1. Alkaline Ash
The key to Nablus soap is that it is cooked hot for a week or more to react all of the soda with the olive oil. And for this process to happen, an alkaline soda powder needs to be made to interact with the olive oil. For the first 1000 years or so, Nablus soap's soda mix was of barilla plant ashes and lime.
People for many thousands of years have used wood ashes or potash as a cleaning agent. Often such wood ashes were available from family and community hearths and furnaces, and washing with it enabled fats to become relatively soluble in water. What makes the potash effective as a cleaner is its relatively high PH, and ashes from hardwood trees were more effective than from softwoods at producing a strong potash.
For makers of soaps, however, it is crucial to make alkaline water of a very specific strength so that it chemically interacts predictably and effectively with the acidic oil base. Moreover, if the soapmaker wants a hard, rather than liquid, soap, salt needed to be added to the potash, and the potash itself needed to be used in great quantities to make a lye solution of acceptable strength. Soapmakers, glassmakers, papermakers, and other artisans needing strong alkaline substances to produce their goods, needed caustic potash also known as caustic soda. Caustic refers to a potash that is so strong that it burns the skin upon contact.
Mediterranean artisans had long ago discovered that ashes from certain seaweed plants which grew along the shores of salty water bodies were superior to hardwood ashes for the making of caustic potash. (In Northern Europe certain kelps were also sometimes used). The best of these seaweeds was known as barilla. Barilla, as its scientific names Salsola soda and Salsola kali indicate, produced a strongly alkaline-salt-bearing potash. A thousand years ago this plant was so economically important in the Mediterranean that it is hard to imagine today. By the 1800s in Spain, one could be punished with death for smuggling barilla seeds without the right permits. And in Nablus the trade in barilla ashes, known as qilw, were carefully monopolized by local Bedouin.
2. Qilw in Nablus
The Brown University historian Beshara Doumani recounts in his history of soapmaking in Nablus that soapmakers used about 1000 pounds of qilw to make one batch (tabkha) of soap. He writes that,
Until the introduction of caustic soda in the 1860s, large numbers of bedouins from the Bani-Sakhr, Huwayatat, and Adwan tribes gathered barilla in the valleys of M`an, especially around Salt and Tadmur (Palmyra). In the summertime they piled these plants in towering stacks, burned them, gathered the ashes and coals into sacks, and carried them to Nablus in large caravans.
Burckhardt witnesses this process in 1812, and had this to say about the complex reciprocal obligations built around the qilw trade and other economic contacts with bedouins:
``The Arabs of the Belka [Balqa], especially the Beni Szakher [Bani Sakhr], bring here Kelly or soap-ashes, which they burn during the summer in large quantities: these are bought up by a merchant of Nablous, who has for many years monopolized the trade in this article. The soap-ashes obtained from the herb Shiman, of the Belka, are esteemed the best in the country…They are sold by the Arabs…but the purchaser is obliged to pay heavy duties upon them. The chief of the Arabs of El Adouan…exacts for himself five piasters from every camel load, two piasters for his writer, and two piasters for his slave. The town of Szalt [Salt] takes one piaster for every load, the produce of which duty is divided among the public taverns of the town. The quantity of soap-ashes brought to the Osha market amounts, one year with another, to about three thousand camel loads. The Nablous merchant is obliged to come in person to Szalt in autumn. According to old customs, he alights at a private house, all the expenses of which he pays during his stay; he is bound also to feed all strangers who arrive during the same period at Szalt; in consequence of which the Menzels [public taverns] remain shut; and he makes considerable presents on quitting the place. In order that all the inhabitants may share the advantages arising from his visits, he alights at a different house every year.''
Burckhardt‘s observation that three thousand camel loads were sent to Nablus annually in the early nineteenth century seems to be fairly accurate. Each tabkha of soap required at least 7 camel loads, or qintars of qilw. Because Nablus soap production ranged, at the very least, from 100 to 400 tabkhas a year, a minimum of 700 to 2,800 camel loads arrived in Nablus annually. Merchants from Nablus and the town of Salt also exported qilw to nearby soap- producing centers, such as Gaza, Jaffa, Lydda, Jerusalem, and Acre. Nablus merchants put conditions on the type and quality of qilw as well as on the time of delivery. According to Nimr, caravan shaykhs expected, in return, a certain percentage of the overall price as commission upon delivery, as well as some gifts in kind. For instance, Nimr claims that for every 100 camel loads, the caravan leader received money plus one large basket (quffa) of rice, as well as one ratel each of tobacco, sugar, soap, and coffee. He also received a cloak, a pair of boots, and a fur saddle blanket.
3. Barilla today
Barilla stills grows across the Mediterranean and along all the shorelines of the United States, but since the late 1800s when industrially-produced caustic soda came into production barilla has been largely forgotten and considered by many to be just a weed. Today the most popular use for it is as a spinach-flavored green in Italian cuisine, where it is known as agretti. In parts of the English speaking world it is known as saltwort.
It's hard to overstate the importance of soda ash in the ancient Mediterranean world. The first known soap recipe is recorded on a 4500 year old clay tablet from modern-day Iraq and Kuwait (at the time the polity of Babylon) — it calls for the same recipe still used by artisans today: ash, olive oil, and water. The words sodium and soda come from the Arabic sauda, just as sodium's name (Na) in the periodic table of elements refers back to a version of soda-ash called natron used by the Egyptians in papermaking, mummification, and soapmaking.1 The word ``alkaline'' reaches back to the Arabic root al-qaliy, meaning ``burnt ashes.''2, and the barilla plant still bears its history in local names such as ``soapmaker's bush'' (almajo de los jaboneros) and ``maritime soda plant'' (sauda maritima) in Spanish. The popularization and commercialization of soaps — called sebum, meaning tallow or animal fat, in Latin — during the Roman Empire — still resonates in many languages today, from the Arabic sabun to the Spanish jabón and French savon to the old Dutch seepe and English sãpe.
Sala Caja, Lidia. "La competencia terminológica: causas lingüísticas en el auge del término sosa y el declive de barrilla en los siglos XVIII y XIX." Asclepio (2003): 67-92.