Episode 11: Soap's Secret Past: Guilds, Wars, and Chemistry | Dormant Knowledge Sleep Podcast

Host: Deb
Duration: ~96 minutes
Release Date: November 17, 2024
Episode Topics: Chemistry, Medieval History, Industrial History

Episode Summary

Prepare for a sudsy journey through 5,000 years of surprisingly dramatic soap history! In this episode of Dormant Knowledge, the educational sleep podcast for curious minds, Deb uncovers the hidden stories behind humanity's most essential cleaning invention. From ancient Babylonian clay tablets containing the first soap "recipes" to medieval guilds operating like protective tech companies, this episode reveals how soap has shaped civilization in unexpected ways.

Discover why the sophisticated Romans actually rejected soap in favor of oil and metal scrapers, how soap-making became entangled with wartime ammunition production, and why a simple chemical reaction discovered millennia ago proved crucial in fighting modern pandemics. We'll explore the molecular magic of saponification, meet the chemists who decoded soap's secrets, and understand why this everyday item was taxed as a luxury for over a century in England.

Whether you're fascinated by chemistry, intrigued by medieval craft guilds, or simply curious about the science behind getting clean, this episode offers a perfect blend of historical intrigue and scientific discovery, all delivered in Deb's signature conversational style that's engaging enough to capture your attention yet gentle enough to guide you toward restful sleep.

What You'll Learn

• Discover the ancient origins of soap-making from Babylonian tablets dating to 2800 BCE and why we still don't know who truly "invented" soap
• Explore medieval soap guilds and their closely guarded trade secrets that operated like modern intellectual property protection
• Learn the chemistry of saponification and how soap molecules perform their cleaning magic at a molecular level
• Uncover soap's surprising role in WWI when glycerin became more valuable for explosives than for cleaning
• Understand why soap was taxed as a luxury item in England for 141 years and how this affected public health
• Meet the pioneering chemists like Michel Eugène Chevreul who finally explained how soap actually works
• Trace the industrial revolution's impact on soap production and how it transformed from luxury to necessity
• Connect modern craft soap movements to ancient traditions and contemporary environmental concerns

Episode Transcript

Dormant Knowledge: The Art and Science of Soap
Full Episode Script
[Soft ambient music fades in]
Deb: Welcome to Dormant Knowledge. I'm your host, Deb, and this is the podcast where you'll learn something fascinating while gently drifting off to sleep. Our goal is simple: to share interesting stories and ideas in a way that's engaging enough to capture your attention, but delivered at a pace that helps your mind relax and unwind. Whether you make it to the end or drift away somewhere in the middle, you'll hopefully absorb some knowledge along the way.
We really enjoy working on this project and would love to continue with your support. You can find us at dormantknowledge.com or follow us on social media @dormantknowledge on Instagram and Facebook, or @drmnt_knowledge—that's d-r-m-n-t-underscore-knowledge—on X. And if you'd like to support the show, you can buy us a coffee at BuyMeACoffee.com/@DormantKnowledgePodcast.
Tonight, we're exploring something you probably used this morning without giving it a second thought... soap. [soft chuckle] I know, I know, it sounds almost too mundane to be interesting, but, um, bear with me here. The story of soap is actually this fascinating intersection of ancient mystery, medieval craft, modern chemistry, and... well, explosive history. Literally. We'll get to that.
So settle in, get comfortable, and let's begin our journey into the surprisingly complex world of soap.
[Music fades out]

You know, every single day, probably multiple times a day, you use this substance that's been around for thousands of years. And yet... [pause] ...if I asked you to explain how soap actually works, really works, you might struggle a bit. I mean, we all know it cleans things, obviously, but why does it clean? What's happening at a molecular level when you wash your hands?
And then there's the history. Soap has been part of human civilization for so long that we're not even entirely sure who invented it. The ancient Babylonians? The Egyptians? Some unknown culture that left no written records? It's one of those inventions that feels so fundamental that it's hard to imagine a time before it existed.
But tonight, we're going to unpack all of that. The chemistry, yes—because understanding saponification, that's the technical term for soap-making, is actually pretty satisfying once you get into it. But also the human stories. The medieval soap guilds with their closely guarded secrets. The taxes that made soap a luxury item for centuries. The moment during World War I when soap became a military necessity... not for cleaning, but for making explosives.
[sound of settling into chair]
Let's start at the beginning, or at least, as close to the beginning as we can get.

