In chemistry,
soap is a salt of a
fatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
.
[IUPAC. "IUPAC Gold Book – soap" Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. . Accessed 2010-08-09] Soaps are mainly used as
surfactantSurfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
s for
washingWashing is one way of cleaning, namely with water and often some kind of soap or detergent. Washing is an essential part of good hygiene and health....
,
bathingBathing is the washing or cleansing of the body in a fluid, usually water or an aqueous solution. It may be practised for personal hygiene, religious ritual or therapeutic purposes or as a recreational activity....
, and cleaning, but they are also used in textile spinning and are important components of
lubricantA lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...
s.
Soaps for cleansing are obtained by treating vegetable or animal oils and fats with a strongly
alkalineAlkalinity or AT measures the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric sum of the bases in solution...
solution. Fats and oils are composed of triglycerides: three molecules of fatty acids attached to a single molecule of
glycerolGlycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
. The alkaline solution, often called
lyeLye is a corrosive alkaline substance, commonly sodium hydroxide or historically potassium hydroxide . Previously, lye was among the many different alkalis leached from hardwood ashes...
, brings about a chemical reaction known as
saponificationSaponification is a process that produces soap, usually from fats and lye. In technical terms, saponification involves base hydrolysis of triglycerides, which are esters of fatty acids, to form the sodium salt of a carboxylate. In addition to soap, such traditional saponification processes...
. In saponification, the fats are first hydrolyzed into free fatty acids, which then combine with the alkali to form crude soap. Glycerol, often called glycerine, is liberated and is either left in or washed out and recovered as a useful by-product according to the process employed.
Soaps are key components of most lubricating greases, which are usually emulsions of
calcium soapCalcium stearate is carboxylate of calcium that is found in some lubricants and surfactants. It is a white waxy powder.-Production and occurrence:Calcium stearate is produced by heating stearic acid, a fatty acid, and calcium oxide:...
or
lithiumLithium stearate is a chemical compound with the formula LiO2C16CH3. It is formally classified as a soap . Lithium stearate is a white soft solid, prepared by the reaction of lithium hydroxide and steric acid....
soaps and mineral oil. These calcium- and lithium-based
greaseGrease may refer to:* Grease , a type of industrial lubricant* Yellow grease, in rendering, used frying oils, or lower-quality grades of tallow...
s are widely used. Many other metallic soaps are also useful, including those of aluminium, sodium, and mixtures of them. Such soaps are also used as thickeners to increase the viscosity of oils. In ancient times, lubricating greases were made by the addition of lime to
olive oilOlive oil is an oil obtained from the olive , a traditional tree crop of the Mediterranean Basin. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and as a fuel for traditional oil lamps...
.
[Thorsten Bartels et al. "Lubricants and Lubrication" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Weinheim. ]
Mechanism of cleansing soaps
When used for cleaning, soap serves as a
surfactantSurfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
in conjunction with
waterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. The cleaning action of this mixture is attributed to the action of micelles, tiny spheres coated on the outside with polar hydrophilic (water loving) groups, encasing a lipophilic (fat loving) pocket that can surround the grease particles, causing them to disperse in water. The lipophilic portion is made up of the long
hydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
chain from the fatty acid. In other words, whereas normally oil and water do not mix, the addition of soap allows oils to disperse in water and be rinsed away. Synthetic
detergentA detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...
s operate by similar mechanisms to soap.
Effect of the alkali
The type of alkali metal used determines the kind of soap produced. Sodium soaps, prepared from
sodium hydroxide, are firm, whereas potassium soaps, derived from
potassium hydroxidePotassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
, are softer or often liquid. Historically, potassium hydroxide was extracted from the ashes of
brackenBracken are several species of large, coarse ferns of the genus Pteridium. Ferns are vascular plants that have alternating generations, large plants that produce spores and small plants that produce sex cells . Brackens are in the family Dennstaedtiaceae, which are noted for their large, highly...
or other plants. Lithium soaps also tend to be hard—these are used exclusively in
greaseThe term grease is used to describe semisolid lubricants. Although the word grease is also used to describe rendered fat of animals, in the context of lubrication, grease typically applies to a material consisting of a soap emulsified with mineral or vegetable oil...
s.
