Castor Oil is a light gold oil that is expeller pressed from the bean of the Ricinus Communis, a tropical perennial shrub.
I use about 20% Castor oil in a shampoo bar (the bar will be a little softer than normal but it makes a great shampoo) and for a normal soap, to boost the lather, I use about 5 - 10%.
The chart below shows the approximate percentages of fatty acids present in Castor Oil. As you can see by the high percentage of ricinoleic acid, a soap made using this oil will have a very conditioning, fluff and stable lather. You will also note the absence of hardening fatty acids which will result in an extremely soft bar. Be sure to use it with plenty of hard oils.
This information is provided for reference use only and is not meant to substitute the advice of a licensed health care professional.