometimes a half dot. If this wasn't enough the dot also could beplaced not only centrally, but also to the right and the left of the middle of this "field". The total number of possible dot positions above the hole is nine. Below the hole thesame numbers of possible spots can be seen. Spots for dots also were displayed in the fields above and below the wu and zhu characters. Zhu will have a similar set of options fordot placements.

I haven't discerned the vertical low medium and high positioned dots in these fields. This suggests that three positions for dots exist in the fields above each character butalso three more each for fields below these two characters. The wu containing field on the right of the hole has its own set of dot placements. Wu can have a dot in the middle ofthe character where the lines cross. Inside the hourglass like figure of wu, regular dots were placed in the upper space, the lower space, and sometimes a dot was placed in theupper and lower space. Triangular dots are found inside the hour glass also, which seem to be a distinctive design. Less commonly dots were places beside the waist of the Wucharacter toward the inner rim or on the outer rim side. Zhu dots are less clear. Some feel that raised area on the character are intentional dots rather than casting flaws. Ihaven't seen these dots repeated on two coins and believe they are casting errors.