Effects of fats
Soaps are derivatives of
fatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...
s. Traditionally they have been made from
triglycerideA triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....
s (oils and fats). Triglyceride is the chemical name for the tri
esterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s of fatty acids and glycerin. Tallow,
i.e., rendered beef fat, is the most available triglyceride from animals. Its saponified product is called
sodium tallowate. Typical vegetable oils used in soap making are palm oil, coconut oil, olive oil and laurel oil. Each species offers quite different fatty acid content and hence results in soaps of distinct feel. The seed oils give softer but milder soaps. Soap made from pure
olive oilOlive oil is an oil obtained from the olive , a traditional tree crop of the Mediterranean Basin. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and as a fuel for traditional oil lamps...
is sometimes called
Castile soapCastile soap is a name used in English-speaking countries for olive oil based soap made in a style similar to that originating in the Castile region of Spain.-History:...
or
Marseille soapMarseille soap or Savon de Marseille is a traditional soap made from vegetable oils that has been made around Marseille, France, for about 600 years, the first documented soapmaker in the area being recorded in about 1370...
and is reputed for extra mildness. The term "Castile" is also sometimes applied to soaps from a mixture of oils, but a high percentage of olive oil.
Fatty acid content of various fats used for soap-making
| | Lauric acid | Myristic acid | Palmitic acid | Stearic acid | Oleic acid | Linoleic acid | Linolenic acid |
| fats | C12, saturated | C14 saturated | C16 saturated | C18 saturated | C18 monounsaturated | C18 diunsaturated | C18 triunsaturated |
| Tallow Tallow is a rendered form of beef or mutton fat, processed from suet. It is solid at room temperature. Unlike suet, tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation.In industry,...
|
0 |
4 |
28 |
23 |
35 |
2 |
1 |
Coconut oilCoconut oil is an edible oil extracted from the kernel or meat of matured coconuts harvested from the coconut palm . Throughout the tropical world, it has provided the primary source of fat in the diets of millions of people for generations. It has various applications in food, medicine, and industry...
|
48 |
18 |
9 |
3 |
7 |
2 |
0 |
| Palm kernel oil Palm kernel oil is an edible plant oil derived from the kernel of the oil palm Elaeis guineensis. It should not be confused with the other two edible oils derived from palm fruits: coconut oil, extracted from the kernel of the coconut, and palm oil, extracted from the pulp of the oil palm...
|
46 |
16 |
8 |
3 |
12 |
2 |
0 |
| Laurel oil |
54 |
0 |
0 |
0 |
15 |
17 |
0 |
Olive oilOlive oil is an oil obtained from the olive , a traditional tree crop of the Mediterranean Basin. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and as a fuel for traditional oil lamps...
|
0 |
0 |
11 |
2 |
78 |
10 |
0 |
CanolaCanola refers to a cultivar of either Rapeseed or Field Mustard . Its seeds are used to produce edible oil suitable for consumption by humans and livestock. The oil is also suitable for use as biodiesel.Originally, Canola was bred naturally from rapeseed in Canada by Keith Downey and Baldur R...
|
0 |
1 |
3 |
2 |
58 |
9 |
23 |
Early history
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in Ancient
BabylonBabylon was an Akkadian city-state of ancient Mesopotamia, the remains of which are found in present-day Al Hillah, Babil Province, Iraq, about 85 kilometers south of Baghdad...
. In the reign of
NabonidusNabonidus was the last king of the Neo-Babylonian Empire, reigning from 556-539 BCE.-Historiography on Nabonidus:...
(556–539 BCE) a recipe for soap consisted of
uhulu [ashes], cypress [oil] and sesame [seed oil] "for washing the stones for the servant girls". A formula for soap consisting of water,
alkaliIn chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
, and cassia oil was written on a Babylonian clay tablet around 2200 BC.
