First, sorry for the late translation. Those who follow me on Facebook may have seen it, I made homemade soaps this fall (2019) with a friend who does it often and prefers to remain anonymous. The writing of this article made me dust off my notions of CEGEP chemistry. If anyone can help me improve the description of the chemical reactions, I would be delighted! To make homemade soap nowadays, you need:
- One or more fatty substance (lard, olive oil, tallow, almond oil, castor oil, etc.)
- Sodium hydroxide (NaOH)
- Water (H2O)
- Essential oils (essential for perfume only)
- A website to calculate the proportions of ingredients: we used SoapCalc
A few words about saponification
It was important for me to return to the basic science behind the making of soap. This section contains quite difficult chemistry concepts, consider yourself warned. Basic notions in chemistry are required for understanding. You can skip this reading if it seems unintelligible to you. In other words, this section is more difficult to understand than my usual subject matter.
The process that turns NaOH (an alkaline or a basic solution) and fatty substance into soap is called saponification. From a chemical point of view, a fatty substance is a carbon chain (called hydrocarbon in chemistry), Ch3-X(Ch2)-COO-Y(CH2)- CH3, where X and Y represent a number between 2 and 22. This type is called an ester. When a tail ends with an acid group, COOH, the molecule is then called a fatty acid. The purpose of saponification is to transform the carboxylate acid (fatty acid) into the carboxylate ion (soap), in other words to remove a molecule of hydrogen from the carboxyl group of the acid.
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| Chemical description of a fatty acid molecule To transform this fatty acid molecule into an ester, it is ''just'' to replace the hydrogen atom linked to the oxygen atom with a second hydrocarbon chain. |
Saponification is a slow, exothermic reaction, which produces heat. Adding heat to the ingredients will speed up the reaction. Vigorously shaking the mixture also accelerates the reaction.
The chemical saponification reaction takes place in three stages.
In the solution (meaning dissolved in water), NaOH separates into ions: Na + and OH-.
The first step occurs when the OH- group binds to the carboxyl group of the fatty acid ester. An ester is a more stable molecule than a fatty acid, having a carbon chain on both sides of the COO complex.
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The Rs represent the ends of molecules (carbon and hydrogen chains) which do not react during the reaction.
From Wikipedia on Saponification |
The second step occurs when an alcoholate ion (OH-) separates from the new molecule formed in the first step.
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| On the right is a carboxylic acid and a negatively charged alcoholate ion. From Wikipedia on Saponification |
The third step is the only non-reversible step. Is present in the solution of the molecules of each stage. The first two steps transformed an ester into a carboxylic acid. The alcoholate ions (second product of the second reaction) are strong bases which will react with the acid in solution.
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| The carboxylate ion is the active molecule of soap, the alcohol produced is often glycerol which adds to the moisturizing action of soap. From Wikipedia on Saponification |
I'm not going to lie, most of my information on the chemical process leading to saponification comes from a Wikipedia page on Saponification and on this blog dedicated to soap.
I end this section with a more digestible formula for ordinary people which summarizes the saponification reaction.
Base (alkaline medium) + Fat (ester) = Soap (carboxylate ion) + Alcohol (Glycerol)
I end this section with a more digestible formula for ordinary people which summarizes the saponification reaction.
Base (alkaline medium) + Fat (ester) = Soap (carboxylate ion) + Alcohol (Glycerol)
How does soap work?
The soap (ion carboxylate) is formed of two distinct parts: a hydrophilic part (the COO- head is attracted by the water molecules) and a hydrophobic/lipophilic part (the tail formed of carbon chain is repelled by the molecules of water but attracted to fat molecules). The principle is simple: the tails of carboxylate ions surround the fat particles to form a micelle (a fancy word for an aggregated of molecules) and allow the water, attracted by the heads of the molecules, to evacuate the micelles. Bacteria, in the same way, are not killed by soap but trapped in micelles to be then carried away by water.
Whenever soap is used, this chemical attraction reaction between greasy parts (stains) and water occurs.
Myth: a soap only washes well if it bubbles. Actually, the ability to foam is the ability of soap to trap a film of water between two layers of soap. This property is different from that of binding with fatty substances and taking them with the movement of water.
Whenever soap is used, this chemical attraction reaction between greasy parts (stains) and water occurs.
Myth: a soap only washes well if it bubbles. Actually, the ability to foam is the ability of soap to trap a film of water between two layers of soap. This property is different from that of binding with fatty substances and taking them with the movement of water.
Soap making at home nowadays
I will summarize the stages of the manufacturing process of soap. This is cold saponification. For more details, I advise you to inquire with qualified people.