Ancient Origins & Early History
So, the oldest written record we have that mentions soap—or something very much like soap—comes from ancient Babylon, around 2800 BCE. That's, um... [small laugh] ...that's a really long time ago. We're talking about clay tablets with cuneiform writing that describe a substance made from boiling fats with ashes.
Now, these tablets don't explicitly say, "This is for washing your hands" or anything like that. They're more like... recipes? Instructions? The exact purpose isn't entirely clear, which is, you know, frustratingly typical of ancient texts. But the chemical process described is definitely saponification. They were making soap, whether they fully understood what they were making or not.
[pause, sound of paper shuffling]
There's this famous legend—you might have heard it—about Mount Sapo. The story goes that there was a mountain near Rome where animals were sacrificed, and the animal fat would mix with wood ashes from the sacrificial fires, and rain would wash this mixture down into the clay soil by the Tiber River. And the women washing clothes in the river noticed that their clothes got cleaner in these particular spots where this mixture had washed down.
It's a great story. Very... poetic. The problem is, um, there's no Mount Sapo. Or at least, no one's ever found convincing evidence of it. The story might be a later invention to explain the word "soap" itself—which might come from the Latin "sapo," or maybe from a Germanic root, or... [trails off] ...honestly, etymology gets complicated.
But here's what we do know: the ancient Egyptians were using something soap-like. They had these pastes made from vegetable oils and animal fats combined with alkaline salts—they used something called natron, which is a naturally occurring mixture of sodium carbonate and sodium bicarbonate. They found deposits of it in dried lake beds.
The Egyptians used these mixtures for bathing, but also, interestingly, for preparing wool for weaving. And for medicinal purposes. The Ebers Papyrus, which dates to around 1550 BCE, has recipes for these preparations.
[soft yawn]
Now, here's where it gets interesting from a historical detective perspective. We have evidence of soap-like substances from multiple ancient civilizations—Babylon, Egypt, ancient Rome, early Germanic tribes—but we don't have a clear "inventor." It's one of those technologies that seems to have been discovered and rediscovered, developed independently in different places.
The Romans, for instance, they're famous for their baths, their thermae, these elaborate bathing complexes. But they didn't primarily use soap. They had this practice where they'd coat their skin with oil, then scrape it off with a curved metal tool called a strigil. The oil would take the dirt with it. Soap was known, but it was... well, it was kind of a barbarian thing. The Germanic tribes used it, the Gauls used it. The sophisticated Romans? They had their oils and their strigils.
But here's the thing—and this is a pattern we'll see throughout history—different regions developed different types of soap based on what they had available. In the Mediterranean, where olive oil was abundant, you'd get these soft, paste-like soaps. In northern Europe, where animal fats were more common, they'd make harder soaps. And the alkali source varied too. Wood ashes, sure, but also certain plants, seaweed... whatever worked.
[pause]
So by the time we get to, say, the early medieval period, soap is known throughout Europe and the Mediterranean. But it's not... it's not what we'd call a common household item. It's still relatively expensive to make, and most people? They're using other methods. Water and scrubbing. Sand. Vinegar. Whatever's available and cheap.
But that's about to change. Well... eventually it'll change. First, we have to go through a few centuries of soap guilds and soap taxes.

Medieval Soap & The Guild Era
[sound of shifting in chair]
Okay, so, um, during the medieval period, soap production becomes this really strange intersection of craft, commerce, and... well, let's call it industrial espionage. [soft chuckle]
The Islamic Golden Age—roughly the 8th to the 14th centuries—saw some major advances in soap-making. Muslim chemists figured out how to make soap using vegetable oils instead of just animal fats. They perfected the use of sodium hydroxide—lye—which gave you a harder, longer-lasting soap. And they added fragrances. Perfumed soaps became a specialty of cities like Aleppo in Syria and, um, Damascus, Cairo...
These weren't just functional items anymore. These were luxury goods. Desirable trade items.
And then this knowledge spreads to Europe, particularly through Spain during the period of Al-Andalus, and through trade routes to Venice and other Mediterranean ports. And by the later medieval period, you start seeing these specialized soap-making centers develop.
Marseille in France becomes famous for its soap—Savon de Marseille. [pronunciation: sah-VON duh mar-SAY] Castile in Spain has Castile soap, made from olive oil. Venice, of course, the great trading city, produces soap. These aren't just random craftspeople making soap in their backyards. These are organized industries.
[pause]
And like many medieval industries, soap-making becomes controlled by guilds. These professional organizations that regulated who could make soap, how it should be made, what could go into it... The guilds protected trade secrets. If you were a master soap-maker in a guild, you'd have apprentices, and you'd teach them the craft, but you'd also make sure those secrets didn't spread to competing cities.
There were genuine innovations happening, but they were closely guarded. The exact proportions of oils and lye, the timing of the heating process, additives that would make the soap harder or softer or give it particular properties... this was valuable knowledge.
But here's where things get really interesting: governments noticed that people would pay good money for soap. And where there's money, there's... [slight laugh] ...taxation.
England imposed a soap tax in 1712. It was pretty hefty—several pence per pound, which doesn't sound like much, but when you're talking about a basic hygiene product, it adds up. The tax lasted until 1853. That's over 140 years. Similar taxes existed in France and other European countries.
The effect of these taxes was to keep soap as a luxury item. The wealthy could afford fine, perfumed soaps. The working classes? They made do with whatever they could get, which often meant very basic, harsh soaps, or just... not using soap much at all.
There's this phrase in English, "the great unwashed," which referred to the lower classes in the 18th and 19th centuries. And, you know, there's this popular image of medieval and early modern Europe as being incredibly dirty, but the reality is more complicated. People did wash. They valued cleanliness. But soap was expensive because of these taxes and because production was still relatively labor-intensive.
[sound of drinking water]
Different regions had different specialties based on what oils and fats were available. Hard soap versus soft soap was a major distinction. Hard soap, made with sodium hydroxide and typically using animal fats or specific vegetable oils, would form into bars that you could store and use over time. Soft soap, made with potassium hydroxide and often using lower-quality oils, stayed... well, soft. More like a paste or jelly. It was cheaper to make but harder to store and transport.
So you'd have households making their own soft soap from kitchen waste fats and wood ashes. But the fine hard soaps? Those were commercial products, guild-produced, taxed...
And owning nice soap became a bit of a status symbol. If you had money, you might have French soap scented with lavender. Or Spanish Castile soap. These were markers of wealth and refinement.
It's fascinating how something as basic as soap could become tangled up in economics and social class and international trade. But that's about to get even more interesting when chemistry becomes a real science rather than a craft tradition.
[pause]
And actually, understanding what's actually happening during soap-making—the chemistry of it—that's where things get really satisfying. So let's talk about saponification.

