In the past most families made their own soap. This was only possible when they had enough ashes from which to make potash or lie (check that). This was usually at the end of the winter hence the term ‘spring cleaning’. It is nothing to do with spring as a season but rather that they were actually able to make soap.
This soap tended to be liquid and the rise of the commercial companies, such as Lever Brothers, was based on these companies being able to make bar soap which lasted for some time.
Soap making is essentially quite easy if you have the right ingredients, and also provides a good moisturising and beauty aid if the glycerine is left in.
There are arguments against modern soaps and detergents due to their chemical components, whether that be colour or fragrance. In the past most soap was coloured by natural or vegetable dyes which of course faded in time on exposure to light.
It was also subject to a relatively short shelf life, perhaps little more than a year. This has not been noticed by UK manufacturers.
The ability to make soap depends upon the unsaponifiables, these are present in better quality food grade oils so refined oils are better for soap making. Basically fats are heated up and then caustic soda is added to the content. It is claimed that this caustic principle disappears very quickly in a properly made soap.
All sorts of other good ingredients can be added in such as essential oils, herbs, anything I suppose which is fat soluble such as herbal oils.