Let's talk a bit about how soaps are made, and then in another post, I'll talk about the decisions I make when deciding what goes into my soaps.
According to Wikipedia, soap is "
a salt of a fatty acid...
obtained by treating vegetable or animal oils and fats with a strongly alkaline solution." Whereas a detergent is
"a surfactant or a mixture of surfactants with "cleaning properties"... [consisting of] alkylbenzenesulfonates, a family of compounds that are similar to soap." They also tend to be concentrated, which means they have to be diluted in water prior to use, as in laundry detergent and dish-washing liquid.
So, to make soap "from scratch", you add fat(fat here includes oils and butters too) and a saponification agent, usually an alkali, such as caustic soda (lye) together. Really, just like Wikipedia says. But there are variations in the process, some of which include:
a) the cold-process method (CP).
b) the hot-process method(HP).
Initially there is no difference between making CP and HP soap. You add caustic soda to water, and melt the oils and butters separately. Once both parts are roughly around 40-50 degrees Celcius, you blend them. A stick blender makes things go a lot faster than simply stirring by hand, as the mixture will thicken after a few minutes, resulting in a thick gooey "batter" with little or no visible oil or fat globules on the surface. This stage is called 'trace'. At this point, you can add colouring and scents before pouring it in the mould and leave it to set for 24-48 hours. Unless you're using individual moulds, the soap sets in a block, which has to be cut into grab-friendly sizes and aired for about 4 weeks or longer. This results in CP soap, which is what I do.
Apparently in the old days, people saved ashes from burnt wood to get lye - but you'd have to press water through a lot of ashes, and the strength of the resulting alkali was hard to control which makes for variable soap... There are soapers who do this, and frankly, after seeing pictures of them valiantly trying, I decided that it's not something I really want to bother with. Especially since I have a easy access to pure caustic soda in various stores here in Sweden.
Caustic soda is also known by other names: Sodium hydroxide and/or lye. Yes, the same stuff that you pour down sinks to clear it. Yes, it burns if you get in on your skin. And yes, unless your soap contains too much of it, the resulting soap made with it is safe to use since the lye is used up during the saponification process. You cannot make soap without an alkali, period. I shall discuss the brands I use to make my soaps in a later post on ingredients.
HP soap is something that I haven't tried per se, because instead of the 2-3 hours it takes to make CP soap (I'm a slow worker), it will take at least 6 or so hours. This is how it's done: once the mix has reached trace, slow-cook the goo for at least 4 hours in a low-temperature oven or slow-cooker. Then, towards the final stages of cooking time, scents and additives are added before it too is poured into a mould, then left to set and cut. So far not much difference, right? But there is. The heating accelerates the saponification process, so in fact, the soap is ready to use as soon as it is poured in the mould. However, since the soap still has quite a high moisture content, it still needs to be aired for at least 2 weeks before it will make a longer-lasting bar.
With the CP method, the long curing time is necessary to ensure that all the lye is slowly saponified. This means that if you try to use the soap after 48 hours, it might give you a negative reaction instead. Also, the soap will probably disintegrate almost immediately. (I suspect this is what happened to me when I first tried Lush's soap.)
Sometimes, when my CP soaps have not turned out as well as I hoped, I have done a rebatch. This means, I shred the soap and cook it on my slow cooker with a small amount of water, just as if I was doing HP soap. While the resulting soap is serviceable, they invariably turn dark, and getting the goo in the mould is like fighting with taffy. On the upside, it does make cleaning up in the sink easier, since the soap is ready to use! With some iffy material, such as real tar soap (as opposed to tar-scented), the only way to ensure that the tar is fully incorporated in the soap "batter" is to slow cook it.
