Soap is an
anionicIn chemistry, an anionic species is one that contains a full negative charge. These types of compounds can range in reactivity, but most are fairly reactive....
surfactantSurfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids.- Etymology :The term surfactant is a blend of surface active agent...
used in conjunction with
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
for washing and cleaning, which historically comes either in solid
barsMolding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....
or in the form of a viscous
liquidLiquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material. The surface is a free surface where the liquid is not constrained by a container....
.
Soap consists of
sodiumSodium is a metallic element with a symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1"...
or
potassiumPotassium is the chemical element with the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash...
salts of
fatty acidIn chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail , which is either saturated or unsaturated...
s and is obtained by reacting common oils or fats with a strong alkaline solution (the base, popularly referred to as
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...
) in a process known as
saponificationSaponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid . Saponification is commonly used to refer to the reaction of a metallic alkali with a fat or oil to form soap. Saponifiable substances are those that can be converted into...
. The fats are
hydrolyzedHydrolysis is a chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions, which may go on to participate in further reactions. It is the type of reaction that is used to break down certain polymers, especially those made by step-growth polymerization...
by the base, yielding
alkaliIn chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Alkalis are best known for being bases that dissolve in water. Bases are compounds with a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base, especially for...
salts of fatty acids (crude soap) and
glycerolGlycerol is an organic compound, also commonly called glycerin or glycerine. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydrophilic hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. ...
.
Today, soap is often replaced by other cleaning agents, such as synthetic
detergentA detergent is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning...
s.
Overview
Soaps are useful for cleaning because soap
moleculeA molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense...
s have both a hydrophilic end, which dissolves in
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
, as well as a hydrophobic end, which is able to dissolve nonpolar
greaseFats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...
molecules. Although grease will normally adhere to skin or clothing, the soap molecules can form micelles which surround the grease particles and allow them to be dissolved in water. Applied to a soiled surface, soapy water effectively holds particles in colloidal suspension so it can be rinsed off with clean water. The hydrophobic portion (made up of a long
hydrocarbonIn organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. With relation to chemical terminology, aromatic hydrocarbons or arenes, alkanes, alkenes and alkyne-based compounds composed entirely of carbon and hydrogen are referred to as "pure"...
chain) dissolves dirt and oils, while the ionic end dissolves in water. Therefore, it allows water to remove normally-insoluble matter by emulsification.
In other words, while normally oil and water do not mix, the addition of soap allows oils to dissolve in water, allowing them to be rinsed away.
Early history
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in Ancient
BabylonBabylon was a 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...
. 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. Alkalis are best known for being bases that dissolve in water. Bases are compounds with a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base, especially for...
and cassia oil was written on a Babylonian clay tablet around 2200 BC.
The
Ebers papyrusThe Ebers Papyrus of about 1550 BC is among the most important medical papyri of ancient Egypt. It is also commonly called Papyrus Ebers[ at WorldCat.] . It is one of the two oldest preserved medical documents anywhere, the other main source being the Edwin Smith papyrus...
(Egypt, 1550 BC) indicates that
ancient EgyptAncient Egypt was an ancient civilization of eastern North Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. The civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh, and...
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 a fibrous protein derived from the specialized skin cells called follicles. The wool is taken from animals in the Caprinae family, principally sheep, but the hair of certain species of other mammals including: goats, llamas, and rabbits may also be called wool...
for weaving.
Roman history
It had been reported that a factory producing soap-like substances was found in the ruins of
PompeiiPompeii is a ruined and partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei...
(AD 79). However, this has proven to be a misinterpretation of the survival of some soapy mineral substance, probably
soapstoneSoapstone is a metamorphic rock, a talc-schist. It is largely composed of the mineral talc and is rich in magnesium. It is produced by dynamothermal metamorphism and metasomatism, which occurs in the areas where tectonic plates are subducted, changing rocks by heat and pressure, with influx of...
at the Fullonica where it was used for dressing recently cleansed textiles. Unfortunately this error has been repeated widely and can be found in otherwise reputable texts on soap history. The ancient Romans were generally ignorant of soap's detergent properties, and made use of the
strigilA strigil was a small, curved, metal tool used in ancient Greece and Rome to scrape dirt and sweat from the body before effective soaps became available. First perfumed oil was applied to the skin, and then it would be scraped off, along with the dirt. For wealthier people, this process was often...
to scrape dirt and sweat from the body. The word "soap" (Latin
sapo) appears first in a European language in
Pliny the ElderGaius Plinius Secundus , better known as Pliny the Elder, was an 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 NaturalisHistoria Naturalis may refer to:*Natural History , a natural history encyclopedia by Pliny the Elder*Historia naturalis palmarum, a botanical book by Carl Friedrich Philipp von Martius published between 1823 and 1850...
