In 18th century America, women stored leftover cooking fats all year in preparation for a yearly soapmaking day.
Solid fats were rendered, then boiled and strained to remove hair and dirt.
Lye was made from hardwood ashes collected from fireplaces.
Rainwater was leached through the ashes and a fresh egg determined the strength of the lye solution. If the egg floated, the lye was too strong, but if it sank slowly the lye was deemed to be the correct strength.
The lye and fats were then stirred together.
Soapmaking was an inexact science, resulting in a soap that may have been soft, hard or harsh.
Whatever the result, it had to suffice until soapmaking day the following year.
Some hundred years or more later, entrepreneurs visited households and bought fat from the households, then made soap and sold it back to the women in large blocks.
Soapmakers also often manufactured candles, as both candles and soap were both made with tallow.