Morocco is a hot, dry place. To work in a tannery in Marrakech is to work under some of the harshest working conditions there are. Not only are you exposed to the blazing sun, but you are are soaked in blood, animal bodily fluids and parts, pigeon poo, and get paid appallingly.But there is some science to the ancient Moroccan tannery tradition.Legend has it that the tanners are descended from demons who lived under a black king. As they didn't obey his rules, they were condemned to work in the tanneries. They use hundreds of concrete vats to process animal skins which are bought locally in the souks. The skins (mainly sheep and goat although cow and camel are sometimes used - lions are no longer used as they were hunted to extinction in the region around 1900) are treated far differently to the way leather is treated in other parts of the world as the process clings to its ancient traditions. Hair and flesh are removed by soaking the skins in quicklime (Calcium Oxide formed when limestone - calcium carbonate - decomposes) and water. After this, the skins are placed in a vat of water and blood, then separated and rung out, before being coloured using a few natural products:Pomegranate for yellow;Olive oil for shininess;Bark for various colours, presumably brown;Saffron for golden yellow;Henna for red/orange;Poppy for many other colours including white, pink, yellow, orange, red and blue.The skins are stretched out and left to dry for over 20 days in little piles that look rancid. Pigeon poo is used to soften the leather, and if anyone knows why, I would love to know. Presumably the poo is slightly acidic. Pigeon poo has actually been reported to be quite dangerous, with people almost dying after ingesting it. The poo adds to the smell of the place, with there being large pigeon coups near the top in which you could wade knee deep in the brown-smelly stuff. Tannery, Marrakesh, Morocco, 2010.