10.10

“I WANT THINGS THAT WON’T CATCH ON FIRE”

While the inventions in this section have many uses outside of building fireproof buildings, they can help with that problem too. In fact, cement and concrete are building materials that, despite being inexpensive, still allow you to construct buildings that stand for more than a thousand years. Even more useful is steel, an incredibly strong and versatile substance that gives your civilization the ability to construct everything from bridges to ball bearings. Finally, welding allows things larger than can be contained in any kiln to be built and for those constructs to be as strong as if they were made from a single piece of metal.

It is with these technologies that the modern era begins to be restored, so we’re really glad you’re inventing them.

10.10.1: CEMENT AND CONCRETE

The ideal building has three elements: it is sturdy, useful, and beautiful.

—You (also, Marcus Vitruvius Pollio)

WHAT THEY ARE

Building materials you might think of as boring until you realize they can be described as liquid rock

BEFORE THEY WERE INVENTED

Rocks had to be laboriously cut into whatever shapes you wanted, rather than just pouring liquid into a mold, waiting for it to cure, and calling it a day

ORIGINALLY INVENTED

7200 BCE (lime plaster)

5600 BCE (early concrete, used for flooring in Serbia)

600 BCE (hydraulic cement)

1414 CE (rediscovery of cement and concrete)

1793 CE (modern concrete)

PREREQUISITES

kilns (for heating limestone), volcanic ash or pottery (for cement)

HOW TO INVENT

By following the instructions in Appendices C.3 and C.4, you can convert limestone into quicklime, and quicklime into slaked lime—which reacts with carbon dioxide in the air to harden on its own. Add some clay (or sand and water) to your slaked lime, and you’ve just invented mortar: an easily spreadable paste that dries like stone. Replace some of that sand and water with straw or horsehair to increase its tensile strength and you’ve invented plaster: a substance durable enough to be used for exterior coverings that is also waterproof once it’s cured. This makes plaster a great way to build underground food storage: food stays cool, and the plaster keeps any water out.

But all these technologies require air and time to fully cure: plaster can take months! The solution is to add aluminum silicates to your mortar. This creates hydraulic cement: a mortar that not only cures faster and is water resistant but can also cure underwater, which is obviously extremely useful when you want to build lighthouses, breakwaters, and other water-adjacent buildings. Aluminum silicates are found in volcanic ash and clay, so if you’ve got volcanic ash lying around, you can just mix it in with your mortar. If not, take old pottery, crush it up, and add that instead. Horsehair can be added to prevent cracks (just as in plaster), and you can add animal blood too, which will produce tiny bubbles in the cement that make it more resistant to the stresses of freeze-thaw cycles.*

Cement’s great, but you can make it even better simply by mixing gravel, stones, or rubble into it. That’s concrete! This simple addition of literal garbage rocks actually makes the cement much stronger: the rocks carry more of the load, allowing greater and larger structures.* Besides buildings, concrete can also be used to create paved roads. Remember to give your roads a slight slope on each edge (like a roof) and water will drain off, which helps prevent puddles and icing.

Cement and concrete reached an early peak in the Roman Empire, but after that empire fell around 476 CE, the technology was all but lost for a millennium. There were some cement structures built after that date, but the knowledge required was kept within guilds, rarely written down and never disseminated. It was only when an obscure Roman manuscript from 30 BCE (written by the architect and engineer Vitruvius, whose quotation graces this section) was rediscovered in a Swiss library in 1414 CE that the secrets of cement and concrete were recovered.* It took a few hundred years more—until 1793 CE—for that “heat limestone to produce quicklime” discovery to be made, which made cement and concrete simpler to produce. You can easily improve on humanity’s actual history by not forgetting how to make concrete for a thousand years.

You may, for example, choose to store the recipe in a more popular library.

10.10.2: STEEL

The solutions all are simple—after you have arrived at them. But they’re simple only when you know already what they are.

