How to make homemade soap with caustic soda

Updated February 21, 2017

Caustic soda is another name for lye, and you can't make soap without it. Unfortunately, it is extremely toxic, and care must be taken not to get the caustic soda on your hands or in your eyes. Set up your soap making area in a well-ventilated room or outdoors. Homemade soap, despite all the warnings, is one of life's simple pleasures. It can be very economical, too.

Line the cake tin with waxed paper. Wear a respirator, eye protection and rubber gloves. Carefully mix the water and caustic soda together in a glass bowl, stirring gently with a spoon. Put a thermometer in it and put it aside.

Stir together the olive oil, coconut oil and grape seed oil. Put another thermometer into the mixture.

Pour the caustic soda mixture into the oil mixture slowly once the temperatures of both containers reach 43 degrees C (110F).

Mix with a hand blender until the soap solution is thick, but still pourable. Add a dash of cinnamon oil at the end, mixing in quickly.

Pour the mixture into the mould and cover with heavy blankets to keep the heat in for 24 hours. Don't allow the blankets to touch the soap, though.

Cut the soap, after it has set, into soap bars by using a guitar string. To make it easier, wrap each end of the guitar string around a chopstick so that it's easier to hold the string when cutting.

Lay some brown paper bags flat in a cool, dry place and place the bars on them. Turn the bars over after two weeks, and they will be ready to use two weeks after turning.


Do not substitute this recipe with any other oil, as it may start a fire. Every oil requires a different amount of caustic soda.

Take care not to inhale the fumes. Keep the caustic soda away from people and animals since it is extremely toxic.

Dedicate utensils and bowls just for soap making. Do not reuse for cooking.

Things You'll Need

  • 22.5 by 30 cm (9 by 12 inches) cake tin
  • Waxed paper
  • Respirator
  • Eye protection
  • Rubber gloves
  • Glass bowl
  • 750 ml (3 cups) purified water
  • 250 ml (1 cup) caustic soda
  • 1 litre (4 cups) non-virgin olive oil
  • 500 ml (2 cups) coconut oil
  • 500 ml (2 cups) grape seed oil
  • 2 Thermometers
  • Hand blender
  • Cinnamon oil
  • Heavy blankets
  • Guitar string
  • 2 Chopsticks
  • Brown paper bags
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About the Author

Katie B. Marsh is a self-published author, article writer, screenwriter, and inventor. After graduating from South Coast College of Court Reporting, she worked as a congressional and freelance court reporter for eight years. She began her writing career in 2005. Her content may be found on,, and She completed her first screenplay in October 2009.