I did some research on the basics of cold process soap making, and found that the only ingredients needed to actually make real soap are oil/fat, lye, water. That's it. I was inspired to try it after learning about some colonial ancestors that lived nearby during my latest genealogy kick. So, we have history, science, and math in one fun project!
There are tons of resources for recipes on the web, but after information overload, I decided to focus on the basics, and use the lye conversion chart at Magestic Mountain Sage. This enables you to plug in what oil you are using, in whatever amount, and the conversion program spits out the amount of lye you need to add, along with basic soapmaking directions.
I found the pure NaOH (sodium hydroxide) lye made by Roebic at Lowes. Red Devil is another brand, though some people report not being able to find pure lye (no additives or fragrance, etc.) at the retail store anymore, I had no problem at Lowes. YMMV.
I used 32 oz. canola oil, straight from the Wesson bottle. I measured the lye on my kitchen scale (used a paper plate to hold the granules), and added it to the 10oz. water in a large wide-mouth canning jar, and stirred. I was outside, wearing gloves, eye protection and upwind of the jar to avoid the nasty fumes. It gets really hot when blending, and you let it cool while getting the other items ready.
I heated the canola oil to 125f in a stainless steel pot. When the lye/water mixture had cooled to 125f, I slowly poured it into the oil, and stirred with a plastic slotted spoon to get it combined. At that point, I switched to my immersion blender, and blasted it for about 30 seconds on and off.
The mixture became more opaque and started thickening. By about 15 minutes, I'd reached "trace", a thick custardy texture that supports blobs dropped off the spoon. At that stage, I poured the glop into my "mold", which was a silicone baking dish (9"x9'')
Normally, at this stage, you would leave it to cure for 24-48 hours, then cut it into bars, set it in a dry place and leave it to cure for a few weeks. BLEAH!!
We opted for the quicker oven processing, whereby you preheat the oven to 170f, put your poured soap in, turn the oven off and let it sit for 12-24 hours. The idea is that the saponification process is rushed along a bit more, and you can use the soap right away. Our bars are now cut, and on a rack wrapped lightly in cheesecloth (to keep any stray cat hair off the finished product), and left to dry out and harden up more.
I did take a few bars right away, undried, to use as the base for liquid soap. Simply enough, you grate your soap (I used my food procesor's grating blade, it's like grating mozzarella), measure it, and add double the amount of water to it in a big stainless steel pot on the stove. Heat it up, mix it with the handy immersion blender, let it cool. I stirred in some glycerin, and bottled the liquid in five different recycled soap dispensers we had around the house. (for 3 cups soap shavings, I used 6 cups water, 1 T glycerin, and each dispenser got 5 drops or so of essential oils - peppermint, spearmint, lavender, and tea tree oil respectively - NOT all together in one, blech!).
The kids loved this project, and especially enjoyed suiting up with splash goggles and gloves :-) Stirring was fun, but the blender is even better. I'm hopeful that this will inspire less bathtime battles. Yeah, wish me luck on that.
Soap Making Instructions from Love To Know Crafts
Cold Process - Oven Process from Soapmaker on a Budget
What is Saponification? - Green Mountain Soap Company
Soaps and Soapmaking Theme Page - links to articles, history, etc.