The
Ebers papyrusThe Ebers Papyrus, also known as Papyrus Ebers, is an Egyptian medical papyrus dating to circa 1550 BC. Among the oldest and most important medical papyri of ancient Egypt, it was purchased at Luxor, in the winter of 1873–74 by Georg Ebers...
(Egypt, 1550 BC) indicates that
ancient EgyptAncient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...
ians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention that a soap-like substance was used in the preparation of
woolWool is the textile fiber obtained from sheep and certain other animals, including cashmere from goats, mohair from goats, qiviut from muskoxen, vicuña, alpaca, camel from animals in the camel family, and angora from rabbits....
for weaving.
Roman history
The word
sapo, Latin for soap, first appears in
Pliny the ElderGaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...
's
Historia Naturalis, which discusses the manufacture of soap from
tallowTallow is a rendered form of beef or mutton fat, processed from suet. It is solid at room temperature. Unlike suet, tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation.In industry,...
and ashes, but the only use he mentions for it is as a
pomadePomade is a greasy or waxy substance that is used to style hair. Pomade makes hair look slick and shiny. Unlike hair spray and hair gel, pomade does not dry and often takes several washes to remove...
for hair; he mentions rather disapprovingly that among the
GaulGaul was a region of Western Europe during the Iron Age and Roman era, encompassing present day France, Luxembourg and Belgium, most of Switzerland, the western part of Northern Italy, as well as the parts of the Netherlands and Germany on the left bank of the Rhine. The Gauls were the speakers of...
s and
GermansThe Teutons or Teutones were mentioned as a Germanic tribe by Greek and Roman authors, notably Strabo and Marcus Velleius Paterculus and normally in close connection with the Cimbri, whose ethnicity is contested between Gauls and Germani...
men are likelier to use it than women.
Aretaeus of CappadociaAretaeus , is one of the most celebrated of the ancient Greek physicians, of whose life, however, few particulars are known. There is some uncertainty regarding both his age and country, but it seems probable that he practised in the 1st century CE, during the reign of Nero or Vespasian...
, writing in the first century AD, observes among "Celts, which are men called Gauls, those alkaline substances that are made into balls, called
soap".
A popular belief encountered in some places claims that soap takes its name from a supposed
Mount SapoMount Sapo is a fictional mountain supposed to exist somewhere near Rome, presumably in Italy. It appears in a fanciful rewriting of the history of soap, and it is often claimed to explain the origins of the name...
, where animal sacrifices were supposed to take place—tallow from these sacrifices would then have mixed with ashes from fires associated with these sacrifices and with water to produce soap. But there is no evidence of a Mount Sapo within the Roman world and no evidence for the
apocryphaThe term apocrypha is used with various meanings, including "hidden", "esoteric", "spurious", "of questionable authenticity", ancient Chinese "revealed texts and objects" and "Christian texts that are not canonical"....
l story. The
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
word
sapo simply means "soap"; it was likely borrowed from an early Germanic language and is
cognateIn linguistics, cognates are words that have a common etymological origin. This learned term derives from the Latin cognatus . Cognates within the same language are called doublets. Strictly speaking, loanwords from another language are usually not meant by the term, e.g...
with Latin
sebum, "tallow", which appears in Pliny the Elder's account. Roman animal
sacrificeSacrifice is the offering of food, objects or the lives of animals or people to God or the gods as an act of propitiation or worship.While sacrifice often implies ritual killing, the term offering can be used for bloodless sacrifices of cereal food or artifacts...
s usually burned only the bones and inedible entrails of the sacrificed animals; edible meat and fat from the sacrifices were taken by the humans rather than the gods.
