DDS (Det Danske Sukkerfabrik - "The Danish Sugarfactory") -- multistage process involving pre-liming where the pH of the juice is gradually increased to start precipitation of proteins, followed by addition of further lime and gas.
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Dorr (also Dorr-Oliver) - a continuous process using two tanks with recycling ("1st carbonatation") to build up particle size for natural flocculation.
A reason for the lightness of the rocks was apparently due to blood soaking into the stones when they were used as missiles during battles; however, nowadays chemical weathering - carbonation - of the limestone is thought to account for their light mass.