, 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.Rendered fat...
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 is a historical name used in the context of the Roman Empire in references to the region of Western Europe approximating present day France and Belgium, but also sometimes including the Po Valley, western Switzerland, and the parts of the Netherlands and Germany on the west bank of the River...
s and Germans men are likelier to use it than women.
Another 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
ancient RomansAncient Rome was a civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC. Located along the Mediterranean Sea, it became one of the largest empires in the ancient world....
sacrificed animals. Rain would send a mix of animal tallow and
woodWood is an organic material; in the strict sense wood is produced as secondary xylem in the stems of trees . In a living tree it transfers water and nutrients to the leaves and other growing tissues, and has a support function, enabling woody plants to reach large sizes or to stand up for themselves...
ash down the mountain and into the clay soil on the banks of the
TiberThe Tiber is the third-longest river in Italy, rising in the Apennine mountains in Emilia-Romagna and flowing through Umbria and Lazio to the Tyrrhenian Sea. It drains a basin estimated at...
, producing a sudsy substance that could be used to clean clothes. The location of Mount Sapo is unknown, as is the source of the "ancient Roman legend" to which this tale is typically credited. In fact, the
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. Through the Roman conquest, Latin spread throughout the Mediterranean and a large part of Europe...
word
sapo simply means "soap"; it was borrowed from a Celtic or Germanic language, and is
cognateCognates in linguistics are words that have a common etymological origin.An example of cognates within the same language would be English shirt and skirt, the former from Old English scyrte, the latter loaned from Old Norse skyrta, both from the same Common Germanic *skurtjōn-. Words with this type...
with Latin
sebum, "tallow", which appears in Pliny the Elder's account. Roman animal
sacrificeSacrifice is commonly known as the practice of offering food, objects , or the lives of animals or people to the gods as an act of propitiation or worship...
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. Animal sacrifices in the ancient world would not have included enough fat to make much soap. The legend about Mount Sapo is probably apocryphal.
Zosimos of PanopolisZosimos of Panopolis was a Greek-Egyptian alchemist and Gnostic mystic from the end of the 3rd century and beginning of the 4th A.D., who was born in Panopolis, present day Akhmim in the South of Egypt, ca. 300. He wrote the oldest known books on alchemy, of which only quotations in the original...
c. 300 AD describes soap and soapmaking.
GalenAelius Galenus or Claudius Galenus , better known as Galen of Pergamum , was a prominent Greek physician and philosopher and probably the most accomplished medical researcher of the Roman period. His theories dominated and influenced Western medical science for well over a millennium...
describes soap-making using lye and prescribes washing to carry away impurities from the body and clothes. According to Galen, the best was German and ones from Gaul was 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 guilds 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 its origins in the Arnulfing and Pippinid clans of the 7th century. The name "Carolingian", Medieval Latin karolingi, an altered form of an unattested Old High German *karling, kerling The Carolingian dynasty (known variously as the...
capitulary
De Villis, dating to around 800, and sometimes attributed to
CharlemagneCharlemagne was King of the Franks from 768 to his death. He expanded the Frankish kingdoms into a Frankish Empire that incorporated much of Western and Central Europe...
, mentions soap as being one of the products the stewards of 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.
Soaps made from vegetable oils (such as olive oil), aromatic oils (such as
thymeThyme is a well known herb; in common usage the name may refer to* any or all members of the plant genus Thymus,* common thyme, Thymus vulgaris, and some other species that are used as culinary herbs or for medicinal purposes.-History:...
oil) and
lyeSodium hydroxide , also known as lye and caustic soda, is a caustic metallic base. It is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 1998 was around...
(
al-Soda al-Kawia) were first produced by chemists. From the beginning of the 7th century, soap was produced in
NablusNablus is a Palestinian city in the northern West Bank, approximately north of Jerusalem, with a population of 134,000...
(
West BankThe West Bank is a landlocked territory and is the eastern part of the Palestinian territories; on the west bank of the River Jordan in the Middle East. To the west, north, and south, the West Bank shares borders with the state of Israel, which maintains the security of this area. To the east,...
),
KufaKufa is a city in Iraq, about 170 km south of Baghdad, and 10 km northeast of Najaf. It is located on the banks of the Euphrates River. The estimated population in 2003 was 110,000....
