Types of Handcrafted Soap
While the chemical reaction that creates soap is always the same, different types of soaps can be made by different methods, all still relying upon that basic chemical reaction that occurs (see How is Soap Made for more information on the actual processes used.
Cold Process Soap
Cold process soapmaking is the method most often used by soapmakers who make soap from scratch. It's called "cold" process because no additional heat is added during the soapmaking process, however the process itself does generate heat.
Soaps produced via the cold process method are opaque and usually have a creamy feel to the bar. Without any additives that change the color, the soap ranges from white-white to creamy-tan, depending on the oils used in making the soap.
The feel of the lather varies, also dependent upon the oils used to make the soap. The lather can range from tiny, very slippery, long-lasting bubbles (as with pure olive oil soap), to big, fluffy, short-lived bubbles (as with pure coconut oil soap).
The hardness of the bar is determined by the selection of oils, the amount of water used and how long the soap was dried. Cold process soaps will continue to get harder as they age because additional water evaporates out of the soap.
Most cold process soaps are made with a combination of oils, in a recipe developed by the soapmaker to create a good lather and hard bar, as well as to provide benefits with additional ingredients.
Hot Process Soap
In hot process soapmaking, additional heat is applied to the soap mixture. The chemical reaction is the same, but occurs faster than in cold process soapmaking. Because of the additional heat, the finished soap bar tends to feel smoother to the touch. The hardness of the bar again depends on the selection of oils, amount of water used in the process and length of time allowed for water to evaporate out of the finished bar.
As with cold process soap, the hot process soap is opaque and ranges from white-white to creamy-tan depending on the oils used, although clear soaps can be produced (see "Transparent Soap" below).
The type and quality of the lather and other benefits of the soap are determined by the oils and other ingredients selected to make the soap.
Liquid soap is usually made with the hot process method, The soap ends up liquid because a different type of lye is used (potassium hydroxide instead of sodium hydroxide) and more water is added. Liquid soaps are typically off-white to amber colored, depending on the oils used. Most liquid soaps are clear or mostly clear.
As a side note, most commercial "liquid soap" or "soft soap" is not true soap; it is made with synthetic detergents.
Transparent Soap is made by the hot process method, with some added ingredients and steps in the process to make the soap clear. There are a few highly-skilled handcrafted soapmakers who produce transparent soap from scratch, but a majority of handcrafted transparent soaps on the market are produced from a ready-made soap base.
Glycerin is a by-product of the chemical reaction of the soapmaking process. In commercial soaps, the glycerin is typically removed, purified and then sold for other uses including food, cosmetics, various industrial production and explosive manufacturing. The method for removing the glycerin from soap is complex and requires considerable equipment and skill. As a result, all handcrafted soaps made from scratch retain the glycerin (and all it's beneficial properties) and so are all technically "glycerin soap".
Subsequently, the term "glycerin soap" is somewhat of a misnomer. Most people using the term "glycerin soap" are, in fact, referring to transparent soap.
Ready-Made Soap Bases
Rather than make soap from scratch, some soapmakers choose to purchase ready-made soap bases which are melted down, have color, scent or other ingredients added and are then poured into molds.
The benefit to using a ready-made soap base is that the chemical reaction which produces soap has already occurred, making it easier for the soapmaker to craft elegantly and uniquely shaped and colored soaps. Many of the artistic presentations of handcrafted soap can only be created with a ready-made soap base.
A ready-made soap base may be a "true soap" (made via the chemical reaction referred to above) or could include synthetic detergents as all or a portion of its ingredients.