Cold Process (CP)
Cold process soap is made up of three basic ingredients: water, lye and fats (oils). The lye is mixed with the water and then that solution is mixed with fats. A reaction takes then takes place between the hydrogen, oxygen, sodium and fatty acid molecules. This is called saponification, and the end result is a substance that is made up of five parts soap and one part glycerin. Glycerin—a rich emollient that softens the skin—is retained in handmade soap but in commercial soap it is extracted, leaving behind the hard, drying bars of soap we purchase at stores.
Essential oils, fragrance oils, botanicals, herbs, oatmeal or other additives can be added to the soap. However not all essential oils or fragrance oils (or other additives) always work well in the cold process method. They can react with the lye mixture and do funky things to your soap…from color distortion to separating your oils.
Once the soap is poured, it needs a couple days to harden before it can be removed from the molds. At this time, it is safe to use the soap since saponification is complete. However, cold-process soaps are typically cured and hardened on a drying rack for 2–6 weeks before use. The longer a soap is left to cure the harder the bar becomes and hence the longer the soap will last.
Melt & Pour (M&P)
Melt and Pour is very much what it sounds like. You start with a glycerin soap base that you melt down using a double boiler. Once the soap base is melted you can add color, fragrances and other additives. Then you pour it in your mold. Let it set for a couple hours and as soon as it’s cooled it ready to use.
In general, M&P is around 50% soap and the balance is solvents. It is formulated to withstand re-melting and accept additives.
Just about anything can be added to M&P soap—dried herbs, ground spices, luxury butters (shea or cocoa), cosmetic clays, dried flowers, fragrances and color additives. M&P also allows you to use fancy molds (more easily) and be a bit more creative with shapes and mixing colors.
Hand-milled (also referred to as French-milled) soap is similar to melt and pour in that the soap is melted and color and fragrances are then added to it. The difference though is that rather than starting with a base that is formulated to be remelted, hand-milled soap is made by melting cold-process soap that has been grated and mixed with a small amount of water. This produces a harder, longer lasting bar, with a smoother and more consistent texture than the original cold process soap.
One of the big advantages is that since the chemical reaction involving lye has already taken place (in the initial cold process batch of soap you’ve made), you can freely add all sorts of ingredients to your soaps—cosmetic clay, cornmeal, citrus juice, spices, cocoa butter, essential oils, herbal infusions, teas, vitamin E, aloe, goat’s milk, honey, oatmeal (and the list goes on and on)—without worrying about how they might be affected by the lye. Plus there’s no worrying about curdling, seizure, refusal to trace, or separation. (All headaches I’ve had to deal with in my cold process soap!!)
Besides making lovely soaps, the rebatching process is a way to fix little disasters. If soap has separated in the curing process or the bars have dried crooked for example, the rebatching helps remedy most of these problems. I had a batch trace so quickly on me it basically solidified in my pot before I could pour it. I plan to hand-mill it so that it’s not wasted.