How to Grow Salt Crystals at Home

It started because Mia wanted to make "snow."

She'd seen online video of white crystals forming in a jar and had decided, with the certainty of someone who has never checked whether something is actually possible, that we were doing this today.

"We need salt," she announced.

"We have salt."

"A lot of salt."

I looked at the table. I looked at her. I thought about the fact that it was raining, we had nowhere to be, and the kitchen already had that end-of-week feeling.

"Right," I said. "Get the biggest jar we have."

The Setup

Salt crystals are one of those experiments that requires patience in a way that somehow teaches patience without anyone saying the word "patience" once.

Here's what you need: a glass jar (the taller the better), table salt, hot water, a pencil, some string, and a paperclip. That's genuinely it.

We boiled the kettle and poured hot water into the jar (about two-thirds full). Then came the interesting part. Mia added salt, stirred until it dissolved, added more, stirred again. We kept going until the salt stopped dissolving no matter how hard she stirred.

"Why won't it mix anymore?"

"Because the water is full. Saturated. It can't hold any more."

She stared at it. "Water can get full?"

"Of salt, yes."

She found this concerning in a way I couldn't quite read. "Is our drinking water full of something?"

"Not like this, no."

She decided to trust me on that and moved on.

The Waiting Part

We tied the string to the pencil, clipped the paperclip to the bottom as a weight to keep it hanging straight, and rested the pencil across the mouth of the jar so the string dangled into the salty water without touching the sides.

Then we covered the jar loosely with a cloth and put it somewhere it wouldn't be disturbed.

"Now what?" Mia asked.

"Now we wait."

She looked at me.

"It takes a day," I said. "Maybe two."

The Science Bit (Which She Figured Out Herself, Mostly)

The next morning she checked before breakfast. There were tiny white crystals forming on the string, clustered around the paperclip, each one a perfect angular cube.

"They grew," she said, with the tone of someone who had expected this to fail.

We looked at them together. "What do you think happened?"

She thought. "The water... dried up a bit? So now there's too much salt?"

"Exactly. The water evaporates overnight. But the salt can't evaporate. It's stuck. So the water that remains is more than saturated. It needs somewhere to put the extra salt."

"So it puts it on the string."

"It puts it anywhere it can. The string just gives it a place to start."

She picked up the jar and tilted it gently to watch the crystals catch the light. "They're like tiny boxes."

They were, actually. Salt forms cubic crystals, little perfect squares stacked on each other. You can see the geometry if you look closely, which she did, for about four minutes straight, which is an eternity in seven-year-old time.

Day Three

By the third day, the crystals had grown into a small cluster, white and slightly rough to the touch, like something you'd find on a beach. Mia had named them collectively "Gerald."

"Gerald's looking good," she said at breakfast.

He was. The crystals had spread up the string, each one adding to the structure that was already there. It had that quality of looking like something that couldn't possibly have made itself - too geometric, too regular - but it had, from nothing but water and salt and a few days of patience.

"What happens if we put Gerald back in fresh water?" she asked.

I hadn't thought about this. "What do you think?"

"He'd dissolve again."

"Want to try?"

She did, and she was right, and she was quietly triumphant about it in the way children are when a hypothesis turns out to be correct.

What You're Actually Teaching

Salt crystals are a lesson in saturation, the idea that something can reach capacity, hold no more, and start to change form as a result. It's also a lesson in evaporation, in crystal geometry, in how structure emerges from chaos.

But honestly, the thing Mia got wasn't any of that. What she got was the experience of watching something grow slowly over several days and caring whether it worked.

Gerald ended up on the windowsill. He's still there.

Your Turn

You need a jar, table salt, hot water, a pencil, string, and a paperclip.

Make the water as salty as it will possibly go, add salt until no more dissolves no matter how long you stir. Hang your string in. Cover loosely. Leave overnight.

Check in the morning. Then check again.

Try food colouring in the water if you want crystals with colour. Try different shaped containers to see if the shape of the jar changes anything. Try putting two jars side by side in different rooms to see which evaporates faster.

The crystals will come. You just have to let the water get on with it.