The chemistry of soap - Pure magic
Chemically, soap is an alkaline salt created by mixing a strong base with one or more fatty acids. Alkaline means basic. Two different bases, sodium hydroxide and potassium hydroxide, are used in soap making. When sodium hydroxide is used, the soap becomes solid and when potassium hydroxide is used, the soap becomes more like a jelly, which is what is used in the manufacture of liquid soap. The reason why the two different hydroxides create different textures of soap is that sodium is a harder metal than potassium.
It may sound scary with strong alkaline and corrosive but none of that is left in the soap. The fat and lye are reformatted into two new substances, soap and glycerine.
So what happens when the fatty acids meet the base?
The oil and/or fat is an ester consisting of a triglyceride, which means that there are three fatty acid molecules attached to a glycerol molecule. It is hydrolyzed in the reaction to form glycerol and fatty acid. Hydrolysis is a chemical process that involves the breaking of a bond of a molecule as it reacts with water. To the fatty acid, which is negatively charged and forms an alkaline salt with sodium or potassium ions (depending on the base used). Soap and glycerine are formed.
Different oils give different results
Oils and fats are like the soapmaker's colors on a palette, all of which can be mixed with different beautiful results. To put together a good soap recipe, the soapmaker looks at what fatty acids each desired oil contains and can then form an idea of how the finished soap will be. The fatty acid composition affects the hardness of the soap, how the soap batter is to work with, how the lather will feel and what skin care properties the soap will have. A large part of the art of soapmaking lies in the recipe.
Saponification figures
Depending on the fatty acid composition of an oil, different amounts of sodium hydroxide or potassium hydroxide are needed to reformat the oil into soap and glycerine.
The method of calculating saponification numbers has been around since the 1800s and in the context of soap is new, before a legend goes about a wonderful trick where you simply put a raw egg in the homemade lye and if the egg floated, the lye was strong enough for soap. Soap & Wash recommends counting saponification numbers when making soap.
Ph value in soap
Soap is an alkaline salt. The pH value varies between 8.5-10. Neutral ph is 7 and the skin's is around 5. The fact that the soap is slightly basic is nothing that bothers your skin as long as it is a natural soap, ie has retained its natural moisturizing glycerin, and that it is overfatted. The overfatting and glycerization gives a rapid ph-correlation.
But where does the slightly basic pH value in the soap come from and what controls it? The oil/fat is not water-soluble and therefore has no pH value, but the oil/fat consists mainly of fatty acids, which are acids, so when the soap and glycerine are created, it can be said that the fatty acids tame or neutralize the base, which has a pH value of around 13 in its pure form. The neutralization takes place during the saponification in the hydrolysis where the soap and glycerine are created.
Fact box Glycerine
INCI name: glycerin
Why is it in soap: In artisan soap, it is naturally created during saponification, acts as a fructose and moisturizes the skin. In industrially produced soap, glycerine is added afterwards.
First to clarify; glycerin and glycerol are the same thing and are a moisture-binding substance chemically an alcohol. Glycerine is found naturally in our skin and a little everywhere in nature even in small amounts in oils and fats. In a cold process soap, between 9 and 14% glycerine is naturally created during saponification, which is then bound in the soap. In a hot process soap making method, the glycerine precipitates by itself and is utilized, in good soap it is added again and in a poorer one it is used for other purposes. In the soapmaking method where an already saponified soap mass is pressed, glycerine is added together with fragrance and other additives before the soap mass goes through pressing.
Glycerine is used in many cosmetic products such as creams and makeup to retain moisture and provide the right consistency. Glycerine made by saponification of oils is particularly desirable and of high quality.
Fact box Potassium hydroxide
INCI name: potassium hydroxide
Characteristics: highly corrosive bath easily soluble in water. Comes in the form of flakes or beads.
Property in soap: Creates a soap instead of solid soap.
Potash is sometimes mentioned and is actually called potassium carbonate, the predecessor of potassium hydroxide and what was used in the soap factories from 1600 onwards to make soap.
The reason why sodium hydroxide and potassium hydroxide create different consistencies in the finished soap is that sodium is a harder metal than potassium.
Fact box sodium hydroxide
INCI name: sodium hydroxide
Characteristics: highly corrosive base easily soluble in water. Comes in bead form.
Property in soap: Key ingredient in the manufacture of solid soap. No soap in the sense of real soap can be made without sodium hydroxide. It is important to mention that none of the dangerous corrosive remains in the finished soap.
NaOH is a base that releases hydroxide ions in aqueous solution. It is highly corrosive in both dissolved and undissolved forms. A solution of sodium hydroxide in water is used in soap making. NaOH is produced by electrolysis by passing a current through an aqueous solution of saline, after which the solution is evaporated into a solid form and then purified with alcohol. The process is called the chlor-alkali method. The sodium hydroxide used by Soap & Wash is produced in the lab of a chemical engineering factory in Germany. It is important as a soap maker to ensure the purity of its sodium hydroxide to be able to get a smooth and safe result in manufacturing and a purity of at least 99% is recommended.
Long ago, as early as 3000 BC, the Egyptians produced strong bases very similar to sodium hydroxide and used them in the same way. Soda ash, sodium carbonate, was the most common and it was extracted by preparing ash wood. Even today, you can make your own sodium hydroxide by running water slowly through ash wood. The sodium hydroxide we know today first appeared in 1755 when sodium hydroxide was successfully extracted from sodium carbonate. Before then, no distinction was usually made between the different alkalis, and if one was made, it was potash that was used for soap or mineral potash that was best for solid soap. It is exciting to think about how the soap and soap were in the past and in all likelihood the feeling for the craft was in the hands and the amount of raw materials needed was something you learned from a more experienced. Before that
The same NaOH as made in the lab, only less pure and controlled can be extracted from charred wood through which water is allowed to flow, that's how they made their natirum hydroxide solution in the past.
Lye = sodium hydroxide, soda ash or potassium hydroxide dissolved in water.