The Chemistry Unveiled - Saponification
[Soft ambient music begins to fade in]
Deb: I'm going to take a quick break here. When we come back, we'll dive into the actual chemistry of how soap works—which, I promise, is less intimidating than it sounds.
[Music plays for transition]
Deb: Welcome back to Dormant Knowledge...
[Music fades out]
So, saponification. [pronunciation: sah-pon-ih-fih-KAY-shun] It's one of those wonderful chemistry words that sounds more complicated than the concept actually is. The word comes from the Latin "sapo," meaning soap, and basically, it just means "soap-making." But the process itself? That's where things get interesting.
At its most basic, soap is the result of a chemical reaction between fats or oils and an alkali. That's it. Two categories of ingredients: something fatty, and something alkaline. Mix them under the right conditions, and you get soap.
[pause]
Let's break down what's actually happening here. Fats and oils are made up of molecules called triglycerides. [pronunciation: try-GLISS-er-ides] These are basically three fatty acid chains attached to a glycerol backbone. Think of it like... um, a capital E shape, where the vertical line is the glycerol and the three horizontal lines are fatty acids.
When you add an alkali—typically lye, which is sodium hydroxide or potassium hydroxide—something interesting happens. The lye breaks those bonds between the glycerol and the fatty acids. It's called hydrolysis. The triglyceride molecule splits apart.
What you end up with are two products: free fatty acids that have reacted with the alkali to form soap molecules, and free glycerol—also called glycerin—as a byproduct.
[soft chuckle]
The glycerin thing is actually historically important, which we'll get to later, but for now, just know that it's this sweet, syrupy liquid that's really useful for all kinds of things.
But the soap molecules themselves—those are the fascinating part. Each soap molecule has two ends with very different properties. One end—the fatty acid end—is hydrophobic, meaning it repels water but attracts oils and fats. The other end—the end that's bound to the sodium or potassium from the lye—is hydrophilic, meaning it loves water.
This dual nature is why soap works. When you wash your hands with soap, these molecules arrange themselves around tiny droplets of oil and dirt. The hydrophobic ends stick into the oil, and the hydrophilic ends face outward toward the water. This creates these little structures called micelles. [pronunciation: my-SELLS]
[pause, considering]
Imagine... okay, imagine a bunch of people forming a circle, all facing outward, arms linked. In the center of the circle, there's something—let's say a ball. The people are the soap molecules, their arms facing outward are the water-loving ends, and the ball in the middle is a droplet of oil or dirt. That's essentially a micelle.
When you rinse with water, these micelles get washed away, taking the dirt and oil with them. That's how soap cleans. It's not magic—though, you know, before people understood this chemistry, it might as well have been magic. You mix ash and fat, and somehow you get this substance that makes things clean? That must have seemed pretty miraculous.
The type of fat or oil you use affects the properties of the soap. Coconut oil makes a soap that lathers really well but can be drying. Olive oil makes a very gentle, moisturizing soap but doesn't lather as much. Animal fats—tallow from beef or lard from pigs—make hard, long-lasting bars. Palm oil is in between.
And the alkali matters too. Sodium hydroxide gives you hard bar soap. Potassium hydroxide gives you soft or liquid soap. Both are pretty caustic chemicals—you do not want to get lye on your skin—but in the finished soap, if you've done the reaction correctly, all the lye has reacted. It's been converted into soap. The finished product isn't caustic at all.
[soft yawn]
There's an art to getting the proportions right. Too much lye, and you get harsh soap that might still have free alkali in it. Too little lye, and not all the fats convert—you get oily, soft soap that doesn't clean as well. The exact ratios depend on the specific fats you're using, because different fats have different numbers and types of fatty acids.
For centuries, this was done by experience and tradition. Soap makers would know—just know, from practice—how much ash water to add to a particular type of fat. They'd test it, adjust it, develop a feel for it.
But in the 18th and early 19th centuries, as chemistry became more rigorous, people started understanding this process at a molecular level. And that understanding led to the industrial revolution in soap making.

