Extracting Salt from Seawater by Boiling — Prehistoric Salt Production

Salt extraction by boiling seawater or brine from salt springs is one of the oldest chemical processes in human history, with archaeological evidence dating back at least 8,000 years at sites like the Poiana Slatinei salt spring in Romania and Duzdagi in Azerbaijan. Salt (sodium chloride) was critical for food preservation — salting meat, fish, and vegetables — and remained one of the most valuable trade commodities for millennia, giving rise to the word 'salary' from the Latin 'salarium' (salt money). Seawater contains approximately 35 grams of dissolved salts per litre, of which about 78 percent is sodium chloride. The process is straightforward in principle: collect seawater or brine, boil it in clay vessels or by hot-stone boiling in watertight containers, evaporate the water, and scrape the crystallized salt from the vessel walls. In areas far from the sea, people boiled water from salt springs (which can contain 10 to 26 percent dissolved salts — far more concentrated than seawater) or burned salt-tolerant plants such as saltwort (Salsola kali) and glasswort (Salicornia europaea), then leached the ash with water and evaporated the resulting brine. This blueprint teaches the hot-stone boiling method for extracting salt from seawater or brine, using only materials available to prehistoric coastal peoples.