Gypsum Interpretation Center 5/6
Mill house
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Mill house
Near the kilns there was an installation of which there are no remains and where the grinding took place, the aim of which was to break the stone until it was pulverised and then sieve it to eliminate the granules or waste. This operation, which was carried out without problems due to the low hardness of the product, required the use of various methods. Depending on the customs of each area, it was common to grind by hand, using wooden mallets called ‘palancas’ and ‘almádenas’ to crush the calcined stone. This was done by repeatedly striking the gypsum with the appropriate instruments.
In addition, grinding with a roller or “rueco”, in which a truncated cone-shaped limestone or basalt stone was dragged by a draught animal, horses, donkeys, mules or bulls on a threshing floor, was also common. To do this, the ground was cleaned, prepared and hardened, and the gypsum was spread out to form a heap, having been previously broken up with mallets and sticks to reduce its size, so that it could be rolled. Confirmation that the plaster was curled was obtained when a wave was formed when the roller passed over the ground material.
Grinding in a stone mill was also common and was carried out in the so-called blood mills, which were very similar to those used to grind other types of materials or products, such as oil. At first, their horizontal and vertical stones were moved by horse-drawn carriages and later by steam. In most cases, they were located in towns or near a road and the calcined gypsum was ground in different ovens, as was the case in the city of Valencia, where from the 16th century there is evidence of gypsum mills in the centre of the city, which were gypsum mills where the dehydrated stone was pulverised.
The mill was installed in a separate area like this one, to protect the process from inclement weather. The main difference with the oil mills is that the horizontal stone had a hole in the middle through which the gypsum fell onto a platform or sieve and then into a tank located on a lower level where it was stored until it was removed.
From the middle of the 20th century onwards, the vast majority of crushing mills were gradually replaced by hammer mills driven by chain motors, crushing machines or diesel or electric crushers, and therefore water tanks were often built to cool these motors.
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