There are hundreds of videos online but I found Everyday Elly’s ones (for sourdough and soap) particularly helpful for general information about soapmaking, and how to calculate quantities, store and cure soap, etc. Here is a link to her YouTube channel: Elly’s Everyday.
Soap made from pure olive oil is called Jabón de Castilla or Castile Soap. Years ago, when we lived in the Sacromonte area of Granada, Consuelo our neighbour would sit in the street outside her house stirring a large vat of leftover oil mixed with caustic soda. Any oil would do she told me and it would make a pure soap that you could use on your skin or clothes.
The second time, I made soap I used the proportions suggested in Elly’s Everyday for Castile Soap:
600g olive oil
79g caustic soda
The important thing is to add the LYE to the water and wear safety goggles, mask and gloves while making the soap.
The total weight of the soap made was 788g and this was enough for 7.8 bars of soap made in the silicone moulds.
The percentages for each ingredient are:
76.14% olive oil
10.03% caustic soda
I have calculated that each mould holds 105g so the quantities for one bar would be:
80g olive oil
10.5g caustic soda
The quantities for 4 bars would be:
320g olive oil
42g caustic soda
The first time I made soap with this method, I placed boards below and on top of the mould and wrapped it all up in a large towel. This supposedly helps the saponification process and ensures that the bars saponify evenly.
I took the bars out of the moulds on the morning of the third day after I had made it. They were all OK except for one so in the future, I will remove them from their moulds after 3 days.