Industrial Revolution & Mass Production
The big breakthrough for industrial soap production came from... [pause] ...well, actually, it came from trying to solve a different problem entirely.
In 1791, a French chemist named Nicolas Leblanc [pronunciation: nick-oh-LAH luh-BLAHNK] developed a process for making soda ash—sodium carbonate—from common salt. This was huge for a lot of industries, but for soap makers, it meant they could produce alkali cheaply and consistently, instead of relying on wood ashes or other natural sources.
Then, in 1823, another French chemist, Michel Eugène Chevreul [pronunciation: mee-SHEL oo-ZHEN shev-ROIL], published research that explained the chemical nature of fats and the saponification process. He figured out that fats were composed of glycerin and fatty acids. This wasn't just theoretical—it gave soap makers a scientific basis for understanding their craft.
[sound of papers shuffling]
But the really transformative moment, at least in England, came in 1853 when they repealed the soap tax. Suddenly, soap could be produced and sold cheaply. And just at the right time, too, because the Industrial Revolution was creating large urban populations who needed access to affordable hygiene products.
Companies like Lever Brothers in England and Procter & Gamble in America became major soap manufacturers. These weren't small operations. These were factories producing soap on a scale that would have been unimaginable a century earlier.
Procter & Gamble—which started in Cincinnati in 1837—accidentally created one of the most successful soap brands ever. In 1879, a worker left a soap-making machine running during lunch break, and extra air got whipped into the batch. The result was a soap that floated in water. They called it Ivory Soap and marketed it with the slogan "It floats!" [slight laugh]
Sometimes the best innovations are complete accidents.
But soap companies weren't just making soap—they were inventing modern advertising. Pears' Soap in England hired artists to create these beautiful advertisements. They bought the rights to famous paintings and used them in their marketing. They created brand identity, brand loyalty.
And they also tied soap to these broader social movements. The Victorian obsession with cleanliness and morality—"Cleanliness is next to godliness"—that became a marketing angle. Public health campaigns in cities promoted handwashing and bathing as ways to prevent disease. Soap companies were more than happy to support these campaigns.
[pause]
The late 1800s and early 1900s saw soap production become increasingly sophisticated. Continuous process manufacturing replaced batch production in many factories. Instead of making one batch of soap at a time, you had this continuous flow—fats in one end, finished soap out the other.
But then came World War I, and soap became important for a completely different reason: glycerin.
Remember that byproduct I mentioned earlier? Glycerin? Well, it turns out glycerin is a key ingredient in making nitroglycerin, which is used in explosives. During WWI, glycerin became a critical military resource. Soap factories were essentially munitions suppliers.
The same thing happened during World War II. Soap was rationed in many countries, not just because fats were needed for food, but because glycerin was needed for the war effort. Soap companies had to reformulate their products, find substitutes, work with whatever fats were available.
[sound of shifting in chair]
After the wars, soap production ramped back up, but the industry was about to face a new challenge: synthetic detergents. But before we get to that, let's talk about what a modern soap factory actually looks like.

Modern Manufacturing Process
So, industrial soap making today is... it's pretty impressive, actually. If you've ever toured a factory—any kind of factory—there's something almost hypnotic about watching raw materials get transformed into finished products.
Modern soap manufacturing typically uses what's called the continuous process. Fats and oils—these might be palm oil, coconut oil, tallow, whatever the specific formula requires—get pumped into a tall column called a hydrolyzer. [pause] In the hydrolyzer, the fats are split apart using high temperature and pressure. This separates the fatty acids from the glycerin.
The glycerin gets drawn off—it's valuable stuff, used in cosmetics, pharmaceuticals, food products, even as a solvent. It's not wasted.
The fatty acids then go to a neutralization process where they're combined with the alkali—sodium hydroxide for hard soap. This is the actual saponification happening, but at industrial scale. The reaction is carefully controlled, temperature monitored, everything precise.
What comes out is this thick, viscous soap mass. It's not bars yet. It's more like... [pause, considering] ...like very thick, opaque honey. This crude soap still has impurities and excess water.
So it goes through a purification stage. Sometimes they'll add salt, which causes the soap to separate from any remaining water and glycerin. The soap floats to the top—it's less dense—and can be skimmed off. This is called "salting out."
[soft laugh]
Then comes something called milling and plodding. The soap gets passed through rollers that compress it, remove any remaining air bubbles, and create a smooth, homogeneous texture. This is especially important for bar soap—you want consistency.
At this stage, additives get mixed in. Fragrances, colors, sometimes antibacterial agents, moisturizers, whatever the specific product requires. These get thoroughly blended into the soap mass.
Then the soap goes through an extruder—basically a machine that pushes the soap through a shaped opening. For bar soap, this creates a continuous log of soap that gets cut into individual bars. These bars might get stamped with a brand logo or design.
Finally, the bars are packaged and shipped.
The whole process, from fats going in to finished bars coming out, can happen in less than a day in a modern factory. Compare that to traditional cold-process soap making, where you might wait weeks for the soap to cure properly... it's a completely different scale.
[pause]
But here's an interesting tension in the modern soap industry: efficiency versus quality. Industrial soap production is incredibly efficient. It's cheap, consistent, fast. But in the process of removing the glycerin—which factories sell separately because it's valuable—you're taking out one of the things that makes soap gentle on skin.
Commercial bar soaps often have to add moisturizers back in to compensate. And many people feel that the old-fashioned, glycerin-rich soaps made in small batches are better for your skin.
But then, you know, those traditional soaps cost more. A lot more. So you've got this interesting market split between mass-produced commodity soap and artisan craft soap. We'll come back to that later.
[sound of drinking water]
First, though, we need to talk about something that really transformed cleaning in the 20th century: synthetic detergents. Because here's the thing—technically speaking, most of what we call "soap" today isn't actually soap at all.