(Iraq) and
BasraAl-Baṣrah is the capital of Basra Province, and had an estimated population of 3,800,200 as of 2009. Basra is also Iraq's main port, although it is incapable of deep water access, which is handled at the the port of Umm Qasr...
(
IraqIraq , officially the Republic of Iraq , also known as Mesopotamia, is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert.Iraq shares borders with Jordan to the west, Syria...
). Soap was perfumed and colored, some of the soaps were liquid and others were solid. They also had special soap for shaving. It was sold for 3 Dirhams (0.3 Dinars) a piece in 981 AD. The
PersianThe Persian people are the majority ethnic group in Iran. However, there are sub-groups who speak the Persian language as their mother tongue throughout the Iranian plateau. The term Persian has also a supra-ethnic significance and has been historically referred to a part of Iranian peoples...
chemist
Al-RaziAbū Bakr Muhammad ibn Zakariyā Rāzī , known as Rhazes or Rasis after medieval Latinists, was a Persian alchemist, chemist, physician, philosopher and scholar...
wrote a manuscript on recipes for true soap. A recently discovered manuscript from the 13th century details more recipes for soap making; e.g. take some sesame oil, a sprinkle of potash, alkali and some lime, mix them all together and boil. When cooked, they are poured into molds and left to set, leaving hard soap.
Modern history
Finer soaps were later produced in Europe from the 16th century, using vegetable oils (such as
olive oilOlive oil is a fruit oil obtained from the olive , a traditional tree crop of the Mediterranean Basin. The wild olive tree originated in Asia Minor and spread from there as far as southern Africa, Australia, Japan and China. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and...
) 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 soap made with olive oil originating from the Castile region of Spain.Importations of "Castile soap" through Antwerp appear in the London port books of 1567–68 , though the OED has no references to "Castile soap" earlier than 1616...
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 associated with the preservation of health and healthy living. Hygiene is a concept related to medicine, as well as to personal and professional care practices related to most aspects of living, although it is most often associated with cleanliness and...
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.
Commercial production
Until the
Industrial RevolutionThe Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, and transport had a profound effect on the socioeconomic and cultural conditions in the United Kingdom. The changes subsequently spread throughout Europe, North...
, soap-making was done 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
London[]London is the capital of England and the United Kingdom. It has been a major settlement for two millennia, and the history of London goes back to its founding by the Romans, when it was named Londinium. London's core, the ancient City of London, the 'square mile', retains its medieval boundaries...
. 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, affluent town of Saxon origin sited within the 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....
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 substances. The pestle is a heavy bat shaped stick whose end is used for pounding and grinding, and the mortar is a bowl, typically made of hard wood, marble, clay, or stone...
. William Hesketh Lever and his brother, James, bought a small soap works in
WarringtonWarrington is a large 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. The population of the borough of Warrington, including its 18 civil parishes, is around 194,000...
in 1885 and founded what is still one of the largest soap businesses, now called
UnileverUnilever is a multinational corporation, formed of British and Dutch parentage, 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 influence individuals to purchase products or services or support political candidates or ideas. Frequently it communicates a message that includes the name of the product or service and how that product or service could potentially benefit the consumer...
campaigns.
Soapmaking
The most popular soapmaking process today is the cold process method, where fats such as
olive oilOlive oil is a fruit oil obtained from the olive , a traditional tree crop of the Mediterranean Basin. The wild olive tree originated in Asia Minor and spread from there as far as southern Africa, Australia, Japan and China. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and...
react with
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...
, while some
soaperIn modern slang, a soaper is a person who practices soap making. It is the origin of the surnames "Soper," "Saboni," and "Soaper." Roads named "Sopers Lane," "Soper Street," and so forth are often so named because historically they were centres for soap making.Historically, in England and in the...
s use the historical hot process.
Handmade soap differs from industrial soap in that, usually, an excess of fat is sometimes used to consume the alkali (
superfatting), and in that the glycerin is not removed, leaving a naturally moisturising soap and not pure detergent. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap, though if too much fat is added, it can leave users with a "greasy" feel to their skin. Often,
emollientEmollients are substances that soften and soothe the skin. They are used to correct dryness and scaling of the skin. They are a key component in the manufacture of lipstick, lotions, and other cosmetic products....
s such as
jojobaJojoba , pronounced "hō-hō-bə", 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 core Caryophyllales. It is also known as goat nut, deer nut, pignut, wild hazel, quinine nut, coffeeberry, and...
oil or
shea butterShea butter or Shea nut butter is a slightly yellowish or ivory-colored natural fat extracted from fruit of the shea tree by crushing and boiling. Shea butter is widely used in cosmetics as a moisturizer and an emollient. Shea butter is also edible...
are added 'at trace' (the point at which the
saponificationSaponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid . Saponification is commonly used to refer to the reaction of a metallic alkali with a fat or oil to form soap. Saponifiable substances are those that can be converted into...
process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.
