Everywhere you look in Portugal (and frequently in Brazil and Cape Verde) you find Azulejo, painted ceramic tiles. Azujelo is from the Arabic Al-zullij, “polished stone.” Our guide on our Lisbon tuk tuk, tour, Maurice, told us they were developed by the Moors. He claims that the Moors painted mud bricks. When fire swept through towns, burning wooden roofs and building frames, the paint baked onto the bricks, accidentally creating tiles. Later, according to Maurice, they were used on the outside of homes to keep fire from spreading.

Some experts say the tiles originated in Egypt and moved west with Islam, some say they have an earlier Persian origin. And while I couldn’t find references to the tiles originating by accident, they do serve as fire protection. Tiles on the outside of buildings also reflect sunlight keeping the building cool. Tiles inside a building also have a cooling effect. This is the result of a process called passive radiative cooling. Passive radiative cooling happens when “The energy a material absorbs exceeds the energy it emits.” The tiles absorb heat during the day and do not release it until the temperature cools at night, keeping temperatures inside a space even.

Originally, the tiles bore geometric designs, without human forms, as befits an Islamic art form. Some of the earliest Arabic tiles repeated patterns the Arabs found in Roman mosaics.

In Christian Portugal and Spain they also became a medium for drawing scenes and depicting people. The blue tiles by Delft in Holland influenced the art form in Portugal in two ways. Blue became the most popular Portuguese tile color and the Dutch perfected a way of mass producing tiles that the Portuguese copied. These tiles are from a convent showing the atrocities that the conquering Moors inflicted on Christians during their conquest of Iberia.

Tiles are used in modern street art. Here is a sample from Lisbon.