Soap vs. Detergent - The Modern Distinction
Okay, so... [pause] ...this is one of those things where the common language and the technical language diverge pretty sharply.
When most people say "soap," they mean any cleaning product. Hand soap, dish soap, laundry soap... But chemically speaking, true soap is specifically the product of saponification—fats reacted with alkali. And true soap has some limitations.
The biggest problem is hard water. Water with high mineral content—specifically calcium and magnesium ions. When you use real soap in hard water, those minerals react with the soap to form what's called soap scum. You've seen this—it's that grimy film that builds up in showers and sinks. It's literally insoluble compounds formed between the soap and the minerals.
This doesn't just look bad. It means your soap is less effective. Those soap molecules are getting bound up with minerals instead of cleaning.
[soft sigh]
During World War I, Germany faced a shortage of fats for soap making—everything was going to food production. So German chemists developed synthetic alternatives—chemical compounds that could clean like soap but weren't made from fats and oils. These were the first synthetic detergents.
After the war, development continued, but slowly. It wasn't until after World War II that synthetic detergents really took off, especially in the United States.
In 1946, Procter & Gamble introduced Tide. This was a revolutionary product—a heavy-duty synthetic detergent specifically designed for washing machines and hard water. It was, um... [chuckle] ...it was incredibly successful. Within a few years, synthetic detergents had largely replaced soap for laundry.
The chemistry is different. Synthetic detergents—technically called syndets [pronunciation: SIN-dets]—are usually made from petroleum products. They're long-chain molecules with similar properties to soap—one end loves water, one end loves oil—but their chemical structure makes them immune to hard water problems. They don't form scum.
They also wash out of fabrics more easily, they work in cold water, they're more versatile... From a practical standpoint, for most cleaning applications, synthetic detergents are superior to true soap.
[pause]
But there's a trade-off, right? There's always a trade-off.
Early synthetic detergents contained phosphates—these helped soften water and boost cleaning power. But phosphates in waterways cause massive algae blooms, which deplete oxygen and kill fish. By the 1960s and 70s, water pollution from detergents was a major environmental issue. Regulations forced manufacturers to reformulate.
Modern detergents use different water softeners and cleaning agents. But there are still concerns. Sulfates—like sodium lauryl sulfate or sodium laureth sulfate—are common in shampoos and body washes. They create lather and clean effectively, but some people find them irritating to skin. There's ongoing debate about various synthetic ingredients, parabens, phthalates...
Meanwhile, true soap—old-fashioned saponified soap—is biodegradable, made from renewable resources, and generally gentler on skin. But it doesn't work as well for laundry, doesn't perform well in hard water, and can be drying if not properly formulated.
[sound of shifting]
So what do you do? Well, manufacturers have gotten creative. "Soap-free cleansers" or "syndet bars" combine the mildness of soap with some of the benefits of synthetic detergents. These use gentle synthetic surfactants—that's the technical term, surfactants, for molecules that clean by reducing surface tension—but avoid harsh sulfates.
You'll see products labeled "for sensitive skin" or "dermatologist tested"—often these are syndet formulations designed to be less irritating than both traditional soap and harsh detergents.
It's become a whole... [slight laugh] ...it's become a whole complicated landscape of products and formulations and marketing claims. Which brings us, actually, to an interesting counter-movement: the revival of traditional, handmade, small-batch soap.

[Soft ambient music begins to fade in]
Deb: I'm going to take another quick break here. When we come back, we'll talk about the craft soap movement and why people are making soap the old-fashioned way.
[Music plays for transition]
Deb: That music almost put me to sleep! But if you're still with me, welcome back to Dormant Knowledge...
[Music fades out]

The Artisan Revival - Handmade & Craft Soaps
So there's this interesting thing that's happened over the past couple decades. As industrial products have become more standardized, more synthetic, more... anonymous, I guess... there's been this counter-movement toward handmade, artisan goods. You see it with bread, with beer, with furniture... and definitely with soap.
Craft soap making—people making soap in small batches using traditional methods—has become surprisingly popular. You can find these soaps at farmers' markets, on Etsy, in boutique shops... And the people making them range from hobbyists who started making soap for themselves and friends, to serious small businesses producing hundreds of bars a week.
[pause]
The most common method for craft soap making is called cold process. This is traditional saponification—mixing fats with lye—but done at relatively low temperatures and without the industrial separation of glycerin.
Here's the basic process: You'd start by carefully measuring your oils and fats. Maybe olive oil, coconut oil, shea butter, whatever recipe you're following. You melt those together if needed, get them to the right temperature—usually around 100 to 110 degrees Fahrenheit.
Separately, you mix lye—sodium hydroxide—with water. This is... [pause] ...this is the dangerous part. Lye is caustic. It will burn skin. When you mix lye with water, the solution heats up dramatically. You have to be very careful. Protective eyewear, gloves, good ventilation...
Once both the oils and the lye solution are at the right temperature, you combine them. Then you stir—often using a stick blender to speed things up—until the mixture reaches "trace." That's when the soap has emulsified and thickened enough that if you drizzle some across the surface, it leaves a trace, a visible trail, before sinking back in.
At trace, you can add your fragrance oils or essential oils, any colorants, additional ingredients like oatmeal or clay or dried flowers... Then you pour the mixture into molds.
[soft yawn]
And then... you wait. The soap continues to saponify in the molds. It heats up from the reaction—that's called the gel phase. After 24 to 48 hours, it's solid enough to unmold and cut into bars.
But it's not ready to use yet. The soap needs to cure. During curing, excess water evaporates and the saponification process completes fully. Most soap makers cure their soap for four to six weeks. You can use it sooner, but it'll be softer and won't last as long.
There's a variation called hot process, where you actually cook the soap mixture—usually in a slow cooker—to speed up saponification. Hot process soap is technically ready to use right away, though it still benefits from some drying time. The texture is different though—it's usually more rustic, less smooth.
[pause]
One thing craft soap makers often do is something called superfatting. This means using slightly less lye than needed to completely saponify all the oils. The result is soap with some free oils left in it—oils that haven't been converted to soap. These leftover oils are moisturizing. They make the soap gentler on skin.
Commercial soap manufacturers remove the glycerin and sell it separately. Craft soap makers leave the glycerin in. Between the superfatting and the glycerin content, handmade soap tends to be much more moisturizing than commercial soap.
The choice of oils matters a lot. Coconut oil creates great lather but can be drying if used alone. Olive oil is gentle but doesn't lather much. Shea butter adds creaminess. Castor oil stabilizes lather. Most recipes use a blend of oils to get balanced properties.
And then there are all the additives. Essential oils for scent—lavender, peppermint, eucalyptus, tea tree... Natural colorants like clays or plant powders. Exfoliants like oatmeal or coffee grounds or poppy seeds. Milk or honey for extra richness.
[soft chuckle]
It's become quite an art form. If you browse craft soap offerings, you'll find incredible variety. Swirled colors, layered designs, embedded decorations... It's functional art, really.
But there are also regulations. In the United States, if you're selling soap, it has to meet certain criteria. True soap—the saponified product—can be sold as soap without special labeling, as long as you're not making specific health claims. But if you add certain ingredients or make claims about treating skin conditions, suddenly your product might be classified as a cosmetic or even a drug, which comes with much stricter FDA regulations.
Most craft soap makers are careful about this. They'll say their soap is "gentle" or "moisturizing" but won't claim it treats eczema or acne, because that would trigger additional regulatory requirements.
[pause]
Why do people make their own soap? I mean, you can buy soap anywhere, it's cheap, it's convenient... But people who get into soap making often talk about control and quality. Knowing exactly what's in their soap. Being able to avoid synthetic fragrances or certain ingredients. Creating products customized for their own skin type.
There's also something satisfying about the craft itself. Taking these basic raw materials—oils, lye, water—and creating something useful and beautiful. It's old-fashioned chemistry. It's hands-on and tangible in a way that a lot of modern life isn't.
And for some people, it becomes a business. Not a huge business, usually—the soap market is competitive, and margins are tight—but a viable small business. Selling at local markets, through Etsy, to boutique stores...
The craft soap movement is part of this broader trend toward knowing where things come from, supporting small producers, valuing quality over convenience. It's interesting how soap, this ancient technology, has found new relevance in the 21st century.
But of course, craft soap isn't the only type of specialty soap out there. Different cultures have their own traditional soap-making techniques, some going back centuries.

