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It is commonly believed that the Crusaders brought Aleppo soap back to Europe in the 11th century, based on the claim that the earliest soap made in Europe was just after the Crusades, but in fact the Greeks knew about soap in the first century AD and Zosimos of Panopolis described soap and soapmaking in c. 300 AD. Following the Crusades, production of this soap extended to the whole Mediterranean area.
In the 17th century, the soap caused controversy in England, since it supplanted the unnamed local soap after the Spanish Catholic manufacturers purchased the monopoly on soap from the cash-strapped Carolinian government. Its ties to Catholicism caused a public-relations campaign to be established, featuring washerwomen showing how much more effective local soaps were than Castile soap. The sale of a monopoly in Protestant England to a Catholic company caused great uproar, ending with the Castile soap company eventually being stripped of the monopoly.
Early soap-makers in England did not have easy access to laurel oil and therefore dropped it from their formulations, thereby creating an olive-oil soap now known as Castile soap.
Importations of "Castile soap" through Antwerp appear in the London port books of 1567–1568, though the Oxford English Dictionary has no references to "Castile soap" earlier than 1616. In his article "A short history of soap", John Hunt maintains that barilla (an impure form of sodium carbonate obtained from halophyte plant ashes that were high in sodium) was boiled with locally available olive oil, rather than tallow.
Adding brine to the boiled liquor made the soap float to the surface, where the soap-boiler could skim it off, leaving the excess lye and impurities to settle out. While Aleppo soap tends to be green, this produced what was probably the first white hard soap, which hardened further as it aged, without losing its whiteness, forming jabón de Castilla.
- Soap (data) from Pharmaceutical-journal.com. Retrieved Oct 2014.
- "Aleppo Soap, The True Natural Soap". Natural Cosmetic News. Retrieved 2012-07-09.
- Partington, J. R. (1960). A history of Greek fire and gunpowder (Johns Hopkins paperbacks ed.). Cambridge: Heffer. ISBN 0-8018-5954-9. Retrieved 25 May 2015.
- Gregg, Pauline (1981). King Charles I. London: Dent. p. 218. ISBN 9780460044370. OCLC 9944510.
- Dietz, Brian, ed. "The Port and Trade of Early Elizabethan London: documents". London Record Society. Retrieved 25 May 2015.CS1 maint: extra text: authors list (link)
- John Hunt "A short history of soap"