One of the earliest uses of soap was to prepare wool for weaving. Later, soap began to be an elemental part of bathing, and soap-making guilds became prominent in Italy and Spain. Soap-making was sometimes considered “women’s work”, although as it became a prized commodity the skill became one of craftsmanship, with one soap-maker trying to outdo the next with softening agents.
Gradually, coloring agents and perfumes were added, and soap was sold in both liquid and solid forms. Marseille and Castile soap are made from mostly olive oil, and are considered more pure than those with harsher chemicals.
A soap bar cost about one-third of a dinar (dinero, denier) in the tenth century.
A Persian chemist wrote recipes for making soap, as did other soap-makers. Here is a recipe from a 13th century document:
Take sesame oil, a sprinkle of potash, alkali, and some lime, mix together and boil. Pour into molds and leave to harden.