Specialty Soaps & Cultural Variations
You know, one of the things I find fascinating about soap history is how different regions developed their own distinctive styles based on local materials and traditions. Some of these have become, um, almost legendary in soap-making circles.
[pause]
Take Castile soap. This originally came from the Castile region of Spain—hence the name—and it's traditionally made with 100% olive oil. No other fats, just olive oil and lye. The result is a very mild, gentle soap that's, well, it's not great for lather, but it's wonderful for sensitive skin.
Real Castile soap takes a long time to cure—sometimes several months—because olive oil soap stays soft for quite a while. But once it's properly cured, it's very hard and long-lasting. It's also... [slight laugh] ...it's also kind of slimy when wet? That's the olive oil. Some people love it, some people find it off-putting.
Modern "Castile soap" products, like Dr. Bronner's, which you've probably seen—those are actually Castile-style soaps made with a blend of oils, not pure olive oil. They're more liquid soap formulations. Still very gentle, but not quite the same as traditional Spanish Castile soap.
Then there's Marseille soap—Savon de Marseille. [pronunciation: sah-VON duh mar-SAY] This French soap has been made in Marseille since at least the 1370s. Traditional Marseille soap is made from sea water, olive oil, and soda ash from sea plants. It has to be made in a specific way, using large cauldrons, with multiple washing and purification stages.
Authentic Marseille soap comes in these big cubes—usually green or white—stamped with "72% oil" which indicates the purity. It's been used for everything from laundry to bathing to washing dishes. Very simple, very functional, very long-lasting.
[sound of settling]
Aleppo soap from Syria is even older—possibly the world's oldest soap still being made. Aleppo soap is made from olive oil and laurel berry oil. The laurel oil is what makes it special—it has this distinctive, earthy smell and is traditionally valued for skin conditions.
The making of Aleppo soap is seasonal. The soap is made in the winter, then stored in towers to cure for six to nine months. Traditional Aleppo soap is brown on the outside from oxidation, but when you cut into it, it's green inside from the laurel oil.
Unfortunately, the Syrian civil war has devastated the Aleppo soap industry. Many of the ancient soap factories have been destroyed. Some soap makers have fled and are trying to continue the tradition in exile, but... [trails off] ...it's a reminder that these craft traditions are fragile.
African black soap is another traditional type. It's made in West Africa—Ghana, Nigeria, other countries in the region—from plantain skins or cocoa pods that are sun-dried and then roasted. The ashes from these are mixed with palm oil or coconut oil and water.
The result is a soap that's actually brown, not black, despite the name, and it has this soft, almost crumbly texture. It's quite alkaline, so it can be drying for some people, but it's traditionally used for all kinds of skin issues. It's become pretty popular internationally in recent years.
[pause]
Japan has its own traditions too. Japanese camellia oil soap—made from tsubaki oil—has been used for centuries, especially for hair care. The oil comes from camellia seeds, and it's prized for making hair shiny and manageable.
And then there are the medicinal soaps. Sulfur soap, which has been used for centuries for various skin conditions. Coal tar soap, which sounds... [chuckle] ...which sounds pretty unappealing, but was used historically for psoriasis and eczema. These days, there are endless specialty soaps claiming various benefits—antibacterial soaps, exfoliating soaps, moisturizing soaps...
Speaking of antibacterial soaps, that's actually become controversial. For years, antibacterial soaps were marketed as being more hygienic, more effective. They contained triclosan or other antibacterial agents. But research has shown that for normal household use, antibacterial soap isn't more effective than regular soap and water. And there are concerns about contributing to antibiotic resistance.
The FDA actually banned certain antibacterial agents from consumer soaps in 2016. Plain soap works just fine for most purposes. The mechanical action of washing—the rubbing, the water flow—that's what removes most germs anyway.
[soft yawn]
There's also the whole question of bar soap versus liquid soap. Liquid soap is technically still soap—it's usually made with potassium hydroxide instead of sodium hydroxide, which creates a soap that stays liquid. But many "liquid soaps" are actually synthetic detergent formulations.
The advantage of liquid soap is convenience and hygiene—there's no shared bar that everyone touches. The disadvantage is packaging—all those plastic bottles—and cost. Liquid soap is usually more expensive per use than bar soap.
Some people have gotten creative with this. Soap flakes or soap sheets—thin pieces of soap that dissolve in water—for travel. Refillable liquid soap dispensers to reduce plastic waste. The humble bar of soap being reimagined for modern concerns.
But regardless of format or type, the basic principle is the same. Soap works because of its molecular structure, because of that clever trick of having one end that attracts oil and one end that attracts water. Everything else—the scent, the texture, the special ingredients—that's all variation on the theme.

