RecipeI basically used this recipe, only I made a quarter recipe so that it would fit in an empty soap pump which held about 1 cup of liquid.
* 1 cup distilled water
* 1 ounce bar soap (approx; I grated about 3/4 inch off a 3.5-inch, 5oz bar of Dr. Bronner's Baby Mild Castile Soap)
* 1/4 tsp liquid glycerin
* 1/4 tsp vitamin E oil (I'd like to use pure vitamin E, but I used a CVS product containing palm oil because we had it around the house. no scary chemicals detected in ingredients list)
* 2 drops Sweet Orange essential oil (I wanted to go light on this, but next time, I will use more - this is currently undetectable over the general scent of soap)
Grate the bar soap and add to water. Bring to a boil. Simmer until the soap is fully melted, about 5 minutes (more if you do a bigger recipe). Remove from heat. Add rest of ingredients. Allow to cool. At this point, you will have what amounts to liquid with a few soap bubbles in it. Bottle and let rest overnight. It will turn into a luxurious pearly gel.
EffectivenessI haven't tested it on truly grimy hands, but it seems to work fine for everyday handwashing, and leaves hands feeling soft.
FrugalityDistilled water is $1 per gallon, or 6 cents per cup. (I used distilled water rather than tap because this recipe has no preservative - the usual suspects, vinegar, salt, or baking soda, would dry out the skin.) A bar of castile soap costs $4, or 80 cents per ounce. My $7 bottle of glycerin contains 14 ounces, which comes out to about 2 cents for a quarter teaspoon. We had the vitamin E just lying around and I don't remember how much it cost, so I won't count that (you could easily leave it out). The essential oils were about 5 cents for 2-3 drops; make it 10 cents because I plan to use twice that amount next time.
All that comes out to 98 cents for an 8-ounce bottle of hand soap. This is about half the cost of buying equivalently-sized bottles of CVS brand hand soap or Softsoap, and competitive with buying hand soap refills in bulk.