text: Before the invention of artificial refrigeration technology, ice making by nocturnal cooling was common in both India and Iran.
  In India, such apparatuses consisted of a shallow ceramic tray with a thin layer of water, placed outdoors with a clear exposure to the night sky. The bottom and sides were insulated with a thick layer of hay. On a clear night the water would lose heat by radiation upwards. Provided the air was calm and not too far above freezing, heat gain from the surrounding air by convection was low enough to allow the water to freeze.
  In Iran, this involved making large flat ice pools, which consisted of a reflection pool of water built on a bed of highly insulative material surrounded by high walls.  The high walls provided protection against convective warming, the insulative material of the pool walls would protect against conductive heating from the ground, the large flat plane of water would then permit evaporative and radiative cooling to take place.