So this started out as a hot-process potassium hydroxide (KOH) soap project. I don't usually do either, as KOH is more expensive alkali than NaOH (sodium hydroxide lye) and cold process is less work. While I have not changed this opinion, I think this particular recipe is worth the trouble.
I wanted this soap to be concentrated but easy to dissolve. It was to be a dishwasher, laundry and household cleaning gel, as well as the base for an insecticidal/fungicidal soap for the garden and houseplants. Since potassium is a plant nutrient and excess sodium can harm them, KOH was the optimal choice for a base.
The usual personal safety gear (not shown):
Gloves - latex, vinyl, nitrile are all fine
Closed-toe shoes, long sleeves, sensible clothing. It isn't like the scene in Fight Club, but you still want to protect your skin.
Electric drill. If yours is cordless, fully-charged extra batteries are not a bad idea.
Paint mixer. The kind that goes on a drill.
The following items should be kept for soapmaking and not used for food. They should also be made of inert materials: glass, steel, enamel and silicone are good; aluminum and many plastics are not.
Large pot. A large crock pot is better but I didn't have one big enough. I don't think there is one big enough.
Funnel (not shown)
Bucket (not shown)
Sturdy stirring implement. Mine is not shown because the soap won. The spoon was not sturdy and went to spoon heaven.
Thermometer registering the 90 - 180 F range. Two makes things even easier.
A large straight steel spatula is nice but not essential
Small crock pot (not shown)
1520 g KOH
400 g vegetable glycerin
4210 g water
180 g used grapeseed oil
6700 g used peanut oil
Procedure (sorry for the lack of action photos but I did it before I thought of posting the project):
While I am fussy about the oils I use for bath soap and shampoo, used peanut oil seemed just fine for this. I don't fry much, so I used some that was posted for free on Craigslist by a family who fried a turkey at Thanksgiving. It had been sitting in my garage since then and it was time to free up valuable space for other crafty items. My contact confirmed at the time that it was just peanut oil. If you are saving your own, make sure you know what kind of oil it is and how much you have of each if there are several kinds. Avoid fast food and other sketchy sources as some use hydrogenated shortening or blends that can throw off the calculations.
Filter out any particles in the oil. I like to do this before storing but the turkey oil was unfiltered when I got it, which is apparent from the photo. Those black spots are harmless food bits, not mold, and strain out easily.
Weigh your oils. Everything is by weight and metric makes conversions infinitely easier.
Use an online lye calculator that has values for KOH. The discount for liquid soap is usually -10% to 3% in comparison to 5%+ for NaOH cold process soaps.
The water calculation is usually about three times the KOH mass. Since I wanted this to be a fairly stiff gel and peanut oil does not usually produce a very hard cold-process bar, I replaced some of the water with glycerin. These two liquids should be mixed together in the beaker before adding the KOH (and remember to always add the alkali to the liquid, NEVER add liquid to the alkali!). Once the solution is mixed up thoroughly, monitor the temperature. As it cools, heat the oils in the large pot. The goal is to have both at about 140 - 150 F before mixing.
When they are about equalized, mix the KOH solution into the oils and begin mixing with the paint blender. This is the exhausting part, so the electric drill is the way to go. Put the pot on the stove on the lowest flame possible, trying to keep the mixture at about 150 F. It will be exothermic like CP but needs extra heat because you are driving the reaction toward immediate completion rather than allowing for the initial burst before the trace and letting the last bit to occur in the incubation/evaporation period.
It took an hour and a half of frequent stirring and constant low heat for the reaction to be visible. It didn't trace in the CP way so much as go straight to applesauce. Another three hours of intermittent attention and it was thick and translucent. I turned off the burner and let it cool overnight.
The result was a much more solid soap paste than I had anticipated. It was also very concentrated and surprisingly moisturizing to the skin. It came out at pH 8 - 8.5 on litmus paper, which is very mild. The smell, while neither attractive nor repulsive (and nothing very much like peanuts or turkey), was faint enough to be covered by a small amount of essential oil. The cooking pushes the reaction so that it doesn't need the curing time of CP soap, so it was ready to use immediately. I carved it out of the pot in chunks and put it into a covered bucket for storage.
It dissolves easily in warm water and can be diluted to 25% concentration for rich, lathery hand soap. Trials in the dishwasher produced super clean dishes with about half of the detergent compartment filled with paste. Laundry was also a success using about two tablespoons per load.
To make an insecticidal garden soap, take enough concentrate to fill your crock pot 2/3 full. Melt it with as little water as possible, mashing with the masher and spatuling with the spatula to break up the chunks. When it is completely molten, mix in about a teaspoon of neem oil for every two cups of soap. Turn it out into a wide-mouthed storage container and allow to cool.
To use, add a level tablespoon of neem soap to a liter of warm water and mix well in a garden mister. To supercharge it you can add a crushed garlic clove or two and strain out the particles before putting it in the sprayer, but it isn't usually necessary. Allow to cool to room temperature and spray plants well. Neem is non toxic to humans, pets and honeybees and has been used for many purposes for centuries. It and natural soap are generally regarded as acceptable by authorities on organic gardening. Since potassium is a beneficial nutrient for plants, it also counts as foliar feeding every time you spritz them!
A test of 750 mg concentrate melted with 100 g 80 proof vodka in the crock pot (not an open flame unless you enjoy soap flambe) produced a soft transparent soap with a warm honey color. I'm not enough a fan of transparent soap to motivate me to do it from scratch just for the prettiness, but making it from the concentrate is simple enough.
As a bonus, this is a pretty fun sculptural material. Since it is not caustic it can be worked immediately while it is warm and soft - I spent all afternoon playing with it without gloves and my hands weren't dry or flaky at all. It carves well when cool. The cooked paste went through an extruder well. It is lighter than microcrystalline wax and far less stiff. Use vodka rather than water to smooth without generating foam.
Since the oil was free, the cost was really just the price of the potassium hydroxide. Add in a few dollars to cover the neem oil and energy, and it comes out to about $9.50 for a batch of 12 kilos or about 36 cents per pound of paste; diluted to 25% for hand soap, that is less than 9 cents per pound. A load of laundry is about two cents' worth and a dishwasher load comes out to about a penny! Of course, my time does make it priceless </snark>.
I recommend this for other plant lovers and cheap people in general. If you haven't done hot process before, or not in awhile, doing a scaled-back batch first is probably a good idea.