In medieval India, the process of indigo extraction underwent great improvement as a result of the:

  1. A. use of fertiliser enhancing the quality of indigo crop.
  2. B. introduction of mechanical crushing tools for indigo stems.
  3. C. use of gypsum and lime mortars in making the inner surfaces of indigo vats water-proof.
  4. D. employment of slave labour in quick distilling of indigo curcibles.

Correct Answer: C. use of gypsum and lime mortars in making the inner surfaces of indigo vats water-proof.

Explanation

The use of lime and gypsum mortar provided a waterproof lining for vats, which was a significant technological improvement in the large-scale extraction of indigo dye.

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