Shaving soap is not much different from ordinary MP soap except for added clay.The clay is there to help the soap give added slip and also helps your skin.
2 teaspoons of clay per pound ,l also add a teaspoon of sweet almond oil but this isn't really necessary.
Make sure you stir the clay well it and that it dissolves.Clay sometimes settles in the bottom of your mold so when the soap has thickened up a little give it a stir.
Hope this helps