How to Make Caustic Lye from Wood Ash

Mar 20


Catalan Gardener

Catalan Gardener

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If you are interested in making soap at home you will need to source caustic lye. You can either buy caustic soda or make your own caustic lye from wood ash. Here is how...


If you enjoy making soap at home you will probably be using caustic soda bought from a store.  Did you know you could make your own caustic or lye using just wood ash and water?  Bought caustic soda is usually sodium hydroxide but lye made at home will be caustic potash or potassium hydroxide.

It is similarly corrosive,How to Make Caustic Lye from Wood Ash Articles so make sure you keep well covered when making or using homemade lye.  But it is less damaging to make as you can do it on a small scale at home without the need for the transport and chemicals associated with any store bought item.

Also its fun to find ways to use up 'waste products' at home.  Wood ash can build up so why not use some for your homemade soap?

Lye from wood ash will produce a soft or liquid soap unless salt is incorporated into the soap recipe.  But that means it is particularly good for making shampoo and hand wash.

To make lye on a small scale you will need:

  • An old plastic bucket and a larger bucket which can hold the first one.
  • Some ash from burning hard-wood.
  • Some water (preferably rain water).
  • A hand-full of straw.

How to make lye on a small scale:

  • Make a few small drainage holes in the smaller bucket.
  • Put the small bucket into the larger one (to collect the lye water).
  • Put a hand-full of straw over the holes.
  • Fill the bucket 1/3 full with wood ash.
  • Cover with rain water.
  • As the rain water filters through into the outer bucket put it back over the wood ash to concentrate the components it leaches from the ash.
  • Repeat this recycling of the rainwater at least three times over three days.
  • The resulting liquid is lye water.

Testing the Strength of the Lye Water:

  • If a fresh egg floats near the surface with a little lye water above it, the water is the correct strength for making soap.
  • If a fresh egg sinks the lye water is not strong enough and should be passed through the wood ash again.
  • If a fresh egg bobs right on top of the surface the lye is too strong and should be diluted with a little water.
  • A chicken feather will be dissolved by caustic lye at the correct (or higher) concentration.

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