In summary, to make a soap, you must first weigh its fatty substance and do the calculations (with calculation software like SoapCalc) to find out the necessary amount of water and sodium hydroxide for the reaction. Then, heat the fat until the fat is melted. Meanwhile, mix the water and sodium hydroxide under a working hood. This first mixture is exothermic, it creates heat. The two mixtures (fatty substance and sodium hydroxide solution) are cooled until they reach a temperature of 120 ° F (49 ° C).
At this time, we mix everything together vigorously using a mixing foot until the consistency thickens a little and the appearance of the mixture becomes cloudy. Now is the time to add essential oils, if desired. Then, pour the mixture into the molds and forget about them for 4 to 6 weeks. This delay is essential because it makes it possible to complete the chemical reaction described above. If the soap is used before, it will be alkaline and irritating to the skin.
** Please note that handling sodium hydroxide is risking getting chemical burns: the wearing protective clothing, gloves and glasses is compulsory. **
In summary, to make a soap, you must first weigh its fatty substance and do the calculations (with calculation software like SoapCalc) to find out the necessary amount of water and sodium hydroxide for the reaction. Then, heat the fat until the fat is melted. Meanwhile, mix the water and sodium hydroxide under a working hood. This first mixture is exothermic, it creates heat. The two mixtures (fatty substance and sodium hydroxide solution) are cooled until they reach a temperature of 120 ° F (49 ° C).
At this time, we mix everything together vigorously using a mixing foot until the consistency thickens a little and the appearance of the mixture becomes cloudy. Now is the time to add essential oils, if desired. Then, pour the mixture into the molds and forget about them for 4 to 6 weeks. This delay is essential because it makes it possible to complete the chemical reaction described above. If the soap is used before, it will be alkaline and irritating to the skin.
** Please note that handling sodium hydroxide is risking getting chemical burns: the wearing protective clothing, gloves and glasses is compulsory. **
The manufacture of soap in the eighteenth century, according to the Diderot and d'Alembert Encyclopedia
The articles were consulted on the ENCCRE website. The saponification process seems to be hot and includes many more steps than the above-mentioned twenty-first century method. The steps mentioned here are my interpretation according to my knowledge in soap making and the chemical process described above. The stages are those of the soap factory and do not represent the domestic manufacture that could be done at that time. I have not yet found sources describing the manufacture and use of household soap in the 18th century.
First step: make sodium hydroxide (NaOH)
You guessed it, sodium hydroxide is not found in this form in nature. Here is what people of the 18th century did to make it. First, crush the Alicante soda (Mediterranean region known for soda quarries) to the size of hazelnuts or finer. The mineral soda is essentially formed from Na2CO3 molecules. It is mentioned that regions that do not have this type of stone use plant ash, ideally sea plants or those from riverbanks.
In equal volume, Alicante soda and quicklime (CaO) are placed in a tank with a tap at the bottom. Water is poured over the mixture of the two dusty stones. The tap is opened to collect the resulting basic solution, a solution containing sodium hydroxide (NaOH) and probably other molecules that I have not identified. This solution is called ''lessive'' (detergent). Three types of ''lessive'' is recovered according to the concentration of the solution and are differentiated by their density. Densities are calculated with the flotation of a fresh egg. For your information, a fresh egg sinks to the bottom of the water.
Second step: first cooking
In a cauldron, the olive oil and the weak detergent are put to heat. When the mixture is hot, that is to say it forms waves and broths, weak ''lessive'' is added until there is coagulation. From there, we change to add poor ''lessive'' until the mixture is consistent. Then, pour bucket to bucket of strong ''lessive'' to make the dough rise. When the dough has risen, it is removed from the heat and allowed to cool. During the whole process, the fire is maintained for a high temperature.
When the dough has cooled, it is collected and the excess detergent is discarded.
Third step: the cooking
We put the dough back in the cooking cauldron with 1 to 2 buckets of strong ''lessive'' over very high heat. The strong detergent is poured repeatedly until the dough is hardened. Then, using a wooden instrument on a pole, a worker makes a hole in the dough to let poor ''lessive'' flow, 3-4 buckets in 3-4 different places.
Thereafter, the dough is boiled in large broths for two hours. The texture of the dough should look like honey. It is removed from the heat and allowed to cool for one day. (The chemical reaction itself produces heat, the cooling time is long)
Fourth step: the molding
For the manufacture of white soap, the inside of the molds is covered with sifted slaked lime. This allows for more oxygen in the finished product and the oxygen allows better bleaching. This step is omitted for marbled soap.
In the marbled soap is added red clay (cinnabar earth) which gives the reddish color and the “coupe-rose” which gives a bluish color. No additional details are given on this type of soap.
