Reference: Hartill 22.1290
16.5 grams; 33 mm; Fine Brass
1875-1887 AD
Reign title: Guang Xu, AD 1875-1908
ᠪᠣᠣ ᠴᡳᠣᠸᠠᠨ
Manchurian inscription "Bao Quan"
Board of Revenue Mint
Mother Coins 母錢 in old Chinese coin making
During the Han Dynasty, Chinese mints partially solved the inconsistencies in cast coins by using bronze master moulds. Master moulds were used to prepare the clay moulds which will be used for the actual casting.
Advances in the casting process in the sixth century resulted in the introduction mother coins (mu qian). Mother coins were used to impress the designs of the coin on very fine wet sand that would act as moulds for the coins. A mother coin was prepared by carefully engraving a pattern of the coin in a material that can be easily worked with such as tin.
The coin casting process involves the use of a rectangular frame filled with fine wet sand, presumably mixed with clay, and sprinkled with charcoal or coal dust. The dust allows the molten metal to flow smoothly. It also acts as a layer that separates the two halves of the moulds.
Mother coins are pressed on the wet sand in the wooden frame (first half of the mould). Rods are placed between the coins to create channels where the molten metal can flow. A second frame (second half of the mould) is placed on top and pressed tightly. This imprints the designs of the obverse and reverse of the mother coins on the sand in the frames.
The mother coins are then removed and transferred on top of the second frame to create new moulds. This processed is repeated until up to fifteen layers of moulds are created. The wooden frames are bound tautly and filled with molten metal, usually bronze.
This process creates a Coin tree cast coins connected by hardened metal on the channels. After brushing off the sand, coins are broken of the tree.
To make the edges smooth, the coins are strung together on a long square rod and the coin edges are filed down. It is further polished in tubs of chaff or sand before the final stringing.
The use of mother coins proved to be effective in controlling the quality of the coins. Slight differences between mother coins still existed however skillful the carver is.
