Ash soap is made from lye derived from hardwood ash. Once you concentrate the lye water, you can turn it into soap by cooking it with fat. Traditional colonial recipes used animal fat, but you can use other types of fat too. Because of the unique type of lye used to make it, ash soap does not produce much lather. It is also much softer than other types of soap. This does not make it any less effective than other types of soap, however!