A coastal community makes salt from seawater either by letting the sun and wind evaporate it in shallow ponds in a warm, dry climate, or by boiling it in pans over fire where the climate is cloudy, cold or wet. Seawater is only about 3.5% dissolved salts and less than 3% sodium chloride, so every pound of salt costs about 35 pounds of water evaporated, and fire costs far more than sun.
Part of Salt Production & Sourcing
Seawater salt production is the making of food salt by removing the water from seawater, by sun in shallow ponds or by fire in boiling pans.
Two Routes, Chosen By Weather
Solar evaporation works where there is strong sun, steady wind and little rain. Seawater is let into shallow ponds above the high-tide line, sealed with clay, and left for days or weeks. In stages the water evaporates, and crystals form on the bottom of the last pond to be raked up. It costs labour and land but almost no fuel (Solar evaporation ponds).
Boiling works anywhere there is fuel. Seawater is boiled in wide, shallow pans until crystals form. It is independent of weather but burns a great deal of wood, which is why, as the parent notes, coastal salt was one of the most traded commodities in history (Boiling method for cloudy climates).
Either route follows the same chemistry: the water leaves, the sodium chloride crystallises, and the bitter magnesium salts stay behind (Seawater evaporation).
The Numbers In Brief
- Seawater is about 3.5% dissolved salts by weight (parent); about 78% of that, about 2.74% of the water’s weight, is sodium chloride (worked out in the evaporation article).
- To make 1 lb of sodium chloride, you must evaporate roughly 35 lbs of water: (100 − 2.74) ÷ 2.74 = 35.5.
- Boiling needs about 2,000 to 4,100 lbs of wood per 100 lbs of salt (worked out in Yield calculations).
The parent’s figure of 70 lbs of salt per ton of seawater counts all the dissolved salts, not just sodium chloride, so the common salt recoverable is lower. Details are in the yield article.
What You Need
- Clean seawater from open coast
- Ponds, or pans and fuel
- Rakes and baskets, drying racks, and covered storage
- Time: days to weeks per pond, and a season’s planning
Method: Choose A Route
Step 1: Judge your climate: how many sunny, dry, windy weeks you have, and how much rain falls in them.
Step 2: If the season is long enough for ponds, use them and keep fire as a backup.
Step 3: If not, plan for boiling and a firewood supply that can bear the load (Coppicing & Fuel Management).
Step 4: In either case, purify the crude salt before eating it.
Common Mistakes
- Expecting 70 lbs of salt per ton as pure sodium chloride.
- Starting solar ponds with no plan for a rainy spell.
- Boiling without counting the wood.
Safety
Heat, sun and salt water
Boiling brine scalds; ponds are a drowning risk for children; and long days raking salt in strong sun cause heat illness and, from the glare off salt crystals, eye damage. Use eye protection and keep drinking water at hand. Do not drink seawater.
What’s Next
- Learn next: Solar evaporation ponds — the cheap route in detail
- Combine with: Purification & Grading — what to do with the crude crystals