Introduction

Growing crystals is a slow and careful process because the crystals grow by adding single layers of molecules.  The crystal shape reflects the basic patterns by which the molecules of the crystal build up.

For example, growing a sugar crystal.  We start with a sugar solution which has as much sugar dissolve in it as possible.  As water evaporates, the sugar solution has too much sugar in it.  Sugar is forced to leave the water solution and become solid again.

Our mission is to coax this sugar to leave the water and go onto our baby (seed) crystal that we have suspended into the water solution.  Thus, as more water evaporates, our seed crystal grows and grows.  If this growth process is slow enough, our crystal will grow one layer at a time and and take on a interesting geometric shape: the crystal's shape reflects the directions of "slowest growth" of the crystal.

This recipe uses the evaporation process.  Water evaporates from a super-saturated solution of dissolved  material.  The process of growing a crystal can be broken down into the following steps:

• Making a saturated solution
  This is the bulked-up solution which, as water evaporates away, forms the crystal.
• Growing seed crystals
  "From tiny acorns, mighty oaks grow."  This saying goes for crystals, too.  Crystals will spontaneously grow from a saturated solution but, in order to control the process, you need to start with a seed.  As the saturated solution evaporates, crystal material deposits on the seed and not haphazardly everywhere else.
• Growing a crystal
  Crystal growing is like meditation.  A calm and steady environment produces healthy crystals.  Any variety of disturbances will lead to imperfection and discord.

Water is a safe and abundant solvent.  Anything that dissolves in water can potentially be used for crystal growth.  Some common materials that can be obtain at stores and pharmacies are:

• Sugar (sugar crystals are also called "rock candy")
• Salt (Sodium Chloride)
• Alum (usually aluminum ammonium sulphate)
• Copper Sulfate
• Rochelle Salt (Potassium Sodium Tartrate)
• Potassium Ferricyanide (don't let the cyanide part fool you.  It's a medicine.)

For this exercise, we will be using common alum because it is easy to obtain, safe to use (it is a medical astringent), and produces clear tetrahedral-shaped crystals.  Also, putting a little chromium sulfate into the saturated solution adds a purple color to the crystals.

Remember the old Warner Bros. cartoons where Tweety Bird shoves a spoon of white powder into Sylvester the Cat's mouth.  Sylvester's mouth puckers up so much he can't eat Tweety Bird.  That powder is alum.

Pretty Crystal Pictures

Click on any of these thumbnails to see some of the home-grown crystals that can be made.
 

Potassium Ferricyanide	Copper Sulfate	Ammonium Alum (Co)	Alum Mixture	Rochelle Salt
small picture	small picture	small picture	small picture	small picture
large picture	large picture	large picture	large picture	large picture

 
 

Making a Saturated Solution

The first step in making crystals involves preparing a water solution that has as much alum dissolved in it as possible.  This is called a saturated solution.

1. Start with a clean jar that can be covered and shaken.  Add water to the jar.
    
2. Add an amount of alum to the water. Shake well and let stand for 30 minutes.
    
3. If there is NO powered alum visible on the bottom of the jar then repeat step 2 until there is.
    
4. Carefully pour off the liquid into another clean jar (without getting any powder into the liquid) and seal this new jar tightly.  This is your saturated solution.

Making Seed Crystals

Find a wide low jar.  Clean it well and pour some of the saturated solution into it.  Cover the low jar with a clean piece of cloth; this will allow the water to evaporate and keep dust from falling into the jar.

Set the jar in a dark area and wait.  Gradually, as the water evaporates, tiny crystals will begin to grow at the bottom of the jar.  Eventually, these crystals will be large enough to work with using your fingers.  Remove these "seed crystals" from the jar.  They will be used to make much larger crystals in the next step.

Sometimes, instead of getting a few seed crystals growing, you get a whole carpet of tiny crystals growing on the bottom of the jar.  This means either the water or the jar was dusty.

Growing Crystals

We are now ready to transform our tiny seeds into full blown crystals.

1. Clean a wide jar and place a wire over it as shown in the figure below.
   
   
2. Fill the jar with saturated solution.
   
   
3. Using thin nylon thread (or fishing line), tie a string to the seed crystal.  You may need to scratch some small grooves into the seed crystal for the string to hold onto the seed.  Avoid fabric threads since tiny seed crystals will form along the lint ends of the thread.  The result will be a gumble of crystals and not a single large crystal.
   
   
4. Suspend the seed crystal into the saturated solution close to the bottom of the jar.  Use a piece of tape to fix the string to the side of the jar.
   
   
5. Cover the top of the jar with clean cloth.  This keeps dust from falling into the jar and allows the water to evaporate out.

Finally, place the jar in a spot out of the sun where the temperature of the air does not change over time.  Gradually, over time, the water in the jar will evaporate.  Solid alum will leave the saturated solution and disposit onto the seed crystal.  The crystal will grow and change shape.  Because the crystal grows faster in some directions and slower in other directions, the crystal doesn't look round like a ball. The crystal's shape is determined by the directions that grow the slowest.

Final Comments and Other Links

There is no end to how large a crystal you can grow.  There is only an end to your patience.

These crystals were grown in a water solution.  Water is actually a part of these crystals: almost like a glue.  If you heat these crystals, the water would be forced out and the crystal would crumbled apart.

What would happen if you tried to grow a crystal in your refrigerator?

What would happen if you added water to the saturated solution while you were growing a crystal?
 

See also:
Udo J.A. Behner's site where he discusses commercial growing of crystals as well as sells kits for growing at home.

Tri-Ess Sciences Inc. is a retail scientific supply which specializes in small quantities of chemicals and lab equipment for students and hobbiests. They sell all the chemicals for crystal growing (Aluminum Potassium sulfate, Chromium Potassium Sulfate, Potassium Sodium Tartrate, Copper Sulfate, etc.) plus a book Crystal & Crystal Growing.

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