Mother coin
In the manufacturing process mother coins were used to impress the design in moulds which were made from easily worked metals such as tin and these moulds were then placed in a rectangular frame made from pear wood filled with fine wet sand, possibly mixed with clay, and enhanced with either charcoal or coal dust to allow for the molten metal to smoothly flow through, this frame would act as a layer that separates the two parts of the coin moulds.
[7] Before modern industrial patterns were introduced into almost all fields of production, coin mints can be considered to be an outstanding example of an early form of mass production of attempting to create identical objects, or those as standardised and as similar to each other as possible.
[1] Therefore, it wasn't only just the technological knowledge and the techniques that were applied which mattered, but also the general organisation and especially the division of labour that were crucially regarded of being of paramount importance to the assessment of both the efficiency and quality of the work of coin mints.
[1] It wasn't until the Song dynasty period that contemporary sources started to actively record the works of coin mints to give insights into these early instances of mass production.
[1] During the Northern Song dynasty period a scarce number of sources started providing written evidence for both the usage of the "sand casting method" (翻砂法) and the application of mother coins to this process.
[1] Notably, the Rhapsody of the Great Smelting records the sentence "scrubbing the cash coins with grain chaff", which wouldn't be mentioned again in the historical records 689 years later in the Qing dynasty period 1899 book A Survey of Casting Coins (鑄錢述略), which indicated the long continued usage of this method.
The introduction of ancestor coins under the Manchu Qing dynasty lead to all mints having more consistently produced coinages and smaller variations between the coins produced by separate mints in both inscription (or legend) as well as in quality.
