Calamine process

Figure 6.2 Uptake of zinc during the calamine process as a function of temperature. (Adapted from Haedecke, 1973 Figure 6.5, with permission.)...

Another reference, this time probably to the calamine process, appears in the works referred to as a pseudo-Aristotelian compilation called On Marvellous Things Heard , probably written in the 3rd Century BC. As translated by Caley (1967 67), the relevant passage runs ... 

If we accept a date of around AD 1000 for the commencement of the distillation of zinc on a large scale, then, following the work of Craddock (1978), all earlier brasses should contain less than 28% Zn, as this is the approximate upper limit for the calamine process at around 1000 °C. Above this temperature, the process is more efficient, but it is said that the brass produced melts and the active surface area for the process is thus reduced. By granulating the copper and therefore increasing the surface area, the maximum can be pushed to around 33% Zn, but it is unlikely that this was done in Europe until the 18th Century (see Section 6.4). This model is supported by the analytical data Craddock s work on Roman brass indeed shows an upper limit of about 28% zinc. 

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