The art of pottery is deeply rooted in African culture. In northern Nigeria, earthenware pots have been used since ancient times as cooking and water storage vessels, coffins, wardrobes and banks. Today, these clay pots are almost extinct, replaced by aluminium containers and more modern methods of burying the dead, storing clothes and saving money.
Born in 1964 into a family of pot makers and raised in the rural north, Mohammed Bah Abba was familiar from an early age with the various practical and symbolic uses of traditional clay pots, and learned as a child the rudiments of pottery. Subsequently studying biology, chemistry and geology at school, he unravelled the technical puzzle that led him years later to develop the "pot-in-pot preservation/cooling system".
He was selected as a Rolex Laureate in 2000 for this ingenious technique that requires no external energy supply to preserve fruit, vegetables and other perishables in hot, arid climates. The pot-in-pot cooling system, a kind of "desert refrigerator", helps subsistence farmers by reducing food spoilage and waste and thus increasing their income and limiting the health hazards of decaying foods. Abba says he developed the pot-in-pot "to help the rural poor in a cost-effective, participatory and sustainable way".
The pot-in-pot consists of two earthenware pots of different diameters, one placed inside the other. The space between the two pots is filled with wet sand that is kept constantly moist, thereby keeping both pots damp. Fruit, vegetables and other items such as soft drinks are put in the smaller inner pot, which is covered with a damp cloth. The phenomenon that occurs is based on a simple principle of physics: the water contained in the sand between the two pots evaporates towards the outer surface of the larger pot where the drier outside air is circulating. By virtue of the laws of thermodynamics, the evaporation process automatically causes a drop in temperature of several degrees, cooling the inner container, destroying harmful micro-organisms and preserving the perishable foods inside.
Universal technique
The principle of physics used by the pot-in-pot is present in nature itself. A panting dog, for example, uses the same process, losing heat through its tongue. It is also well known by humans in arid countries. Indeed, the roots of innovation spread wide and deep, and Abba’s pot-in-pot is one of several ingenious applications of cooling by evaporation.
The city of Qena in Upper Egypt is renowned for its porous-clay cooling vessels – a tradition spanning more than three millennia. In Burkina Faso, the Jula people’s traditional jars are sometimes soaked in water before goods are stored in them, so that they stay cool by evaporation. This single-pot design is similar to the pot-in-pot, but less efficient.
In India, street vendors often cool fruit or drinks for their customers by suspending bags of produce in a porous clay container. Also in India, a rectangular enclosure of wet bricks is used to preserve foodstuffs from heat. Water seeps slowly through the porous bricks, evaporating from the surface and keeping the entire structure cool. The Punjab Agricultural University in Ludhiana has recently tested an improved version of this system, which is closer to the pot-in-pot than any other device. It uses double-brick walls, with wet sand between them. The sand is kept wet, and the entire chamber is covered with a moist mat. Fruit and vegetables inside the chamber are maintained at temperatures below 20° C.
In 1992, laboratory experiments to measure the temperature drop in a two-pot design, where a small clay receptacle is placed within another receptacle filled with water, were carried out at the University of Benin City by Nigerian professor Victor Aimiuwu. He found that the device had good cooling properties, remaining up to 14 degrees cooler than the surrounding environment.
Putting theory into practice
Still, among all the similar devices and traditional cooling pots, there is nothing quite like the pot-in-pot with its unique combination of simplicity and effectiveness. In fact, the Nigerian teacher’s project shows how, for the Rolex Awards, originality is far more than a bright idea – it means turning an inspiration into a concrete achievement with a major impact.
"Mohammed Bah Abba won a Rolex Award not simply because he designed the pot-in-pot. He overcame obstacles to produce and distribute it, and also ensured that it could be bought for an affordable price by the people who need it," says Rebecca Irvin, head of the Rolex Awards Secretariat in Geneva.
To understand the relevance of Abba’s Rolex Award-winning project, it is necessary to look at the geography of northern Nigeria and the restricted lives led by the people. This region is primarily a semi-desert scrubland inhabited by a large, mostly agriculture-based population, the majority of who live in abject poverty. Polygamy is a dominant feature of the family structure, a