Lye
Reacting fat with NaOH will produce a stable soap that will usually become firmer as it cures.
Reacting fat with potassium hydroxide will produce a soap that is either soft or liquid. Historically, the alkali used was
potassium hydroxidePotassium hydroxide is an inorganic compound with the formula KOH. Along with sodium hydroxide, this colourless solid is a prototypical "strong base". It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive nature. In 2005, an...
made from the ashes of
brackenBrackens are a genus comprising several species of large, coarse ferns. 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 from
wood ashesWood ash is the residue powder left after the combustion of wood. Main producers of wood ash are wood industries and power plants.-Composition:...
.
Fat
Soap is derived from either vegetable or animal fats.
Sodium tallowateSodium tallowate is made from sodium hydroxide , steam, and animal fat . This process, called saponification, breaks down the triglyceride , frees the glycerol, and produces a sodium salt, called sodium tallowate...
, a common ingredient in many soaps, is derived from rendered beef fat. Soap can also be made of vegetable oils, such as
palm oilPalm oil is an edible plant oil derived from the pulp of the fruit of the oil palm Elaeis guineensis.Palm oil is naturally reddish because it contains a high amount of beta-carotene . Palm oil is one of the few vegetable oils relatively high in saturated fats...
, and the product is typically softer. If soap is made from pure
olive oilOlive oil is a fruit oil obtained from the olive , a traditional tree crop of the Mediterranean Basin. The wild olive tree originated in Asia Minor and spread from there as far as southern Africa, Australia, Japan and China. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and...
it may be called
Castile soapCastile soap is a name used in English-speaking countries for soap made with olive oil originating from the Castile region of Spain.Importations of "Castile soap" through Antwerp appear in the London port books of 1567–68 , though the OED has no references to "Castile soap" earlier than 1616...
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 recorded soapmaker in the area in about 1370...
. Castile is also sometimes applied to soaps with a mix of oils, but a high percentage of olive oil.
An array of saponifiable
oils and fatsVegetable fats and oils are lipid materials derived from plants. Physically, oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides, as contrasted with waxes which lack glycerin in their structure...
are used in the process such as olive, coconut, palm, cocoa butter,
hemp oilNot to be confused with honey oil or hash oilHempseed oil is pressed from the seed of the hemp plant irrespective of the strain of cannabis. However there is an extremely low or undetectable level of any psychoactive molecules in hemp seed oil as the seeds themselves do not contain psychoactive...
and shea butter to provide different qualities. For example, olive oil provides mildness in soap; coconut oil provides lots of lather; while coconut and palm oils provide hardness. Sometimes
castor oilCastor oil is a vegetable oil obtained from the castor bean . Castor oil is a colorless to very pale yellow liquid with mild or no odor or taste. Its boiling point is and its density is 961 kg·m−3...
can also be used as an ebullient. Most common, though, is a combination of coconut, palm, and olive oils.
Smaller amounts of
unsaponifiableUnsaponifiables are components of an oil, fat, wax, etc. that do not saponify. Unsaponifiables are important when creating a soap recipe in the process of soapmaking...
oils and fats that do not yield soap are sometimes added for further benefits.
Process
In both cold-process and hot-process soapmaking, heat may be required for
saponificationSaponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid . Saponification is commonly used to refer to the reaction of a metallic alkali with a fat or oil to form soap. Saponifiable substances are those that can be converted into...
.
Cold-process soapmaking takes place at a sufficient temperature to ensure the
liquificationMelting is a physical process that results in the phase change of a substance from a solid to a liquid. The internal energy of a solid substance is increased, typically by the application of heat or pressure, resulting in a rise of its temperature to the melting point, at which the rigid ordering...
of the fat being used. The lye and fat may be kept warm after mixing to ensure that the soap is completely saponified.
Unlike cold-processed soap, hot-processed soap can be used right away because lye and fat saponify more quickly at the higher temperatures used in hot-process soapmaking.
