Castor Oil

Castor oil is a vegitable oil pressed from the castor bean. Its a colorless pale liquid oil with possibly a very light yellow color, not quite completly clear. Castor oil is a very thick slighty sticky oil with a very distinct odor and taste. Historically Castor Oil has been used in the past as a laxative. Although used in traditional medicine to induce labor in pregnant women, there is no clinical evidence to sudgest that castor oil is effective for dilating the cervix or inducing labor.
Castor oil has the most abundant source of Ricinoleic Acid, an 18-chain monounsaturated fatty acid.

Castor Oil as a source of Ricinoleic Acid

As noted above Castor Oil is an abundant source of Ricinoleic Acid. Castor Oil is roughly 90% Ricinoleic Acid when it comes to its fatty acid content with smaller amounts of Oleic Acid(~5%), and Linoeic Acid(<4%) with trace ammounts of other fatty acids. Ricinoleic acid is unuaually more polar than most fatty acids thuse making it more water souluable, this is due to it having a hydroxyl functional group on the 12th carbon atom.

Castor Oils affect on Soap

Castor oil is generally used to add extra bubbles to a bar of soap without it being too drying or adding etra hardness to the bar. Since Castor oil is around 90% Ricinoleic Acid it is basically the oil to use if you want soap to gain some of the properties from this fatty acid. In cold-process soap it adds extra lather to the finished product and is also very conditioning to skin and hair. Castor oil is a very thick yet still liquid at room temperature oil. This can help with giving soap a longer time to trace allowing for very interesting swrils or other patternd to be made with the soap as it wont harden as fast as if a large quantity of Coconut Oil or Tallow were added.

How I use Castor Oil

When I make cold Process Soap in almost every recipe i use soamewhere between 5-10% Castor Oil. With Castor Oil a little goes a long way and ive noticed a much lrger lather in bars where replaced a part(about 5%) of my Olive Oil or Safflower Oil with Castor Oil.

Ive Also found that a combination of Argan Oil and Castor oil making up the prodominant part of the base oils in a beard oil renders a really nice result that is conditioning and not overly greasy. Castor Oil is very thick and dosent feely very oily or greasy, perhapse its because in addition to being the only oil in nature to contain more than trace ammounts of Ricinoleic Acid which is a hydroxy acid aswell as a Omega-9 fatty acid.

Recipe Examples

Here is a basic recipe that ive used in the past that had castor oil in it.

Total Oils used                                         Lye solution

500g total recipe or 17.6 oz                        200g water or 7oz

100g Coconut oil or 3.5 oz                          68g of Sodium Hydroxide or 2.4 oz

200g olive oil or 7oz

175g palm oil or 6.2 oz

25g castor oil or 0.9 oz

I would recommend using grams when measuring out everything because being off with the ammount of Lye used by one tenth of a gram can have drastic changes on how conditioning the final bar of soap will be.

Conclusion

Castor oil is a very unique oil with properties much different than Olive Oil or Coconut Oil. Its the only known oil to contain an abundant amount of Ricinoleic Acid which is a hydroxy acid. With just a little bit of Castor oil a lot of extra lather and conditioning properties can be added to soap.