The fat-to-lye solution ratio is extremely important in order to make good usable soap; most soapers use a 2,5-2,8: 1 water to lye ratio. I always run my recipes by
SoapCalc, so I can tweak my recipes before I start "cooking". The various oils and fats have interesting properties that SoapCalc does not mention, so getting to know the ingredients is as important and getting the fat, lye and water proportions right. For example: although it is possible to make soap with, say, only olive oil and lye solution, for the small-scale soap maker, trying to get it to trace might take a frustratingly long time, even with a stick blender.
Some Things I've Learnt About Making Soap.
Making a soap with too much coconut butter/oil (that is, over 20% of total fats and oils) will result in a very harsh cleansing bar normally, but you can counter this buy making salt bars. Tried and tested: 40% coconut butter, plus seasalt (also at 40% of total fats) makes an excellent exfoliating bar without drying out skin. (More on salt bars later).
Having 10% of castor oil in your total fats makes for more suds. Handmade soap is not as bubbly as commercial soap. Most people equate suds with better cleansing power, even though that's not true. Other soapers (such as myself) use denatured beer to get more suds in the soap. It is important to boil away any alcohol in liquids used, as even small amounts can cause an unpleasant mess of volcanic proportions once lye is added to it.
Soaps made with tallow (or butter or ghee) tend to have a certain "tallowate" smell (the underlying scent in Lux soaps for example), but also make for a harder, longer lasting bar. Using strong scents or essential oils should mask any unpleasantness. Tbh it is a personal thing - some people hardly notice it, but others, like myself, dislike the tallowate smell. Rendering your own tallow is a cost-effective way of getting good soap-making fat, although if you're chums with the local butcher, you might be able to get some for free. (And the leftover gristle can be fed to the birds.)
Some additives do strange things to soap! Honey and ground cinnamon tend to make soap softer, and the soap may not even harden after 48 hours in the mould. Adding coffee grounds does not impart any coffee smell to the resulting soap, and the grounds can make for a surprisingly harsh exfolliant. Sprirulina gives a lovely initial green colour to soap, but fades over time especially if exposed to light.
Speaking of additives - if you stick to natural colours, then your choices will be severely limited to mostly yellows, browns and reds.There are various clays that can impart other colours to your soap, but they will in turn be affected by your choice of oils. Herbs and natural dyes have been used in soaps, but some (like paprika) can cause an allergic reaction in a few individuals; and indigo if not used carefully can make a "bleedy" soap (and can sometimes turn grey instead of the expected blue). Some soapers use mica powders (although the mica is a straight-out-of-nature product, the dyes are probably man-made), or liquid dyes - you can almost any colour soap this way.
Scenting soap can be a tricky business (and may lead you to yet another hobby). Some essential oils (and fragrance oils) tend to "disappear" in the resulting soap; most of the time, the scent fades after a few months too, although some, like Patchouli, persist for a much longer time. There are loads of sites sharing essential oil flavour recipes, but try to mix your scents ahead of time. Letting a new mix sit for even a few hours may change the overall flavour and may differ slightly from how it smelled when freshly concocted. Also, using EDT in soap: do not expect your soap to smell exactly as your perfume does, it won't. It might still result in a nice-smelling soap, though.
Other Soaps
Some soapers make liquid soaps too. Instead of caustic soda, potassium hydroxide is used - and yes, the pre-soap goo is cooked. Sometime in future, when I've felt that I've researched the matter a little more, I will have a go at it. For now, making good CP-soap is my main priority.
Other soapers proudly claim that their soaps are chemical-free. This is not entirely true, since once fat is added to an alkali, the resulting chemical reaction (ie, saponification) is exactly what is needed to make soap. What they probably mean to say is that there are no chemical detergents in their soap.
Some craft stores, such as Panduro, sell a melt-and-pour kit, usually a glycerin-based clear soap, and it is made as the name implies. You can make some pretty patterns with those, and apparently it is easier to scent. But, just like tallowate, unless it's clearly stated, the glycerin could come from any animal source, since it's a naturally occuring compound in fat. But honestly I don't think making CP soap is really much more taxing, and it allows for greater control in terms of ingredients.