By Porter Lang
Check the glaze first. A glazed jar looks the same on a shelf, and it will not cool anything. That is the most useful point in the sources, and it comes from the blog.
What it is
Wikipedia calls the botijo, also known as the búcaro, a traditional porous clay water container typical of many parts of Spain, in varying shapes and colours. It lists regional names: cà ntir and botija in Catalan, botico in Aragonese, canabarro in Galician and txongil in Basque. Low-tech Magazine, a blog about older technologies, in a 2012 post, treats the same object as one of a family of unglazed clay coolers found around the Mediterranean and in the Indian subcontinent, where it names them ghara, matka and suhari.
The parts
Wikipedia gives a wide belly, one or more filling openings, and one or more spouts, called the pitón or pitorro, for drinking. The Low-tech Magazine post gives a wide, spherical belly with two openings on top, one wide for filling and a smaller one for drinking, and one or two handles. After filling, it says, the large opening is covered with a cork or cloth to keep insects out. The post gives a typical capacity of about three litres and up to seven for large ones, and an average filled weight of about 4.5 kilograms.
Why it cools
The clay is unglazed and porous. Water seeps through the walls and evaporates in the outside air, and the evaporation pulls heat out of the water inside. Wikipedia gives a figure of 2.219 kilojoules per gram of evaporated water. Low-tech Magazine compares it to the way the body cools itself by sweating. A glazed jar seals the pores, so the water cannot escape, and nothing cools. Low-tech Magazine and its repost say the jar must be unglazed to work, and that glazed versions are often sold as tourist souvenirs. Wikipedia says only that the clay is unglazed and porous.
What the numbers say
Low-tech Magazine reports a test of a 3.2-litre botijo at 39 °C and 42 per cent relative humidity. After 15 minutes the water was 2 °C cooler. After one hour, 8 °C. After three hours, 13 °C. After about seven hours it reached 24 °C, with about 0.4 litres, 8 per cent of the water, lost, and then slowly warmed again. At outside temperatures around 30 °C, it says, cooling is limited to about 10 °C. It cites a 1995 experiment showing up to 15 °C of cooling under optimal conditions. The post says the jar works best in shade but also works in sun or indoors.
Where it works, and where it does not
Low-tech Magazine says cooling weakens in humid summers, because the water cannot evaporate in hot, humid air. It suits hot, dry summers, including Mediterranean and desert climates. In Spain, it says, the north-west has no tradition of evaporative coolers and uses glazed containers, and coastal Mediterranean areas also favour glazed containers because the sea raises the humidity. This is a source’s generalisation, and the other source says nothing on it.
How old it is
Wikipedia says the oldest botijo found on the Iberian Peninsula belongs to the Argaric culture. It came from the Puntarrón Chico necropolis at Beniaján, near the capital of the Region of Murcia, and is held by the Archaeological Museum of Murcia. It has a single 2-centimetre hole and a handle on top and measures 11 by 9.5 centimetres. Low-tech Magazine says the cooler probably originated in the Indus Valley Civilisation about 5,000 years ago. Those are two different claims about two different things, one an object and one an idea, and we set them next to each other without joining them.
Reading the test
The temperature figures come from one jar of 3.2 litres in one set of conditions, 39 °C and 42 per cent humidity. The post does not say who ran the test, where, or on what clay. Our reading: the pattern is probably the useful part, a steep drop in the first hours and then a plateau, and the exact degrees should not be taken as a promise for any other jar. The post itself says cooling shrinks as the air outside gets cooler or more humid.
Dates in order
- About 5,000 years ago: the probable origin of the clay cooler in the Indus Valley, according to Low-tech Magazine.
- 1926: the date of a source cited for the cooling explanation, according to Wikipedia.
- 1995: an experiment showing up to 15 °C of cooling, according to Low-tech Magazine.
- 2012: the date of the Low-tech Magazine post.
Side by side
Both sources describe the same mechanism, and the blog adds the warning about glaze. They differ on emphasis: one lists names and an archaeological find, the other lists measurements and climates. Our reading: neither is a maker’s account, so neither tells you how a particular jar was fired or what clay it uses. No source describes the clay or the wall thickness.
What kind of sources these are
Wikipedia, which flags this article as needing additional citations, and a blog post from 2012 about low-technology, which we read through its repost on No Tech Magazine as well. We read no museum page and no potter’s page.
Questions a buyer would ask
Is it glazed or unglazed? How many litres does it hold, and can you carry it full at around 4.5 kilograms for a three-litre jar? Is the climate where it will sit dry or humid? Is it shaded? The sources give no breaking-in instructions and no care advice, and we offer none.
What we left out
We left out a fragrant Mexican clay vessel that Wikipedia mentions, because we found nothing further on it. We left out any claim about the health of cool water against cold, which the blog makes as an argument and gives no evidence for. We left out suspended and tap-fitted versions, prices, and every maker.
Roam first. Shop later.