Manual of soap

Coalescence IV  (oil on linen) © Matthew Johnson (Olsen Irwin Gallery)

Coalescence IV (oil on linen) © Matthew Johnson (Olsen Irwin Gallery)

Soap was already in use a thousand years before the Christian era. Similar cleaning solutions were used in Mesopotamia several thousand years before that. It has changed in shape and composition, its variations are legion, but soap still has the monopoly in global hygiene.

So what did soap look like over all these years, when its ingredients are never the same, and neither are its uses? Soap is a composite whose compounds at one end attract water and at the other attract fats. When stirred (with water if it is solid) this aggregate of molecules with its contrary properties lathers and makes bubbles: in this unstable state, these so-called amphiphilic molecules retain the fats on one side (in this case, the dirt) and combine with water on the other. And we’re clean. But these bubbles had generations of scientists in turmoil, leaving them high and dry, or even in dirty water. These compounds come from a reaction known as saponification. This uses fatty acids (animal fats, plants, vegetable oils, etc.) and metallic salts (soda or potassium hydroxide, or caustic potash), often by hot process. Then come various operations and additives to form soap: an infinite variety, solid, liquid and scented. Although saponification was known and implemented for thousands of years and in thousands of ways, it was not until 1810 that Michel-Eugène Chevreul (him again!) managed to report its chemical process, hydrolysis. Thus began the industrialisation of soap (19th century) and the invention of synthetic compounds (20th century). But the word soap includes all the industrial washing products, or detergents, made in the petrochemical industry.

In the empires and dynasties located between the Tigris and the Euphrates, then in Egypt, washing paste was cooked, made of fats – vegetable oil or animal fat (tallow), white salt, ash and clay. In Syria, soap from the town of Aleppo made of olive oil, soda and bay tree berries was famous long before our time, and sold in the Mediterranean gulf.

With the coastal waterways between the Middle East, Italy and Spain, Marseille became a hub for shipping raw materials. Craftspeople from all countries came there, and the city became a centre for soap. With its olive trees, sea salt and alkali (or ash) from Camargue, the Provence region provides the best raw materials for the soap industry. And yet everyone, from the Arabs and Turks to the Vikings, made soap in their different ways. It was mainly used for washing fabrics or in public baths.

Water was long suspected of spreading infection, and was not allowed to be used for washing people. Baths reappeared in Europe in the late 18th century, but did not become a hygiene habit until the following century, when cleanliness became a moral value, taught at school and in the army. Soap gradually came into the picture… For the record, when the Austro-Hungarian obstetrician I.P. Semmelweis demonstrated in the latter half of the 19th century that it was necessary to wash one’s hands between dissecting a corpse and delivering a baby to reduce the number of maternal deaths from puerperal fever, he had the whole medical community against him; he was not proved right until after his death. Graphs comparing the use of soap and incidences of infant mortality have since shown the importance of hygiene, and first in the fight against epidemics.

The vast history of soap spans several eras, and probably all the continents and all cultures. Today soaps have become one of life’s pleasures, a beauty treatment that feeds, softens and perfumes the skin. But one essential law of chemistry remains: the more it lathers, the cleaner it is.