Mould line (parting line), line or area-like elevation (flashing) on cast goods, resulting from the penetration of the cast material into the joints of the mould. As a rule, mould lines are removed; only in the case of art casting is the mould line often left in place so that the perfect reproduction of the object can be recognized. The image above shows flashing along the mould line of the sprue and a tiny mould line along the right leg of a 40 mm Prussian guard grenadier officer cast in a Creartec mould.
Mould lines on miniatures need to be removed prior to painting. These 40 mm Zinnbrigade fusiliers of the Anhalt Infanterie-Regiment are a case in point how priming and painting tends to accentuate the mould line such that an otherwise acceptable paint-job is ruined. In retrospect, it was a mistake not to invest a few extra minutes to completely remove the mould lines from these figures. See Removing Mould Lines for details.
The fusilier on the right exhibits an even more serious casting problem, called mould offset, which is virtually impossible to repair. The mould halves were misaligned during the casting process, resulting in a distorted mould line which happens to run right through the figure’s face. This casting should have never made it to the painting queue, but gone right back to the melting pot.
Source: Meyers Großes Konversations-Lexikon, 6. Auflage 1905–1909