Soap in Modern Life & Future
[sound of shifting in chair]
So here we are in 2025, and soap is... well, it's everywhere. It's so ubiquitous that we barely think about it. But the past few years have actually brought soap back to public consciousness in a pretty dramatic way.
The COVID-19 pandemic, which started in 2020, made handwashing one of the most important public health measures. Suddenly, everyone was very aware of proper handwashing technique. Twenty seconds, all surfaces of the hands, soap and water...
And here's the thing: soap works against viruses, including coronaviruses. Not because it's antibacterial—it's not, or at least not primarily—but because viruses are surrounded by lipid envelopes. That fatty layer. And soap, being designed to break up fats, breaks up those viral envelopes. It literally pulls viruses apart at a molecular level.
[pause]
So that simple technology—fat plus lye equals soap—that technology that's been around for thousands of years, turned out to be one of our best defenses against a modern pandemic. That's... that's kind of amazing when you think about it.
But soap production and use also raise environmental questions. Palm oil, which is widely used in soap making, is associated with deforestation in Southeast Asia. Orangutan habitats being destroyed for palm plantations. It's become a real concern for environmentally conscious consumers.
Some soap makers have switched to sustainable palm oil—certified by organizations like the RSPO—or to other oils entirely. But it's complicated. Palm oil is incredibly efficient per acre compared to other oil crops, so replacing it entirely might actually require more land, not less.
Then there's the packaging issue. All those plastic bottles for liquid soap and body wash. Some companies are experimenting with solid shampoo bars and body bars—essentially a return to bar soap format—to reduce plastic waste. It's one of those interesting moments where the old-fashioned option becomes the environmentally progressive choice.
There's also the question of what happens to soap after it goes down the drain. True soap is biodegradable—it breaks down relatively quickly. Synthetic detergents vary. Some break down easily, some are more persistent. And all the other ingredients—fragrances, colors, preservatives—those can accumulate in water systems.
For people with septic systems or gray water systems, the type of soap you use actually matters. Some soaps and detergents can disrupt the bacterial balance in septic tanks. Others are better. It's something that, you know, most people never think about until they have to.
[pause]
Looking forward, there are some interesting innovations in development. Probiotic soaps that contain beneficial bacteria to support the skin's microbiome—the community of microorganisms that naturally live on our skin. The idea is that killing all bacteria might not be ideal; maybe we should be supporting the good bacteria instead.
There's research into waterless soap alternatives—foams or wipes that could clean effectively without requiring water. This could be huge for water-scarce regions or emergency situations.
Some companies are working on soap formulations using synthetic biology—engineering microorganisms to produce specific oils or compounds. It's very cutting-edge, very science-fiction-y, but also kind of a continuation of the same process humans have been doing for millennia: figuring out the best way to make soap.
And there's renewed interest in understanding the traditional knowledge of soap making. Not just as nostalgia, but as potentially useful information. Traditional soaps often used local, sustainable ingredients. They were biodegradable by default. Maybe there are lessons there for modern formulation.
[soft chuckle]
It's funny, isn't it? Soap seems like such a simple, solved problem. We figured this out thousands of years ago. Mix fat with lye, get soap, done. But there are still questions, still innovations, still trade-offs between cost and quality, between industrial efficiency and environmental impact, between convenience and sustainability.
The chemistry is well understood now. We know exactly how saponification works at a molecular level. We can design soaps with specific properties for specific purposes. And yet, in some ways, we're still grappling with the same issues ancient soap makers faced: What ingredients should we use? How do we make this affordable? How do we balance effectiveness with gentleness?
[pause, sound of yawning]
Soap connects us to human history in this tangible way. That bar in your shower? It's made using chemical principles understood by medieval alchemists and ancient Babylonians. The process might be more refined, the scale might be larger, but the fundamental transformation—fat plus alkali equals soap—that's unchanged.
And there's something reassuring about that. About having this connection to the past, to human ingenuity and problem-solving. We figured out that we could take these simple materials and create something useful. And we've kept doing it, kept refining it, kept finding new variations, for thousands of years.

