What is the difference?
Great question! We get this question quite a bit, so we want to do our best to provide a clear answer.
Cold-process soap is one of the traditional batch soap processes. It is made from combining fats – in our case, vegetable fats such as sunflower/safflower oil, coconut oil, and palm oil – with an alkali (sodium hydroxide) and water solution. When both the oils and lye are heated to around 95 degrees Fahrenheit they are combined and stirred, allowing for the necessary chemical reaction to take place.
The ratio of fats to lye is important, as a lye-heavy soap (soap containing unreacted lye) will be high on the pH scale and can irritate and burn the skin. Soap without enough lye, on the other hand, will be oily and soft, which will shorten the bar longevity greatly. A homemade soap containing a good ratio of oils and lye will have between 4%-9% extra oil, which is known as “superfatting.” The process of superfatting soap ensures that all the lye is reacted out, allowing for a safe bar, and adds extra oil to the soap, which provides additional moisturizing benefits.
The blend of base oils is also very important, as each oil contributes certain properties to a bar soap. Improper balances result in soaps that are overly drying or too soft. Fortunately, the inquisitive soap maker can develop oil blends that lead to amazing soaps without too much difficulty.
Once the soap is made, it is poured into soap molds and sits for 12-48 hours while the soap reaction continues to take place, and then cools. Finally, the soap molds are cut into individual bars and cured for 3-4 weeks to allow the bar to reach an acceptable bar hardness, which will increase its longevity.
The cold-process method is the perfect solution for people wanting to make soap. It is easy for beginners wanting to experiment with making soap, as it can be done at home with common kitchen tools. Then, because it allows the soap maker to formulate his or her own recipes, it will keep serious soap makers busy for many years to come.
Glycerin Soap (or “Transparent Soap”)
To start, let me first point out that all handmade soap is technically “glycerin soap” because of the naturally forming glycerin that occurs during saponification. In a cold-process soap, glycerin remains in the soap and contributes extra moisturizing properties. (A side note: large soap manufacturers usually extract the extra glycerin, resulting in a more skin-drying bar. The glycerin is then purified, resold, and incorporated into other skin products.)
Now, as for glycerin soap, also known as “transparent soap” – these are the clear bars of soap that you sometimes see with colorful chunks of ribbon and other decorative items inside of them. The process of making glycerin soap starts out like that of cold-process soap, but then goes a couple of steps further. After the fats or oils are saponified, a sugar-alcohol solution (usually sorbitol) is added to the mixture along with extra glycerin. The alcohol solution helps maintain transparency, and the glycerin adds moisturizing properties (because the alcohol is drying). Many people are surprised to find that glycerin soap is not always transparent. Sometimes, to make glycerin soap that looks more like traditional soap or cold-process soap, or simply for decorative purposes, people make glycerin soap that is opaque. To accomplish this, they add titanium dioxide to their otherwise transparent glycerin soap to whiten it.
Now, maybe you’re thinking, “What about that melt and pour soap?” Melt and pour soap is transparent or opaque glycerin soap, usually sold in blocks. Home crafters simply melt portions of the blocks, add scent and color, and pour it into molds. When the soap cools, the soap is ready. It provides an easy way to create homemade-looking soaps in decorative shapes or with decorative objects in them. Melt and pour, however, is not soap making, because the crafter doesn’t really make the soap. He/she does not create the soap from scratch and has no control over which ingredients go into the soap base. However, this type of soap is a safe and great way to get creative with soap, such as making soaps that look like seashells or cupcakes. Also, because the process is so simple, and because no lye is involved, it is a great type of home crafting to do with children.
One more clarification about glycerin soap, including melt and pour. Many people mistakenly believe that this soap is made without lye. That is not true. All soap, regardless of its type, is made from a chemical reaction between fats or oils and lye.
Which One Should I Go With?
Looking at it from a soap making standpoint, cold-process soap is a much easier process and produces a great bar of soap. The downside, obviously, is that only opaque colors can be achieved, and fancy shapes are generally not possible. Glycerin soap can be made at home, but it is harder to accomplish and requires more practice. It can also be a little more dangerous because of the high-percentage of heated alcohol required in the process. The melt and pour method is not really soap making, but it can be a fun process for people wanting an easy home hobby.
Looking at it from a consumer standpoint, both glycerin and cold-process soap contain moisturizing properties and can have beautiful coloring and scent. However, with the addition of alcohol, glycerin soap (including melt and pour) tends to be more drying on the skin. Your best bet is to give both types of soap a try to find out which method you enjoy more and which soap your skin likes best.