After the dough has cooled for a day, it is transferred to molds or wooden boxes having a slope and an orifice at the end of the slope to let the water flow which will be reused for doing laundry.
After a while, the dough will be cool enough to be cut into bricks. The manufacturing process lasts a month in summer against fifteen to eighteen days in winter.
First step: make sodium hydroxide (NaOH)
You guessed it, sodium hydroxide is not found in this form in nature. Here is what people of the 18th century did to make it. First, crush the Alicante soda (Mediterranean region known for soda quarries) to the size of hazelnuts or finer. The mineral soda is essentially formed from Na2CO3 molecules. It is mentioned that regions that do not have this type of stone use plant ash, ideally sea plants or those from riverbanks.
In equal volume, Alicante soda and quicklime (CaO) are placed in a tank with a tap at the bottom. Water is poured over the mixture of the two dusty stones. The tap is opened to collect the resulting basic solution, a solution containing sodium hydroxide (NaOH) and probably other molecules that I have not identified. This solution is called ''lessive'' (detergent). Three types of ''lessive'' is recovered according to the concentration of the solution and are differentiated by their density. Densities are calculated with the flotation of a fresh egg. For your information, a fresh egg sinks to the bottom of the water.
- Strong ''lessive'': a fresh egg floats on the water (high density)
- Poor ''lessive: a fresh egg at the tip that falls on the water (moderate density)
- Weak ''lessive'': a fresh egg floats between two waters (low density)
Second step: first cooking
In a cauldron, the olive oil and the weak detergent are put to heat. When the mixture is hot, that is to say it forms waves and broths, weak ''lessive'' is added until there is coagulation. From there, we change to add poor ''lessive'' until the mixture is consistent. Then, pour bucket to bucket of strong ''lessive'' to make the dough rise. When the dough has risen, it is removed from the heat and allowed to cool. During the whole process, the fire is maintained for a high temperature.
When the dough has cooled, it is collected and the excess detergent is discarded.
Third step: the cooking
We put the dough back in the cooking cauldron with 1 to 2 buckets of strong ''lessive'' over very high heat. The strong detergent is poured repeatedly until the dough is hardened. Then, using a wooden instrument on a pole, a worker makes a hole in the dough to let poor ''lessive'' flow, 3-4 buckets in 3-4 different places.
Thereafter, the dough is boiled in large broths for two hours. The texture of the dough should look like honey. It is removed from the heat and allowed to cool for one day. (The chemical reaction itself produces heat, the cooling time is long)
Fourth step: the molding
For the manufacture of white soap, the inside of the molds is covered with sifted slaked lime. This allows for more oxygen in the finished product and the oxygen allows better bleaching. This step is omitted for marbled soap.
In the marbled soap is added red clay (cinnabar earth) which gives the reddish color and the “coupe-rose” which gives a bluish color. No additional details are given on this type of soap.
After the dough has cooled for a day, it is transferred to molds or wooden boxes having a slope and an orifice at the end of the slope to let the water flow which will be reused for doing laundry.
After a while, the dough will be cool enough to be cut into bricks. The manufacturing process lasts a month in summer against fifteen to eighteen days in winter.
Laundry Thoughts
I plan to do a full article on garment care but for now I want to share some thoughts. The use of the word ''lessive'' in the 18th century refers to a basic and corrosive solution, as described earlier (today it refers as laundry most of the time). ''Lessive'' burns the hands if they stay in contact for too long. In fact, when the laundry was done, the clothes were boiled in ''lessive'' to saponify the grease stains and then remove them. This explanation is highlighted in the Diderot and D'Alembert Encyclopedia. The process was much longer and more aggressive for laundry than the modern washing machine and detergents. This is the reason why only white or unbleached linen was washed. The ceremonial clothes were cleaned but not washed because the process would have removed their colors.
What do my first soaps look like?
Finally, I want to show you the two soaps I made with my friend. They are inspired by the 18th century.
The first is a high class soap. The fatty substance is olive oil and a little castor oil has been added to promote foaming. The essential oils used were citrus oils: orange, grapefruit, lemon and clementine.
The second soap is a more `` affordable '' soap based on lard and also a little castor oil to promote foaming. The essential oils used are repellents for natural insects: lavender and cloves.
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| Left, lard soap scented with lavender and cloves On the right, the soap based on olive oil perfumed with citrus fruits |
Here, a rare article almost without photo. I hope that some courageous people will have reached the end of the reading.
This is the first article that I used a translation tool to help me with the translation.
Mlle Canadienne
This is the first article that I used a translation tool to help me with the translation.
Mlle Canadienne
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