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Recollections of domestic life. Soap making, Antigo (Wisconsin), 1884. The farmer is pouring water into the ash barrel to make lye; his wife is boiling a kettle of fat. Lye and fat produce soft soap.
Logs of soap made from lye extracted from wood ash.

Lye, also known as NaOH, sodium hydroxide, or caustic soda, is used in making soap. Caustic potash, or potassium hydroxide (KOH), is also called lye and can easily be made at home. It can also be used in the production of biodiesel, although the recipe will have to be adjusted somewhat.

Basic Recipe

  1. from hard wood ash
  2. extraction with soft water; filter it at the same time
  3. boil off water
  4. voila! The whitish powder is mostly potassium hydroxide

From the Household Cyclopedia (1881)

To make saponaceous Lye for washing: boil together in a sufficient quantity of water, 1 gal. of good wood-ashes and 2 or 3 handfuls of fresh-burnt lime. Leave the lixivium at rest till the extraneous matters have been deposited at the bottom, or thrown to the surface to be skimmed off. Then draw off the pure lixivium, add to it oil, to about a thirtieth or fortieth part of its own quantity. The mixture will be a liquor white us milk, capable of frothing like soap-water, and in dilution with water perfectly fit to communicate sufficient whiteness to linen. This liquor may be prepared from wood-ashes of all sorts, and from rancid grease, oil or butter. It is therefore highly worthy the attention of the economist. When the ashes are suspected to be unusually deficient in alkali, a small addition of pulverized potash or soda may be made to the lixivium.


  • to make biodiesel from various oils
  • soapmaking
  • in food, such as for lye rolls and pretzels
  • key ingredient for geopolymers
  • useful for breaking down cell walls as a preliminary step to extracting phytochemicals from plants
  • oven cleaner and drain opener
  • disinfectant
  • removal of hair from animal hides in the tanning process
  • potentially for geopolymer bricks and other construction

Safety considerations

Lye is highly corrosive and needs to be handled with care (remember that scene from Fight Club?). If you get it on your skin, immediately pour plenty of vinegar on it; this will neutralise it.

Lye should be kept in HDPE containers, as it will burn through anything else.

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