—You (also, Robert M. Pirsig)

WHAT IT IS

An alloy of iron and carbon that’s sturdier than either of those two elements alone, with an incredible tensile strength: the ability to withstand heavy loads without snapping or being pulled apart. Need awesome buildings, tools, vehicles, machines, or anything else? Maybe consider steel.

BEFORE IT WAS INVENTED

Everyone had to “steel” themselves for much more disappointing building materials

ORIGINALLY INVENTED

3000 BCE (iron smelting)

1800 BCE (earliest steel)

800 BCE (blast furnaces)

500 BCE (cast iron)

1000s CE (earliest Bessemer process)

1856 CE (Bessemer process rediscovered by Europeans, which a European then named after a European)

PREREQUISITES

smelters and forges, charcoal or coke

HOW TO INVENT

In Section 10.4.2, we saw how with a smelter you can melt off non-iron metals from ore to extract iron and how you can then hammer that iron in a forge to purify it. But what happens when you add carbon to it? We’ll tell you what happens: carbon interacts with the iron to form an alloy with great tensile strength that also holds an edge. We call it “steel,” and it’s great for making all sorts of things, such as:

Different amounts of carbon give different alloys, and only alloys with carbon levels between 0.2 percent and 2.1 percent get the “steel” label. Even within steels, different carbon levels give different hardnesses and tensile strengths, so you can experiment to find the kinds you like. Kitchen knives—that can hold a tough edge and won’t break easily—have around 0.75 percent carbon.

To introduce carbon to iron to make some sweet, sweet steel, you could pack your iron into boxes of powdered charcoal and heat them to 700°C for about a week. The charcoal’s carbon will react with your heat-softened iron, producing a thin layer of steel. However, only the exterior of your iron will be steel now, so you’ll have to fold and flatten your metal on the anvil again, thereby “stirring” the metal to produce a uniform material. This is obviously a slow and expensive process that requires you to have already hammered and flattened metal to make iron, and then do it again just to get some steel. It may not surprise you to learn that hitting metal with a hammer for hours on end is a long, hot, difficult, labor-intensive, and tedious process that sucks, so you’re going to invent a better way to do it riiiight . . . now.

Hey, congratulations on inventing the blast furnace!

As we’re sure you already know, the blast furnace is basically the intensified version of your forge. Instead of your smelter sucking in air, you now force it in through your materials from the bottom up. And instead of alternating layers of iron ore and charcoal, you’re layering iron ore, limestone, and hotter-burning coke.* You’re producing a more intense combustion that smelts iron ore just like your smelter did, but this goes further: the iron reacts with the carbon in the stack, forming a new alloy with a melting point down near 1200°C: low enough to melt in your furnace! The high-carbon liquid iron runs out the bottom and cools, and you’ve got your metal.

Buuuuuut it’s not quite steel. The problem now is you’ve got too much carbon in your iron: you wanted between 0.2 percent and 2.1 percent, and the output of a blast furnace can be as high as 4.5 percent. This high-carbon iron (also called “pig iron”) is brittle: too easily broken if bent or stretched to be useful in bridges or buildings, but its low melting point does mean you can pour it into molds to cast frying pans, pipes, and so on. This “cast” “pig” “iron” is called “cast iron,” and you just invented it.

To reduce the carbon level of pig iron enough to make steel, you’ll be using the “Bessemer process,” whose basics were discovered in East Asia in the 1000s CE. The idea then was to blow cold air across the molten metal, and the more modern version (patented in 1856 CE by, you guessed it, some guy named Bessemer) is to force air through the liquid pig iron instead, with bellows or air pumps. The air introduces oxygen to the mixture, and the oxygen reacts with the molten carbon to form carbon dioxide. This either burns off or bubbles out, leaving a purer iron behind. And as a bonus, these reactions also generate heat, which heats up the molten metal even more, allowing the reaction to continue even as the melting point of your liquid metal rises.* It’s very hard to know when precisely to stop the bubbling air to get just the right amount of carbon remaining, so don’t bother: just burn off all the carbon you can—producing a pure iron—and then mix whatever carbon you want back in.

