History of soap, defined here as a product of saponification reaction between the fatty acids and lyes reach quite far back, as the first attested knowledge and usage of the substance dates back to 23rd century BCE, as evidenced by the clay tablets found in Babylon, then a minor city in a newly formed Akkadian Empire. Similar documents from the Middle East and Northern Africa also indicate that the soap production was quite common in Ancient Mesopotania, Levant and Egypt with both plant and animal oils being used, as well as the mineral and plant-based alkali. Traces of the latter distinction can be also found in the Old Testament (Jer 2:22), where both neter (נֶתֶר) and borith (בֹּרִית) are mention, corresponding to natron (mineral sodium carbonate used in e.g. process of mummification in Ancient Egypt) and lye made from ashes respectively, with both being indicated as either cleaning substances or a shorthand for it. It is also possible that the lyes were initially used to clean wool, as they could react with lanolin, forming water-soluble soap that would make it easier to remove natural secretions from wool. This observation might have led to the deliberate production of soap from alkali and natural fats. Another common theory says states that people could have observed that the fat falling from roasted meat into the ashes formed a substance that was useful in cleaning and washing. As with any early invention, we will possibly never know the details.

The production of soap was quite possibly well known among the inhabitants of the northern part of the continent as early as 1st century CE, what is suggested by Pliny's remark in his Historia Naturalis (book XXVIII, ch. 51), where he attributes the invention of soap to Gauls and notes its usage across Gauls and Germans, stating that soap is made there either as a solid or a liquid. On a side note, Pliny uses the word sapo (soap) causally (the chapter speaks of remedies for the tonsil ailments and scrofula), indicating that the product itself must have been nown in Roman Empire, even if ot hasn't been widely used for personal hygiene. Not having direct access to the olive oil, ubiquitous in the Mediterranean, Germans and Gauls were generally using tallow or lard as the main ingredient what could have also meant that the soap could have at least somewhat unpleasant smell, at least as far as modern sensibilities go. And while we're at that issue, it is worth noting that the soaps made from olive oil could have also retained specific smell of the latter, but the evidence of adding fragrant substances is attested roughly as early as the first evidence of the soap making, with Akkadian and Sumerian recipes mentioning cassia oil and other fragrant substances.

One of the alkaline substances commonly used to produce soap is though to be potash i.e. potassium carbonate (K2CO3) that can be either mined as naturally found potassium salt or produced from It should be mentioned here that the same 'potash' is now applied to various potassium compounds and the potassium carbonate itself is usually referred in English as 'pearlash', although the difference is generally far more ambiguous in older sources. Additionally, in other languages, most notably Germanic and Slavic, the term 'potash' and its derivatives denote specifically this particular salt. Its name is commonly attributed to the German term Pottashe (lit. pot ash) alluding to the early method of production by burning the organic material in a container and then leaching the resulting ashes with water. Furthermore, by addition of calcium hydroxide (caustic lime) to the solution of potassium carbonate one can obtain a relatively insoluble calcium carbonate and the solution of potassium hydroxide, a strong lye that is even more conducive to saponification. It is very likely that this process was, consciously or not, used in the production of soap in the Middle East, as the recipes from 9th-11th centuries often mention lime as an important ingredient along the potash and natural oils.

Although the common use of potassium salts in the process of saponification would suggest that the resulting product was relative soft and resembling more a balm rather than a hard bars (potassium soaps tend to be softer and more liquid than sodium ones), the main alkaline substance obtained from leaching ash of some plants could have been also sodium hydroxide, especially in case of plants notable from storing large quantity of sodium, usually halophytes such as saltwort (Salsola) or saltbush (Artiplex), quite common in the arid areas near estuaries and shorelines. As for the process of soap-making itself, it usually involved cooking oils or fats in a vat with the addition of lyes and other substances (like fragrances, seawater or lime) until the mixture started to trace, i.e. turn from liquid into semi-solid form. We can only guess that with the hit-an-miss approach to the production due to lack of chemically clean lyes soaps final products could have often contained had some unsaponified fats or excessive amount of alkali, although experienced soapmakers knew how to minimize these shortcomings.

Potash or more specifically pearlash has been produced on a relatively large scale in asheries, usually located closely to other facilities processing wood, such as charcoal kilns. Judging from the topographical names in Central Europe, in Middle Ages and Early Modern period there were many villages focusing on the production of this particular material, most often than not a servitorial settlements bound to provide the local landowner with the specific goods or services. As one can easily guess, regions known for their wood exports were usually also notable exporters of potash, as was the case of Poland, Lithuania and Russia.

Between the widespread use of soap in continental Europe, the Middle East and eventually also the Roman Empire, traditions of soap-making continued into Early Middle Ages, with the southwestern continental Europe (modern southern France and northeastern Spain) becoming the area best known or their soaps what can be possibly attributed to strong Gaulish traditions and easy access to both plant, mineral and animal ingredients. With the Ummayad conquest of the Iberian Peninsula and introduction of Arabic methods of soap production, Spain became the biggest European producer of soap in the Middle Ages. European medieval soaps made in that region were usually scented with local fragrant plants such as lavender or wormwood. Both in Europe and Middle East soap was generally considered an all-around useful item, leading to the emergence of the large manufactories (we can't speak of factories or industries in modern sense yet) around late 12th or early 13th centuries to meet the demand for the product.

So, to sum it up, soap in an ancient invention used for at least 4500 years and possibly longer, originating in Mesopotamia but very likely developed independently in other parts of the world. It has been and often still is made from plant or animal fats and lyes produced by leaching ashes, preferably from the plants containing large amounts of potassium and sodium salts, which process has been replaced in late 18th century by the industrial production of chemicals.