Zosimos of PanopolisZosimos of Panopolis was an Egyptian or Greek alchemist and Gnostic mystic from the end of the 3rd and beginning of the 4th century AD. He was born in Panopolis, present day Akhmim in the south of Egypt, ca. 300. He wrote the oldest known books on alchemy, of which quotations in the Greek language...
ca. 300 AD describes soap and soapmaking.
GalenAelius Galenus or Claudius Galenus , better known as Galen of Pergamon , was a prominent Roman physician, surgeon and philosopher...
describes soap-making using lye and prescribes washing to carry away impurities from the body and clothes. According to Galen, the best soaps were German, and soaps from Gaul were second best. This is a reference to true soap in antiquity.
Medieval history
Soap-makers in Naples were members of a
guildA guild is an association of craftsmen in a particular trade. The earliest types of guild were formed as confraternities of workers. They were organized in a manner something between a trade union, a cartel, and a secret society...
in the late sixth century, and in the 8th century, soap-making was well-known in Italy and Spain. The
CarolingianThe Carolingian dynasty was a Frankish noble family with origins in the Arnulfing and Pippinid clans of the 7th century AD. The name "Carolingian", Medieval Latin karolingi, an altered form of an unattested Old High German *karling, kerling The Carolingian dynasty (known variously as the...
capitularyA capitulary was a series of legislative or administrative acts emanating from the Frankish court of the Merovingian and Carolingian dynasties, especially that of the first emperor, Charlemagne...
De Villis, dating to around 800, representing the royal will of
CharlemagneCharlemagne was King of the Franks from 768 and Emperor of the Romans from 800 to his death in 814. He expanded the Frankish kingdom into an empire that incorporated much of Western and Central Europe. During his reign, he conquered Italy and was crowned by Pope Leo III on 25 December 800...
, mentions soap as being one of the products the stewards of royal estates are to tally. Soap-making is mentioned both as "women's work" and the produce of "good workmen" alongside other necessities such as the produce of carpenters, blacksmiths, and bakers.
15th–20th centuries
In France, by the second half of the 15th century the semi-industrialized professional manufacture of soap was concentrated in a few centers of
ProvenceProvence ; Provençal: Provença in classical norm or Prouvènço in Mistralian norm) is a region of south eastern France on the Mediterranean adjacent to Italy. It is part of the administrative région of Provence-Alpes-Côte d'Azur...
—
ToulonToulon is a town in southern France and a large military harbor on the Mediterranean coast, with a major French naval base. Located in the Provence-Alpes-Côte-d'Azur region, Toulon is the capital of the Var department in the former province of Provence....
,
HyèresHyères , Provençal Occitan: Ieras in classical norm or Iero in Mistralian norm) is a commune in the Var department in the Provence-Alpes-Côte d'Azur region in southeastern France....
and
MarseilleMarseille , known in antiquity as Massalia , is the second largest city in France, after Paris, with a population of 852,395 within its administrative limits on a land area of . The urban area of Marseille extends beyond the city limits with a population of over 1,420,000 on an area of...
— which supplied the rest of France. In Marseilles, by 1525, production was concentrated in at least two factories, and soap production at Marseille tended to eclipse the other Provençal centers. English manufacture tended to concentrate in London.
Finer soaps were later produced in Europe from the 16th century, using vegetable oils (such as
olive oilOlive oil is an oil obtained from the olive , a traditional tree crop of the Mediterranean Basin. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and as a fuel for traditional oil lamps...
) as opposed to animal fats. Many of these soaps are still produced, both industrially and by small scale artisans.
Castile soapCastile soap is a name used in English-speaking countries for olive oil based soap made in a style similar to that originating in the Castile region of Spain.-History:...
is a popular example of the vegetable-only soaps derived by the oldest "white soap" of Italy.
In modern times, the use of soap has become universal in industrialized nations due to a better understanding of the role of
hygieneHygiene refers to the set of practices perceived by a community to be associated with the preservation of health and healthy living. While in modern medical sciences there is a set of standards of hygiene recommended for different situations, what is considered hygienic or not can vary between...
in reducing the population size of pathogenic microorganisms. Industrially manufactured bar soaps first became available in the late eighteenth century, as advertising campaigns in Europe and the United States promoted popular awareness of the relationship between cleanliness and health.