Iron is the sixth most abundant element in the universe and the fourth most common element in the Earth’s crust, but until humans invented blast furnaces and the Bessemer process, it was impossible to turn it into steel cheaply or efficiently. But you’ve just figured that out, and now one of Earth’s strongest metals is also one of its cheapest. Nicely done! Once your civilization has engineers in it, they’ll definitely thank you for that one.

A final note on steel: you can produce high-quality steel wire by taking advantage of steel’s high tensile strength and using a technique called “wire drawing.” All you do is make a rough wire out of steel, and then pull it through a cone-shaped hole, as so:

Figure 33: An apparatus to draw wire, as seen from the side.

This produces a wire of consistent area and volume, and that unused mass goes into lengthening your wire. By using several progressively smaller holes, you can produce wires much thinner than you can make by hand. A ratchet (see Appendix H) can be used to pull the steel forward, and conveniently, this can all be done at room temperature: you just need some lubricant.

Here’s where it gets embarrassing for us. In the early 1600s CE grease or oil was used, but this required softer steels, and too much friction would cause the wires to break. By 1650 CE, one Johann Gerdes “accidentally” discovered that if the steel was soaked in urine for long enough, a soft coating would eventually develop (we now call this process “corrosion”), which worked to reduce friction when drawing wire. This process—named “sull-coating”—was used for 150 years until someone noticed that diluted beer actually worked perfectly fine as a substitute, and it was only around 1850 CE that anyone thought to check if water works too. It does. It works perfectly.

Do better than we did. Don’t soak your steel in pee for over a hundred years for no reason.

10.10.3: WELDING

When I told my father I was going to be an actor, he said, “Fine, but study welding just in case.”

—You (also, Robin Williams)

WHAT IT IS

A way to fuse two metals together in a way that can actually be stronger than the base metals

BEFORE IT WAS INVENTED

Any metal item had to be forged as a single piece, because once it existed, the only way to join it to another one was with bolts and screws, which are much weaker than a good weld

ORIGINALLY INVENTED

4000 BCE (forge welding)

1881 CE (arc welding)

1903 CE (torch welding)

PREREQUISITES

metal, forges, electricity (for arc welding), acetylene (for torch welding)

HOW TO INVENT

Forge welding is easy: just heat the two metals you want to weld to about 50 to 90 percent of their melting point in your forge, at which they’re flexible but still solid. The challenge is when metals reach this point, their surfaces tend to oxidize, which prevents a good weld. By sprinkling sand (or ammonium chloride, or saltpeter, or a mixture of all three; see Appendix C) on top of your metal, you solve this problem: they lower the melting point of the oxides, allowing them to flow out from between the two metals as you beat them together. “Beat them together,” you say? Yes. This is not a fancy form of welding, hotshot. This is the form of welding where you heat two metals up and hammer them together until they stick. If your arms get tired, you can use a waterwheel (Section 10.5.1) to produce a mechanical hammer that will strike your metals repeatedly.

If you have electricity (Section 10.6.1), you can invent electric arc welding: a less labor-intensive version that also lets you weld items too big to fit in a forge. Arc welding uses the heat generated by electricity arcing from an electrified piece of metal called an “electrode” to the metals you wish to weld. The electrode is placed near the point on the metals you wish to weld, and the arc jumping from it causes them to melt and fuse together. A rod of a filler metal can also be used to join your two metals together, which can make the weld stronger than the base metals themselves. Just ground your metals,* bring an electrode close enough to arc, and weld away. Try to keep the distance your arc needs to jump consistent: otherwise the current it carries will fluctuate, which alters the heat and therefore quality of your weld.

Needless to say, this option can be insanely dangerous, especially if you’re stranded in the past and have never worked with electricity before.* You’ll probably want to stick with “heating up metals, dumping some sand on them, and hammering them until they stick” for the time being.