Hot-process soapmaking was used when the purity of lye was unreliable, and this process can use natural lye solutions, such as potash. The main benefit of hot processing is that the exact concentration of the lye solution does not need to be known to perform the process with adequate success.
Cold-process soapmaking requires exact measurements of lye and fat amounts and computing their ratio, using saponification charts to ensure that the finished product is mild and skin-friendly. Saponification charts can also be used in hot-process soapmaking, but are not as necessary as in cold-process soapmaking.
Hot process
In the hot-process method, lye and fat are boiled together at 80–100 °C until saponification occurs, which the soapmaker can determine by taste (the bright, distinctive taste of lye disappears once all the lye is saponified) or by eye (the experienced eye can tell when gel stage and full saponification have occurred).
After saponification has occurred, the soap is sometimes
precipitatedPrecipitation is the formation of a solid in a solution during a chemical reaction. When the reaction occurs, the solid formed is called the precipitate, and the liquid remaining above the solid is called the supernate...
from the solution by adding salt, and the excess liquid drained off.
The hot, soft soap is then spooned into a mold.
Cold process
A cold-process soapmaker first looks up the saponification value of the fats being used on a saponification chart, which is then 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% discount of lye so that all of the lye is reacted 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 both substances have cooled to approximately 100-110°F (37-43°C), and are no more than 10°F (~5.5°C) apart, they may be combined. This lye-fat mixture is stirred until "trace" (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 or ethereal oils, or simply as the "oil of" the plant from which they were extracted, such as oil of clove. An oil is "essential" in the sense that it...
s,
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, botanicals, herbs, oatmeal or other additives are 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 18 to 48 hours. Milk soaps are the exception. They do not require insulation. Insulation may cause the milk to burn. During this time, it is normal for the soap to go through a "gel phase" where the opaque soap will turn somewhat transparent for several hours, before once again turning opaque. The soap will continue to give off heat for many hours after trace.
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 complete. However, cold-process soaps are typically cured and hardened on a drying rack for 2-6 weeks (depending on initial water content) before use. If using caustic soda it is recommended that the soap is left to cure for at least four weeks.
Purification and finishing
The common process of purifying soap involves removal of
sodium chlorideSodium chloride, also known as salt, common salt, table salt, or halite, is an ionic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
,
sodium hydroxideSodium hydroxide , also known as lye and caustic soda, is a caustic metallic base. It is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 1998 was around...
, and
glycerolGlycerol is an organic compound, also commonly called glycerin or glycerine. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydrophilic hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. ...
. These components are removed by
boilingBoiling, a type of phase transition, is the rapid vaporization of a liquid, which typically 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...
the crude soap
curdCurds is 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 . Milk that has been left to sour will also naturally produce curds, and sour milk cheese is produced this way...
s in
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
and re-precipitating the soap with salt.
Most of the water is then removed from the soap. This was traditionally done on a chill roll 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. These pellets are now ready for soap finishing, the process of converting raw soap pellets into a salable 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 device for moving material or liquid by means of a rotating helical flighting. The material is moved along the axis of rotation. For some uses the helical 'flighting' is enclosed in a tube, for other uses the flighting is not encased...
, forces the soap through a fine
wireA wire is a single, usually cylindrical, string 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 wire gauges...
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, also known as cocoa liquor and cocoa mass, is a smooth liquid form of chocolate. Like the cocoa nibs 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 it passes through a vacuum chamber to remove any entrapped 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-Plurals:*Plural of:**Bar , a drinking establishment**Bar , a diacritical mark**Bar , a measure in music**Bar , or pressure*Dessert bars*Uneven bars, a gymnastics apparatus*The quality of the reception on a mobile phone...
are packaged in many ways.
SandSand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters. An individual particle in this range size is termed a sand grain...
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 the skin. Exfoliation is involved in the process of a facial and during body treatments at spas...
. Many newer materials are used for exfoliating soaps which are effective but do not have the sharp edges and pore size distribution of pumice.
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. Sometimes called the “space age metal”, it has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color.Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among other...
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. It is one of the four ferromagnetic elements at about room temperature, other three being iron, cobalt and gadolinium...
,
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
and
silverSilver is a 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 provide electron-robbing behavior when in contact with bacteria, stripping electrons from the organism's surface and thereby disrupting their functioning (typically killing the bacteria when it has lost too many electrons). 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.
Further reading
- Garzena, Patrizia - Tadiello, Marina (2004). Soap Naturally - Ingredients, methods and recipes for natural handmade soap. Programmer Publishing. ISBN 978-0-9756764-0-0.
External links