Until the
Industrial RevolutionThe Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...
, soapmaking was conducted on a small scale and the product was rough.
Andrew PearsAndrew Pears was farmer's son from Cornwall, born in 1766, who invented the transparent soap. He moved to London in 1789 from his home in Mevagissey, Cornwall, where he had trained as a barber....
started making a high-quality, transparent soap in 1789 in
LondonLondon is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
. His son-in-law,
Thomas J. BarrattThomas J. Barratt was the chairman of the soap manufacturer A&F Pears and a pioneer of brand marketing. He has been called "the father of modern advertising"....
, opened a factory in
IsleworthIsleworth is a small town of Saxon origin sited within the London Borough of Hounslow in west London, England. It lies immediately east of the town of Hounslow and west of the River Thames and its tributary the River Crane. Isleworth's original area of settlement, alongside the Thames, is known as...
in 1862.
William GossageWilliam Gossage was a chemical manufacturer who established a soap making business in Widnes, Lancashire, England.-Early life:...
produced low-price good-quality soap from the 1850s. Robert Spear Hudson began manufacturing a soap powder in 1837, initially by grinding the soap with a
mortar and pestleA mortar and pestle is a tool used to crush, grind, and mix solid substances . The pestle is a heavy bat-shaped object, the end of which is used for crushing and grinding. The mortar is a bowl, typically made of hard wood, ceramic or stone...
. American manufacturer
Benjamin T. BabbittBenjamin Talbot Babbitt was a self-made American businessman and inventor who amassed a fortune in the soap industry, manufacturing Babbitt's Best Soap.-Early life:...
introduced marketing innovations that included sale of bar soap and distribution of product samples. William Hesketh Lever and his brother, James, bought a small soap works in
WarringtonWarrington is a town, borough and unitary authority area of Cheshire, England. It stands on the banks of the River Mersey, which is tidal to the west of the weir at Howley. It lies 16 miles east of Liverpool, 19 miles west of Manchester and 8 miles south of St Helens...
in 1886 and founded what is still one of the largest soap businesses, formerly called Lever Brothers and now called
UnileverUnilever is a British-Dutch multinational corporation that owns many of the world's consumer product brands in foods, beverages, cleaning agents and personal care products....
. These soap businesses were among the first to employ large scale
advertisingAdvertising is a form of communication used to persuade an audience to take some action with respect to products, ideas, or services. Most commonly, the desired result is to drive consumer behavior with respect to a commercial offering, although political and ideological advertising is also common...
campaigns.
Soap making processes
The industrial production of soap involves continuous processes, involving continuous addition of fat and removal of product. Smaller scale production involve the traditional
batch processBatch process may refer to:* Batch processing * Batch production...
es. There are three variations: the
cold-process, wherein the reaction takes place substantially at room temperature, the
semi-boiled or
hot-process, wherein the reaction takes place at near-boiling point, and the
fully boiled process, wherein the reactants are boiled at least once and the glycerol recovered. The cold-process and hot-process (semi-boiled) are the simplest and typically used by small artisans and hobbyists producing handmade decorative soaps and similar. The glycerine remains in the soap and the reaction continues for many days after the soap is poured into moulds. In the hot-process method, also, the glycerine is left in but at the high temperature employed; the reaction is practically completed in the kettle, before the soap is poured into moulds. This process is simple and quick and is the one employed in small factories all over the world.
Handmade soap from the cold process also differs from industrially made soap in that an excess of fat is used, beyond that which is used to consume the alkali (in a cold-pour process this excess fat called "superfatting"), and the glycerine left in acts as moisturizing agent. However, it also makes the soap softer and less resistant to becoming "mushy" if left wet. Soap from the hot process, also, has left-over glycerine (as it is better to add too much oil and have left-over fat, than to add too much lye and have left-over lye) and the related pros and cons. Further addition of glycerine and processing of this soap produces
glycerin soapGlycerin soaps are soaps that contain glycerin, a component of fat or oil. The soap is recognizably different from other soaps because it is translucent. The clarity of the soap is due to the particular alignment of the soap molecules in this type of soap, which can be induced through the addition...
