Salt and vinegar crystals are easy-to-grow non-toxic crystals that you can grow in a rainbow of colors. This crystal growing project is especially useful for kids or beginners looking for quick and easy crystals.

Materials

1 cup hot water (H)

1/4 cup salt (sodium chloride)

2 teaspoons vinegar (dilute acetic acid)

food coloring (optional)

piece of sponge

shallow dish

Instructions

Stir together the water, salt, and vinegar. Boiling water works best, but it's alright if the water's not quite boiling. Place the piece of sponge on the shallow dish. Pour the mixture over the sponge so that it soaks up the liquid and almost covers the bottom of the dish. If you want colored crystals, you can dot the sponge with food coloring. As the crystals grow, the colors may run together a bit. You can use this to your advantage to make more colors. For example, dotting blue and yellow food coloring near each other can produce blue, green, and yellow crystals. Save the rest of the crystal growing solution in a sealed container. Set the dish in a sunny window or another warm area with good air circulation. You will see crystal growth overnight or within a day. Add more crystal growing solution to replace the liquid that evaporates. Continue growing your crystals as long as you like. The project is non-toxic so when you are done, you can either save your crystals or else throw them away. You can dump leftover crystal solution down the drain and wash the dish as usual. You can keep the crystals and watch them. Over time, the salt will react with water in the air to subtly change the appearance of the crystals.

How the Crystals Grow

Salt dissolves better in hot water than cold water, so as the solution cools the salt wants to come out of solution and crystallize. When you pour the solution over the sponge, this causes the liquid to evaporate. This further concentrates the salt so that it will crystallize. The salt crystals will start to form on undissolved salt or the sponge. Once the crystals start developing, they grow fairly rapidly.

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