labu
FROM pots, gourds, the local 'labu' and the amphoras of ancient Greece, clay has long been used to store everything from grain, water – and the case of the amphoras – wine.
Nowadays, most people might have 'labu' lying around the house as a decoration or a hand-me-down from their grandparents but not many use these receptacles for their original intended use, which is to store stuff.
However, folks back in the day swore that their clay labu cooled boiling water faster than leaving it in the pot.
Is it true that clay gourds can cool water?
Verdict:
TRUE
As surprising as it may sound, clay gourds are really very good at cooling down water. Not only that, clay pots in general are very good at cooling down almost anything!
There is a caveat, however – the clay has to be unglazed in order for it to achieve its maximum cooling effect.
Clay by its nature is a porous material.
A clay gourd is made from, well, clay, which is a mixture of a particular type of fine grain earth and clay minerals mixed together with water, shaped into the required shape and then fired in a kiln.
The process of firing the kilns drives out most – if not all – of the moisture in the gourd, leaving behind microscopic gaps in the now-hardened clay.
These pores are very small, too small for water to leak out of the gourd when you fill it up (otherwise it would be useless for storing liquids) but are large enough that some water can actually seep to its surface.
This water will then evaporate and in the process, cools down the gourd along with its contents.
As mentioned earlier, this only works with unglazed vessels as the glaze seals up all the little pores, thus preventing any evaporation from happening.
With enough ventilation around the receptacle, you could theoretically cool the water down to wet-bulb temperature, which in Malaysia is at about 26°C to 27°C. Not frosty cold, but definitely cooler than our usual 30°C to 33°C.
References:
1. https://iopscience.iop.org/article/10.1088/1757-899X/1107/1/012103/pdf
2. https://www.sciencedirect.com/science/article/pii/S2214157X21001854
