• Safety goggles - must be worn.
• Disposable latex or plastic gloves - another must have.
• Heat resistant non-reactive container (I have used mason or jelly jars with success, You can also use 12 oz. paper coffee cups but they must be double cupped as a precaution because the lye will start to break the paper down)
• Lye powder (Click here for source information)
• Cocoa Butter (obtained from soapmaking supply store)
• Lard or Vegetable shortening (from the grocery store baking aisle)
• Hot plate and pan, or a stove to melt the cocoa butter and shortening/lard.
• Water, cool
• Plastic disposable spoon
• Container capable of measuring 2 oz.
• Thermometer - for measuring temperatues up to 212 degrees F (must be stainless steel, glass or plastic) 
• molds - use half pint milk cartons, small plastic or paper cups, paper portioning cups/trays - use your imagination.

Additives:

• Essential oils, such as lavender, lemon, fake apple, etc. (from soapmaking supply store).  You might also use oil based perfumes or perfumed oils sold for air fresheners.  Ground cinnamon works well, too and is cheap.
• Oatmeal for beauty bar, cornmeal for Dad's garage soap, dried lavender, etc. 

Procedure:

1. Safety first.  We are using commercial lye which is a potent caustic agent.  Safety glasses and gloves as well as plenty of adult volunteers supervising is a must.  If lye gets on you flush with fresh water.  Have water for emergency eye wash available.  Be careful, but the project is worth it.
2. Put on safety glasses and gloves. 
3. measure 2 ounces of cool water into a heat resistant container
4.  Add three heaping teaspoons of lye powder and stir until dissolved.
5. CAUTION:  When Lye mixes with water it generates heat through an exothermic reaction.  It can reach temperatures of 200 degrees Fahrenheit.  It also produces a poison gas so keep your nose away from the container and and use adequate ventilation - an open window or a fan will do.
6. Let the lye cool to about 95 degrees F.  You can place the container in a vat of cold water to speed cooling.
7. Melt a mixture of about 50/50 coconut butter and vegetable shortening/lard.  Don't let it get too hot - just hot enough to melt, not too hot to touch.  Measure out about 4 ounces of this into a large plastic cup (like a grande iced latte cup).
8. Let the fat in the cup cool to about 95 degrees F.  You can place the cup in a vat of cold water to speed cooling.  You can also reheat/cool the fat or lye mixtures to obtain the proper temperatures.  Don't fret too much about exactly 95 degrees - it is a rule of thumb.   
9. When the proper temperatures are achieved, pour the lye solution into the cup of melted fat, stirring vigorously.
10. Stir for 10-15 minutes (this is an unbearably long time for kids.  Encourage them to continue, read them the soap science article and soap history facts from this page, blow bubbles,  maybe show an old Bill Nye video or do magic tricks or something).  During the saponification process, the fat and lye will combine to form the soap.  Stirring is necessary to ensure all the molecules are adequately combined.  The molecules need to bump into each other to combine.
11. When the mixture thickens to the consistency of sour cream, it is ready.  At this point, a drop of the soap will remain on the surface for a second or two.  If it never achieves this consistency after 15 minutes of stirring, then proceed anyway - it will harden overnight. 
12. Pour the mixture into molds.  At this point you can add a few drops of essential oil, a spoonful of oatmeal, ar other additives to make special soaps.  You can experiment with different types. 
13. Science Club members can take the soap home at this point.  They will need to keep the soap warm under a towel for 24 hours.
14. After 24 hours, remove the soap from the mold.  Wrap it in paper and let it season for 2 -3 weeks before using.  Use it in the shower or the tub.  It is a high quality soap, though a little bit strong.  For a milder soap, use less lye and plan on stirring a lot longer.   
15. Provide kids with the Soap Science Take Home Sheet - so they know that they must cure the soap before using it.

Cautions and safety info: 

• Tell the kids to keep hands off their skin and faces, if they don't...
• Have a sink nearby or large bucket with water so kids can rinse lye off their hands.
• Keep several bottles of water on hand for an emergency eye wash.
• Thermometers, spoons and containers must be stainless steel, glass or plastic.  Aluminun creates a poison gas in lye.