. Superfatted soap, which contains excess fat, is more skin-friendly than one without extra fat. However, if too much fat is added, it can leave a "greasy" feel to their skin. Sometimes an emollient additive such as
jojobaJojoba, pronounced , is a shrub native to the Sonoran and Mojave deserts of Arizona, California, and Mexico. It is the sole species of the family Simmondsiaceae, placed in the order Caryophyllales. It is also known as goat nut, deer nut, pignut, wild hazel, quinine nut, coffeeberry, and gray box...
oil or
shea butterShea butter is a slightly yellowish or ivory-colored fat extracted from the nut of the African shea tree . It is widely used in cosmetics as a moisturizer, salve or lotion. Shea butter is edible and may be used in food preparation...
is added "at trace" (in the cold process method, the point at which the saponification process is sufficiently advanced that the soap has begun to thicken) in the belief that nearly all the lye will be spent and it will escape saponification and remain intact, or, in the case of hot-process soap, after the initial oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process known as "lye discount", whereby, instead of adding extra fats, the soap maker uses less alkali than required.
Cold process
Even in the cold-soapmaking process, some heat is usually required for the process. The temperature is usually raised sufficiently to ensure complete melting of the fat being used. The batch may be kept warm for some time after mixing to ensure that the alkali (hydroxide) is completely used up. This soap is safe to use after approximately 12–48 hours, but is not at its peak quality for use for several weeks.
Cold-process soapmaking requires exact measurements of lye and fat amounts and computing their ratio, using saponification charts to ensure that the finished product does not contain any excess hydroxide or too much free unreacted fat. Saponification charts should also be used in hot-processes, but are not necessary for the "fully boiled hot-process" soaping.
A cold-process soapmaker first looks up the saponification value of the fats being used on a saponification chart. This value is used to calculate the appropriate amount of lye. Excess unreacted lye in the soap will result in a very high pH and can burn or irritate skin. Not enough lye, and the soap is greasy. Most soap makers formulate their recipes with a 4–10% deficit of lye so that all of the lye is converted and that excess fat is left for skin conditioning benefits.
The lye is dissolved in water. Then oils are heated, or melted if they are solid at room temperature. Once the oils are liquified and the lye is fully dissolved in water, they are combined. This lye-fat mixture is mixed until the two phases (oils and water) are fully emulsified. Emulsification is most easily identified visually when the soap exhibits some level of "trace", which is the thickening of the mixture. (Modern-day amateur soapmakers often use a stick blender to speed this process). There are varying levels of trace. Depending on how additives will affect trace, they may be added at light trace, medium trace, or heavy trace. After much stirring, the mixture turns to the consistency of a thin pudding. "Trace" corresponds roughly to viscosity.
Essential oilAn essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove...
s and
fragrance oilFragrance oil, also known as aroma oils, aromatic oils, and flavor oils, are blended synthetic aroma compounds or natural essential oils that are diluted with a carrier like propylene glycol, vegetable oil, or mineral oil...
s can be added with the initial soaping oils, but solid additives such as botanicals, herbs, oatmeal, or other additives are most commonly added at light trace, just as the mixture starts to thicken.
The batch is then poured into molds, kept warm with towels or blankets, and left to continue saponification for 12 to 48 hours. (Milk soaps or other soaps with sugars added are the exception. They typically do not require insulation, as the presence of sugar increases the speed of the reaction and thus the production of heat.) During this time, it is normal for the soap to go through a "gel phase," wherein the opaque soap will turn somewhat transparent for several hours, before once again turning opaque.
