Make Salt Crystals

Crystals can look quite magical when they appear from nowhere in a glass of water. In fact, they form from substances already dissolved in the water. Make your own salt crystal experiment, and learn how it works at the same time.

Steps

Easy Salt Crystals

1. Heat a pan of water. You only need a little water, about ½ cup (120mL). Heat the water until it just begins to bubble.
   • Kids should ask an adult for help handling the hot water.
   • Distilled water gives the best results, but tap water should work fine.
2. Choose your salt. There are many kinds of salts. Each one will grow into a different shape of crystal. Try these and see what happens:
   • Table salt take a few days to grow. "Iodized" salt won't work as well, but will still form crystals.
   • Epsom salt grows into smaller, needle-like crystals, but grows more quickly than table salt. Buy it at a pharmacy.
   • Alum grow quickly, sometimes making visible crystals within a few hours. Find it in the spice section of a grocery store.
3. Stir in as much salt as you can. Take the pan off the heat. Pour in about ¼–½ cup (60–120mL) of your salt and stir until the water is clear. If you don't see any salt grains in the water, stir in another spoonful. Keep stirring in more salt until you see salt grains that won't dissolve when you stir.
   • You've just made a supersaturated solution. This means the solution (the liquid) contains more salt than water can usually hold.
4. Pour the water into a clean jar. Carefully pour the hot water into a jar or another clear, heat-safe container. This should be as clean as possible, so nothing interferes with the crystal growth.
   • Pour slowly and stop before the salt grains fall into the jar. If there are undissolved salt grains in the jar, the crystals might grow around those grains instead of your string.
5. Add food coloring (optional). A couple drops of food coloring will change the color of your crystals. It might make the crystals smaller or more lumpy as well, but usually not by much.
6. Tie a string around a pencil. The pencil should be long enough to lie across the top of the jar. You can use a popsicle stick or small stick instead.
   • The tiny grooves and rough edges of the string provide a place for salt to latch on and grow. A fishing line won't work, since it's too smooth.
7. Cut the string the correct size to dangle in the water. Only the part of the string underneath the water will grow crystals. Cut it short enough to avoid touching the base of the jar, or the crystals might end up lumpy and small.
8. Balance the pencil on top of the glass jar. The string should hang inside the jar, extending into the water. If the pencil won't stay still, tape it against the jar.
   • Try not to have the string touch the side of the jar. This can make smaller, lumpier crystals grow against the side.
9. Move the jar to a safe place. Keep the container where animals and young children can't get to it. Here are some tips for choosing a location:
   • To grow a lumpy mass of crystals quickly, keep the jar in the sun and/or keep a fan blowing near it on the lowest setting. These crystals may stop growing at a fairly small size.
   • If you want a single, large crystal instead of a clump of crystals, keep the jar in a cool, shaded place. Keep it on a Styrofoam pad or similar material to absorb vibrations. (There's still a good chance you'll end up with a clump, but there should be larger individual crystals within it.)
   • Epsom salt (and a few less common salts) will grow faster in the refrigerator instead of the sun.
10. Wait for crystals to form. Check back regularly to see if salt crystals have grown on the string. Epsom salt or alum crystals can start growing within a few hours, but might take a couple days. Table salt usually takes a day or two to get started, and sometimes up to a week. Once you see little crystals on the string, those will usually keep growing bigger and bigger over the next couple weeks.
    • When the water cools, it has way more salt than cold water can normally hold. This makes it very unstable, so the dissolved salt will leave the water and grab onto the string if it gets a tiny push. As the water evaporates, the salt stays behind, making it even more unstable and encouraging the crystal to grow.

