Adding salt to make soap harder

his was my first experiment with medieval soap, that I displayed at Fall 2023 Atlantian Coronation. I took a class on saponification (the soap making chemical process) at Atlantia’s Summer 2023 university and got interested in soap making.

In that class it was mentioned that sodium hydroxide gives hard soap and potassium hydroxide gives soft or liquid soap. But the class also mentioned that passing water though wood ash produces potassium hydroxide. That would suggest that medieval soap was liquid soap, but then I found mention that adding salt (sodium chloride) while making the soap made it harder, so I had to experiment.