A salt crystal is seawater minus most of its water. What remains is sodium chloride, mostly, with small fractions of calcium, magnesium, potassium, and trace elements that vary by where the water sat and how long the sun and wind took to drive the moisture off. Hold two crystals, one pulled from a Breton pan, one from a Sicilian one, and the differences are quieter than the labels suggest. But they are there, and they begin with temperature.
The pace of evaporation
Sea salt is made by letting seawater go. The mechanism is the same everywhere: water flows into shallow basins, the sun and wind take the moisture, and salt concentrates until it crystallises. What changes from place to place is the speed.
The Atlantic, off Brittany and the west of Ireland, is cold. Evaporation runs slow there, helped along by wind more than heat. The season is short and the yields are modest. Crystals that form slowly in cooler conditions tend to be finer and more irregular, and they hold more of the residual brine, the mother liquor that carries magnesium and calcium salts alongside the sodium chloride.
The Mediterranean works faster. In Trapani, on Sicily’s west coast, and across the Camargue in southern France, summer heat is high and the air is dry. Water evaporates quickly, crystals form quickly, and the harvest is larger and more reliable. Faster crystallisation tends to produce a cleaner sodium chloride crystal, less brine trapped, a slightly different mineral fraction left behind.
This is the whole of it, mechanically. Cold and slow against warm and fast. Everything else, crystal shape, mineral profile, the marketing, follows from that.
Fleur de sel, and what sits on top
In both regions there is a surface salt and a pan salt, and they are not the same product.
Fleur de sel, “flower of salt”, is the thin, fragile crust that forms on the surface of the brine on still, dry days, before the heavier crystals sink. It is raked off by hand from the top of the pans, in Guérande on the Atlantic side and in the Camargue and around Trapani on the Mediterranean. It is finer, flakier, and holds more moisture than the coarse salt harvested from the bottom. Its mineral content is marginally higher because it forms from the most concentrated surface layer.
The coarse grey salt below, sel gris in Brittany, harvested from clay-lined pans, picks up trace minerals and a grey cast from the basin floor. It is denser and wetter and is what most coastal salt economies actually run on.
Neither region holds a monopoly on either grade. The distinction that matters to a maker is less Atlantic-versus-Mediterranean than surface-versus-pan, fine-versus-coarse.
The mineral question, honestly
Here is where most sea salt sourcing claims overreach. Atlantic sea salt is often described as richer in minerals, and Mediterranean salt as cleaner or purer. There is a kernel of truth, cooler, slower Atlantic evaporation does tend to leave more residual magnesium and calcium in the crystal, but the differences are measured in fractions of a percent. Sea salt of either origin is overwhelmingly sodium chloride. The trace minerals that distinguish a Breton harvest from a Sicilian one are present, real, and rarely the headline a buyer imagines they are.
This is worth saying plainly because the salt trade does not say it. Mineral content is the easiest thing to dramatise and the hardest to perceive. In a finished soap, where salt is one component among oils, water, and lye, the difference between Atlantic and Mediterranean trace minerals is not something skin reports back. What the salt does, and it does it regardless of which sea it came from, is harder to overstate.
What salt does in a bar
Sodium chloride hardens soap. It reduces water activity in the bar, which makes it denser, longer-lasting, and slower to dissolve. It also cuts lather, which is why salt bars feel different in the hand: less foam, a creamier, almost waxy slip, and a dry finish on the skin once rinsed. Salt is exfoliating at the coarse end and conditioning at the fine end, and it cleanses as part of the soap matrix rather than on its own.
These behaviours come from the chloride, not the provenance. A bar made with Mediterranean salt and a bar made with Atlantic salt of the same grain will perform almost identically. The choice of origin is, in honest terms, a choice about supply, grain size, and the story you are willing to tell about it, and we would rather not tell the inflated version.
The way salt reshapes a bar’s character is closer to how a base note reshapes a fragrance than most people expect: structural, quiet, felt more than noticed. The same is true of dry woods in scent, the austere, long-lasting quality of Atlas cedarwood does its work underneath, where you stop registering it as a separate thing. If you want the longer account of how that cedar behaves and why its name is misleading, the trees it doesn’t name covers the confusion in full, and the pencil you already remember describes the scent itself.
What we use, and where it comes from
Saltstone is built around Atlantic sea salt. The reason is not a claim about superior minerals, we have just spent several paragraphs declining to make that claim. The reason is provenance and grain. The studio sits on a coast in the west, on the Atlantic, and the salt is sourced from cold-water evaporation in the same body of water the studio looks out on. The grain is chosen for how it sits in a cold-process bar: enough to harden and to register against the skin, not so coarse that it scratches.
That the salt and the studio share an ocean is a fact, not a virtue. It does not make the bar perform better than one built on Trapani salt would. It makes the sourcing path short and the origin honest, which is the most a sourcing story should claim.
Two seas, then, and two salts that are more alike than the marketing of either would have you believe. The Atlantic is colder and slower and leaves a touch more behind. The Mediterranean is warmer and faster and yields more. In the pan, the difference is real. In the bar, it is small, and the salt does its work either way.