After the insulation period, the soap is firm enough to be removed from the mold and cut into bars. At this time, it is safe to use the soap, since saponification is in essence complete. However, cold-process soaps are typically cured and hardened on a drying rack for 2–6 weeks before use. During this cure period, trace amounts of residual lye is consumed by saponification and excess water evaporates.
Hot processes
Hot-processed soaps are created by encouraging the saponification reaction by adding heat to the reaction. This speeds the reaction. Unlike cold-processed soap, in hot-process soaping the oils are completely saponified by the end of the handling period, whereas with cold pour soap the bulk of the saponification happens after the oils and lye solution emulsification is poured into molds.
In the hot-process, the hydroxide and the fat are heated and mixed together 80–100 °C, a little below boiling point, until saponification is complete, which, before modern scientific equipment, the soapmaker determined by taste (the sharp, distinctive taste of the hydroxide disappears after it is saponified) or by eye; the experienced eye can tell when gel stage and full saponification has occurred. Beginners can find this information through research and classes. It is highly recommended not to "taste" soap for readiness. Sodium and potassium hydroxides when not saponified are a highly caustic materials.
An advantage of the fully boiled hot process in soap making is that the exact amount of hydroxide required need not be known with great accuracy. They originated when the purity of the alkali hydroxides were unreliable, as these processes can use even naturally found alkalis such as wood ashes and potash deposits. In the fully boiled process, the mix is actually boiled (100C+), and, after saponification has occurred, the "neat soap" is
precipitatedPrecipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
from the solution by adding common salt, and the excess liquid drained off. This excess liquid carries away with it much of the impurities and colour compounds in the fat, to leave a purer, whiter soap, and with practically all the glycerine removed. The hot, soft soap is then pumped into a mould. The spent hydroxide solution is processed for recovery of glycerine.
Moulds
Many commercially available soap moulds are made of silicone or various types of plastic, although many soap making hobbyists may use cardboard boxes lined with a plastic film. Soaps can be made in long bars that are cut into individual portions,
or cast into individual moulds.
Purification and finishing
In the fully boiled process on factory scale, the soap is further purified to remove any excess
sodium hydroxide,
glycerolGlycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
, and other impurities, colour compounds, etc. These components are removed by
boilingBoiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. While below the boiling point a liquid...
the crude soap
curdCurds are a dairy product obtained by curdling milk with rennet or an edible acidic substance such as lemon juice or vinegar, and then draining off the liquid portion. The increased acidity causes the milk proteins to tangle into solid masses, or curds. The remaining liquid, which contains only...
s in
waterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
and then precipitating the soap with salt.
At this stage, the soap still contains too much water, which has to be removed. This was traditionally done on a chill rolls, which produced the soap flakes commonly used in the 1940s and 1950s. This process was superseded by spray dryers and then by vacuum dryers.
The dry soap (approximately 6–12% moisture) is then compacted into small pellets or noodles. These pellets/noodles are now ready for soap finishing, the process of converting raw soap pellets into a saleable product, usually bars.
Soap pellets are combined with fragrances and other materials and blended to homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into a refiner, which, by means of an
augerAn auger is a drilling device, or drill bit, that usually includes a rotating helical screw blade called a "flighting" to act as a screw conveyor to remove the drilled out material...
, forces the soap through a fine
wireA wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
screen. From the refiner, the soap passes over a roller mill (French milling or hard milling) in a manner similar to calendering paper or plastic or to making
chocolate liquorChocolate liquor is pure chocolate in its liquid form. Like the cocoa beans from which it is produced, it contains both cocoa solids and cocoa butter in roughly equal proportion....
. The soap is then passed through one or more additional refiners to further plasticize the soap mass. Immediately before extrusion, the mass is passed through a vacuum chamber to remove any trapped air. It is then extruded into a long log or blank, cut to convenient lengths, passed through a metal detector, and then stamped into shape in refrigerated tools. The pressed bars are packaged in many ways.
