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Shave Soaps)
Shave soaps are not necessarily used for the same purposes as bath or facial soaps--that is, removal of dirt is less important than providing a good shave. There is no agreed-upon definition for what differentiates a shaving soap from other soaps. All soaps could be used to build a lather and lubricate one's face while shaving, but the need for a durable, moist, and lubricating lather leads to customized soaps produced to provide such qualities (qualities not necessarily needed in bath or face soaps). Shave soaps are therefore made to provide moist, low-friction lather that allows razors to glide across the skin's surface without skipping or catching on the skin, two common sources of nicks and irritation. Shave soaps may also contain products intended to soothe the skin or provide antiseptic qualities, as well as fragrances that have no effect on the shave but are pleasing to the user.
Soap Chemistry
Soap is strictly defined as an alkaline salt of a fatty acid, but this definition may not be helpful to most readers. It is first important to distinguish soaps from other cleaning substances such as solvents and detergents. Soap is formed when a strong base (alkaline) is reacted with a fat or oil such as tallow, palm oil, or coconut oil. The base is almost always sodium hydroxide or potassium hydroxide. The hydroxide breaks off a long carbon chain from the lipid molecule, resulting in a soap molecule, and glycerin. The relative proportion of glycerin depends on the type of fat or oil. Petroleum (mineral) oil is not a lipid and is not saponifiable. Not all lipids are actually saponifiable either; for instance, steroids (such as cholesterol) cannot be saponified.
Soap can also be manufactured by pre-breaking the lipid (usually a triglyceride) into its glycerine and fatty acid components before reacting the fatty acid with the alkaline hydroxide. If this process is used, the soap reaction is a simple neutralization between an acid -- the fatty acid -- and a base -- the hydroxide. No glycerine is produced in this reaction because it
was removed to produce the fatty acids.
Detergents perform a similar function to soap (they are both "surfactants" and can bind to water on one end and oil on the other end of the molecule) but are most commonly made from petroleum instead of lipids. Detergents do not leave "soap scum" or a "bathtub ring," normally caused by a reaction with iron or minerals in the (hard) water. Some body wash bars are not soap but rather detergent (sodium cocoyl isethionate), so they do not leave soap scum or a bathtub ring.
Bar and Cream Soap
Sodium hydroxide (lye) makes a hard soap. Potassium hydroxide makes a softer or gelatinous soap. These two types are usually mixed to make a shaving cream soap. Sodium lye soaps are hard, and thus shaving soap "pucks" are made from a reaction of sodium lye and lipids. Both types of soap-making reactions produce glycerin. Some soap manufacturers extract the glycerine, by distillation, for resale and use in other products. As glycerine is a product of a soap-making reaction, it is fallacious to refer to a soap as "glycerine-based," since glycerine is not a raw material for making soap, though it can be added to soap. Glycerine (also spelled glycerin) is a clear, viscous liquid that is used as a moisturizer. Its relative expense compared to other moisturizers such as cocoa butter or jojoba oil often makes it cost-effective for soap manufacturers to extract glycerin and replace it with a cheaper alternative in their soaps.
Hard soaps can be made translucent by the addition of alcohol to ground soap particles after the soap process has completed. Glycerine has limited impact on the clarity of a soap. Liquid soaps and some cream soaps are translucent without the addition of alcohol, primarily due to a higher water content in the soap.
Fats, Oils, and Waxes
Most naturally occurring lipids (fats, oils, and some waxes) can be used in the soap making process. One common fat is tallow. Tallow is rendered beef fat (lard is rendered pork fat). Some people may avoid soap made from animal products. Palm oil is chemically very similar to tallow and thus is a common substitute when making all-vegetable soap. Palm oil often imparts a noticeable (possibly described as "off") smell and, as a result, unscented all-vegetable soaps are uncommon.
Each lipid imparts characteristics to the final soap product. Most commercial soap, regardless of brand, color, or properties, is made from "80-20 soap base;" 80% tallow, 20% coconut oil. This base is usually shipped in small nuggets or "noodles", and compressed into bars, along with any additives, at the manufacturer. 80-20 soap base is very hard, a product of its high tallow percentage.
Olive oil is another common soap component. Its relative expense compared to beef tallow and coconut oil makes it less common in low-price soaps. Palmolive ("Palm-olive") soap was so named because it was made exclusively from palm and olive oils.
Any excess oils left over after the saponification process may eventually oxidize and go rancid. As such, preservatives such as BHT are often added to tallow and other oils or fats to slow this process.
Soap Additives
Many soap makers add products to soap, during the saponification process or afterwards. These products may change the color of soap (titanium dioxide or Yellow #5), add fragrance, increase or decrease the foaming action of the soap (using clays such as bentonite or kaolin, or chemical additives such as sodium laureth sulfate), or, as noted above, change the moisturizing properties of the soap. Some additives may be purely physical, such as pumice, ground oatmeal or pecan shells, or other exfoliating substances.
If the additives are oils and are saponifiable, and are added to the soap during the soap-making process, the additives (or at least the oil component of these products) will be reacted into soap and glycerine. If the additives are not saponifiable, they may be added at any time; if the products are saponifiable but are not added during the saponification process, they may be added during a milling process after the soap has cured and hardened.
Milling Soap
Milling is a process by which soap is forced through a machine with very tight or thin space, usually between two cylinders. In order to evenly distribute soap additives not present during saponification, soap additives may be mixed with soap or added as a coating, and then milled to physically redistribute the additives. Some additives are not totally or evenly dispersed during the first milling process, and thus some soaps are "double milled" or "triple milled" to ensure that the soap is uniform.
By contrast, "hard-milled" soap is soap without water or glycerine. Once the soap and additives are uniformly milled, they are run through a plodder to compress the soap "ribbons" or "noodles" into the shape of a soap bar. The bar is then cut into soap blanks and finally stamped into a finished bar.
Melt-and-Pour Soap
Melt-and-Pour soaps usually contain about 50% soap and the remainder is solvents, additives (often glycerine, as glycerine has a low melting point), or binders. The soap and the additives can provide a good shave, though no known commercial soap manufacturers use melt-and-pour as a base for their shaving soaps. It is possible that references to "glycerine-based" soaps refer to melt-and-pour with large amounts of added glycerine.
See also
