Homemade sea salt. (Deb Lindsey/FOR THE WASHINGTON POST)

Watching water evaporate is exactly as exciting as watching paint dry — it’s even the same principle — but that’s just what my husband, Kevin, and I found ourselves doing the first time we made our own sea salt.

It was a project born of a lack of other projects. We’d moved from Manhattan to Cape Cod the year before and were trying to glean much of what we ate from the world around us. There’s precious little to glean in February, though, and we were spending all too much time staring at the fire in the wood stove, waiting for spring. On top of that wood stove was a cast-iron pot with a lattice top, the kind that everyone who heats with wood fills with water and uses as a crude humidifier.

And then, just like in the cartoons, the light bulb went on over my head. It even made that noise. Why don’t we fill the pot with seawater and make our own salt? Genius! Or what passes for it on Cape Cod in February.

Kevin was skeptical. “So, we take the time, make the effort, and use the gas to drive to beach for, what, three tablespoons of salt, retail value seven cents?”

He had a point. We’d learned, the hard way, how much DIY food can cost. We’d raised the world’s most expensive turkeys, caught the world’s most expensive lobsters and grown the world’s most expensive potatoes. A little math was in order.

Seawater is about 3.5 percent salt by weight, which means a gallon of water (eight pounds) should yield about 4.5 ounces of salt. “If we fill our four-gallon stockpot,” I told Kevin, “we’ll end up with over a pound. That’s worth more than the half-gallon of gas we’d use getting the water.”

“And what’s your time worth?” he asked. As a writer, I know better than to answer. I put the stockpot in the truck, and Kevin resigned himself to the project. We drove out to Sandy Neck, a beach on Cape Cod Bay. I wouldn’t have thought wading could be harrowing, but big waves of ice-cold water can be disconcerting, particularly when you’re wearing waders, which can drag you under if they fill with water. We hear, regularly, of people drowning that way. I got my four gallons and got out, fast.

Our water was a little cloudy, and we ran it through a coffee filter to get out the sea shmutz: particles of seaweed or decomposing creatures or who knows what. We suspected our water also had a robust population of microorganisms, but we weren’t worried about them; they would die as evaporation made their habitat progressively less hospitable. Some pollutants would undoubtedly survive, but we figured the quantities were small enough that we needn’t be concerned. In the history of the world, I don’t think anyone has ever gotten sick from sea salt.

We replaced the humidifier with a 9-by-13-inch enameled cast-iron pan, because more surface area means faster evaporation. We filled it, and we waited — in our well-humidified home. When the water level went down, we refilled it. In a few days, the stockpot was empty.

And that’s when we found ourselves glued to the wood stove, fascinated by the process by which paint dries.

First, the water got cloudy. Then, when the solution was fully saturated, salt particles began to separate out, just like my seventh-grade chemistry said they would. They formed a skim coating on the surface; it thickened and sank. Eventually, the water was gone and we were left with a pan of beautiful, pure-white sea salt. Like magic. Understanding that seawater is 3.5 percent salt, and that the salt will be left after you evaporate the water, will not stop you from marveling as something materializes from nothing.

It will start you marveling, though, that the stuff is so expensive. Why would anyone pay $9 an ounce for what washes up on our shores for free?

Back in the day, before the twin miracles of canning and freezing, when salt was the only viable way to make fish, meat, or vegetables last more than a few days, it made sense that it was expensive. A mineral that stands between humans and starvation is about as valuable as a mineral can be. Now, though, our salt needs are small. We need enough for our bodies (about half a gram a day). We definitely need enough to make bacalao, and maybe a little extra to rub in other people’s wounds, but that’s it. Which is why ordinary table salt costs pennies per pound, and ordinary kosher salt just a little more.

What is it, then, about sea salt that makes it cost, ounce for ounce, as much as wild salmon or Kobe beef or chanterelle mushrooms?

It’s not the gas, or the writer’s time. It’s the minerals and the mystique, heavy on the mystique.

Sea salt marketing copy breaks down into two basic claims: Sea salt is a) better for you and b) better tasting. Both of those claims are based on its mineral content.

First, the health angle. When evaporate seawater evaporates, sodium chloride isn’t all that’s left. There are trace minerals as well, but the operative word is “trace.” Chemical analysis reveals that, other than sodium chloride, sea salt is about 4 percent magnesium and 1 percent each calcium and potassium (by weight). We’d have to eat it by the spoonful to get anything like a meaningful amount of minerals.

The second sea salt claim, that it tastes better, is something you can test for yourself. And should, if you’re planning to pay $9 an ounce.

Set a few salts out in dishes, and taste them, blindfolded. (Don’t skip the blindfold; we humans are incapable of factoring out our prejudices if we know which is which.) You’ll find that every single one of them is very, very salty, but you may also find some slight differences in flavor. There may be a distinctive aftertaste to one or two. There may be a detectable mineral tang in another. You may like or dislike those differences, but you can be sure they will be undetectable in any dish that contains those salts, if they’re mixed or cooked or baked in. It’s when salt is sprinkled on top at the very end that the differences can matter. Texture, particularly, comes into play. If you’re going for crunch, Morton won’t do. You might like the big crystals of kosher salt, or the fine flakes of Maldon, or the graininess of a clumpy sea salt.

The only rule of salt is to buy the salt that you like at the price that you like. But, if you’re willing to pay $9 an ounce, let’s talk.

Haspel, a freelance writer, blogs at www.starvingofftheland.com . She will join today’s Free Range chat at noon at live.washingtonpost.com.