Growing a Single, Large Crystal

1. Grow a cupful of salt crystals. Follow the instructions for the easy method, but use distilled water and do not use a string or pencil. Just leave the salt water in the container. Over the next few days, a layer of small crystals will grow over the base of the container.
   • Use a flat, shallow, wide container instead of a jar. This makes it easy to get a single crystal that hasn't merged with any others.
   • Epsom salts do not work well for this method. Try alum or table salt instead, or see variations below for more ideas.
2. Choose a seed crystal. Once the crystals are ready, pour out the liquid and look at the crystals. Pick them up and examine them with a pair of tweezers. Select a "seed crystal" that will form the core of your new, larger one. Look for crystals that fit this description (from most to least important):
   • Choose a lone crystal, not in contact with any others.
   • Choose a crystal with flat, even surfaces and straight edges.
   • Choose a large crystal (at least the size of a pea).
   • Ideally, find several crystals and set each one up in a separate jar as described below. Crystals often dissolve or fail to grow, so having backups is a good idea.
3. Attach fishing line or smooth wire. Super glue this to one side of the crystal, or tie it around the crystal.
   • Do not use string or rough wire. You need a smooth surface so the crystals can't grow on the string instead of the crystal.
4. Create a new solution. Select distilled water and the same type of salt. This time, warm the water only slightly above room temperature. The goal is to make a perfectly saturated solution. An under-saturated solution may dissolve your crystal, while an over-saturated solution will cover the crystal in salt grains and cause a lumpy mass to grow.
   • There are several faster ways to solve this problem, but they are more difficult and may require some knowledge of chemistry.
5. Add the crystal and solution to a clean container. Clean a jar, then rinse thoroughly with distilled water. Pour the new solution into this jar, then hang the crystal into the center. Store it as follows:
   • Place the jar in a cool, dark location, such as in a low cupboard.
   • Keep it on a Styrofoam pad or other material that absorbs vibration.
   • Keep a coffee filter, paper, or thin cloth over the jar to block dust. Do not use an airtight seal.
6. Check on the crystal regularly. The crystal will grow more slowly this time, since a little water will need to evaporate before the salt grains are forced to attach to the crystal. If everything works out, the crystal will keep the same shape as it grows. You can take it out whenever you like, but it will most likely keep growing for several weeks.
   • About every two weeks, pour the solution through a coffee filter to remove impurities.
   • This is a difficult process. Even experienced crystal growers sometimes have a crystal dissolve or become lumpy. If you have a perfect seed crystal, you might want to test a worse seed crystal first to make sure the solution works out.
7. Protect the finished crystal with nail polish. Once your crystal is large enough, remove it from the solution and dry it. Brush a coat or clear nail polish onto all sides to prevent it wearing apart over time.

Variations

1. Try different substances. There are many substances that will crystallize using the techniques above. You can buy many of them from chemical supply stores. Here are a few options:
   • Copper sulfate for blue crystals
   • Chrome alum for purple crystals
   • Copper acetate monohydrate for dark, blue-green crystals
   • Warning: These chemicals may cause harm when inhaled, ingested, or handled with bare hands. Read the safety information on the label and do not allow children to handle them unsupervised.
2. Make a snowflake. Tie several pipe cleaners or rough wires together in a star shape. Lower these into your salt solution, and watch small crystals coat the star and turn it into a sparkling snowflake.
3. Create a crystal garden. Instead of making a single crystal, why not create a cupful? Make your salt solution, then pour over cut up sponges or charcoal briquettes in the base of the container. Stir in a little vinegar, and watch crystal formations grow overnight.
   • Pour enough to saturate the sponges without submerging them.
   • To make different colors of crystals, add a drop of food coloring to each sponge.

Tips

• Dust in the water can cause smaller or lumpier crystals. Put a mesh or paper towel over the jar to stop it falling in. These materials will still allow water to evaporate, which speeds up crystal growth.

Warnings

• Wash your hands after handling Epsom salt or alum. They are generally safe, but can irritate skin. Do not eat them.

Things You'll Need

• Jar
• Water (distilled or deionized water recommended)
• Table salt, Epsom salt, or alum
• String
• Pencil
• Food coloring (optional)
• Saucepan
• Stirring spoon

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