Closing
[Soft ambient music begins to fade in]
So, um, that's the story of soap. From ancient Babylonian clay tablets to modern craft breweries of the soap world, from medieval guild secrets to industrial saponification, from simple hygiene to public health necessity.
It's the story of a chemical reaction—saponification—that humans discovered long before we understood chemistry. It's the story of craft and commerce, of taxation and regulation, of wartime necessity and peacetime luxury. It's global and it's intimate, high-tech and traditional, ubiquitous and yet still somehow mysterious.
[pause]
The next time you wash your hands, maybe think about those soap molecules arranging themselves around tiny droplets of dirt. Think about the fatty acids and the lye, about the medieval guild masters and the modern craft soap makers, about the chemistry that was once alchemy, about the simple miracle of getting clean.
Thank you for listening to Dormant Knowledge. If you're still awake and hearing my voice, I appreciate your attention. But if you've drifted off to sleep somewhere along the way—which was partly the goal—then you won't hear me say this anyway. Either way, I hope some knowledge about soap and saponification has made its way into your consciousness or perhaps your dreams.
Until next time, this is Deb wishing you restful nights and curious days.
[Music swells slightly then fades out]
END OF EPISODE

Show Notes & Resources

Key Historical Figures Mentioned

Michel Eugène Chevreul (1786-1889) French chemist who revolutionized our understanding of fats and oils. In 1823, he published groundbreaking research explaining the chemical nature of saponification, finally revealing how soap actually works at a molecular level. His work laid the foundation for modern soap chemistry.

Nicolas Leblanc (1742-1806) French chemist and physician who developed the Leblanc process for producing soda ash (sodium carbonate) from common salt. This innovation made alkali affordable for the first time, transforming soap from a luxury item to something potentially accessible to everyone. Tragically, he never profited from his revolutionary invention.

Ernest Solvay (1838-1922) Belgian industrial chemist who developed the Solvay process, a more efficient method for producing soda ash that eventually replaced the Leblanc process. His innovation further reduced soap production costs and had lasting environmental benefits.

William Procter and James Gamble Founded Procter & Gamble in 1837 in Cincinnati, originally as a soap and candle company. They revolutionized soap marketing and production, creating Ivory soap in 1879—famously "99 and 44/100% pure" and the floating soap that resulted from a happy accident.

Important Chemical Concepts

Saponification The chemical reaction between fats/oils (triglycerides) and an alkali (like lye) that produces soap and glycerin. This process breaks down fat molecules and reorganizes them into soap molecules that can surround and lift away dirt and oils.

Micelles Spherical structures formed by soap molecules in water, with hydrophobic (water-fearing) tails pointing inward and hydrophilic (water-loving) heads facing outward. These structures trap dirt and oil, allowing them to be rinsed away.

Amphiphilic Molecules Molecules like soap that have both water-loving and water-fearing parts, allowing them to bridge the gap between water and oil—the key to soap's cleaning power.

Lye (Sodium/Potassium Hydroxide) The caustic alkali essential for saponification. Sodium hydroxide produces hard soaps, while potassium hydroxide creates soft or liquid soaps.

Modern Applications and Connections

Public Health Impact The COVID-19 pandemic highlighted soap's continued importance as one of our most effective tools against viruses. Soap molecules literally tear apart viral envelopes, demonstrating how ancient chemistry remains vital to modern health.

Environmental Considerations Today's soap industry grapples with sustainability challenges, from palm oil deforestation to plastic packaging waste. The craft soap movement often emphasizes traditional, environmentally-friendly methods and ingredients.

The Craft Soap Renaissance Modern artisanal soap makers are reviving historical techniques while incorporating contemporary knowledge about skin health, sustainability, and chemistry. This movement connects us to centuries of soap-making tradition while addressing modern concerns.

Industrial Innovation From synthetic detergents to probiotic soaps, the industry continues to evolve. Current research explores waterless alternatives, microbiome-friendly formulations, and biotechnology applications in soap production.

Further Learning

Books:

• Soap: Making It, Enjoying It by Ann Bramson - A well-regarded guide to soap-making history and techniques

Amazon.com

• Caveman Chemistry by Kevin Dunn - Hands-on exploration of historical chemistry, including detailed soap-making chemistry

Amazon.com

• Clean: The New Science of Skin by James Hamblin - Modern perspectives on hygiene, cleanliness, and the role of soap in health

Clean: The New Science of Skin and the Beauty of Doing Less: Hamblin, James: 9780525538325: Amazon.com: Books

Buy Clean: The New Science of Skin and the Beauty of Doing Less on Amazon.com ✓ FREE SHIPPING on qualified orders

Follow

Documentaries:

• "How It's Made" ep 7-06 - Industrial soap production processes explained

Online Resources:

• The American Cleaning Institute scientific archives

Museums:

• The Soap Museum in Sidon, Lebanon - Built on the site of a 17th-century soap factory
• Marseille Soap Museum in France - Dedicated to the famous Savon de Marseille tradition

Episode Tags

#SleepPodcast #EducationalPodcast #SoapHistory #Chemistry #Saponification #MedievalGuilds #IndustrialHistory #ScienceHistory #PublicHealth #ChemistryEducation #HistoryOfScience #CraftSoap #DormantKnowledge #LearnWhileYouSleep #BedtimeStories