SandSand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
or
pumicePumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
may be added to produce a scouring soap. The scouring agents serve to remove dead skin cells from the surface being cleaned. This process is called
exfoliationExfoliation involves the removal of the oldest dead skin cells on the skin's outermost surface, and has been used for many years to help maintain skin. Exfoliation is involved in the process of all facials, during microdermabrasion or chemical peels at medical spas...
. Many newer materials that are effective but do not have the sharp edges and poor particle size distribution of pumice are used for exfoliating soaps.
Nanoscopic metals are commonly added to certain soaps specifically for both coloration and anti-bacterial properties.
TitaniumTitanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
powder is commonly used in extreme "white" soaps for these purposes;
nickelNickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
,
aluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, and
silverSilver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
are less commonly used. These metals exhibit an electron-robbing behavior when in contact with bacteria, stripping electrons from the organism's surface, thereby disrupting their functioning and killing them. Because some of the metal is left behind on the skin and in the pores, the benefit can also extend beyond the actual time of washing, helping reduce bacterial contamination and reducing potential odors from bacteria on the skin surface.
See also
- Aleppo soap
Aleppo soap is a handmade, hard bar soap. Aleppo soap is also known as savon d'Alep, laurel soap, or ghar soap . It derives its English and French names from the city of Aleppo, Syria, where it is reputed to have been made for thousands of years...
- Castile soap
Castile soap is a name used in English-speaking countries for olive oil based soap made in a style similar to that originating in the Castile region of Spain.-History:...
- Marseille soap
Marseille soap or Savon de Marseille is a traditional soap made from vegetable oils that has been made around Marseille, France, for about 600 years, the first documented soapmaker in the area being recorded in about 1370...
- Nabulsi soap
Nabulsi soap is a type of castile soap produced only in Nablus in the West Bank, Palestine. An olive oil-based soap, it is made up of three primary ingredients: virgin olive oil, water, and a sodium compound...
- Vegetarian soap
-Olive oil soaps:*Aleppo soap, a Syrian style of soap noted for the inclusion of Laurel oil in its formulation*Castile soap, a wide ranging style of soap in English speaking countries, as originally made in the Castile region of Spain...
- Soap substitute
A soap substitute refers to detergents or cleansing creams, other than soap, for cleaning the skin, especially removing greasy films or glandular exudates. Soap substitutes can be made from a variety of sources including plants with high saponin levels...
- Foam
-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...
- Soap bubble
A soap bubble is a thin film of soapy water enclosing air, that forms a hollow sphere with an iridescent surface. Soap bubbles usually last for only a few seconds before bursting, either on their own or on contact with another object. They are often used for children's enjoyment, but they are also...
- Soap dish
A soap dish holds a bar of soap when not in use for hand washing or other cleaning, near a washing area such as a bathtub or washbasin. Soap dishes are made from waterproof materials such as plastic, ceramic and metal. Soap dishes may be mounted on the wall. For liquid soap or foam soap a soap...
- Soap dispenser
A soap dispenser is a device that, when manipulated or triggered appropriately, yields soap . It can be manually operated by means of a handle, or can be automatic...
- Soap plant
The Soap Plants, Soaproots or Amoles are the genus Chlorogalum of flowering plants. Less common names for them include Soap Lilies. They are endemic to western North America, from Oregon to Baja California, and are mostly found in California.The Soap Plants grow as perennial plants, from a bulb,...
Further reading
- Garzena, Patrizia-Tadiello, Marina (2004). Soap Naturally—Ingredients, methods and recipes for natural handmade soap. Online information and Table of Contents. ISBN 978-0-9756764-0-0
- Thomssen, E. G., Ph. D. (1922). Soap-Making Manual Free ebook at Project Gutenberg
- Mohr, Merilyn (1979). "The Art of Soap Making". A Harrowsmith Contemporary Primer. Firefly Books. ISBN 978-0920656037
- Dunn, Kevin M. (2010) " Scientific Soapmaking: The Chemistry of Cold Process" Clavicula Press. ISBN 978-1935652090
External links