What is the difference between lye and soda ash

Sodium hydroxide (NaOH), also known as caustic soda or lye, is a highly versatile substance used in a variety of manufacturing processes. Learn more. Lye, or caustic soda, is a mixture of sodium hydroxide and water. when animal fat and cooking ash mixed in water and made lye-based soaps. Caustic soda has the advantage of mixing to a clear solution, but it costs more than soda ash and generates a considerable amount of heat when.