tanning an animal skin -- 6/16/21
Today's selection -- from How to Invent Everything by Ryan North. If you should get transported back to pre-history, here’s how to tan an animal skin:
"Tanning was originally invented in 7000 BCE. Without tanning, animal skins quickly rot, and even dried ones become hard, inflexible, and brittle. Tanning transforms these skins into leather: a substance so resistant to rot that leather shoes from 3500 BCE have survived into the modern era. It's something you'll definitely want to do, but you should keep in mind that preparing animal skins for tanning involves not only skin fermentation but also soaking them in urine and massaging them in poop slurries, so maybe set up your tanneries downwind.
"Immediately after slaughtering the animals, lay the skins flat and cover the fleshy side in salt or sand, which will dry them out and delay decomposition. In a few days the hides will become hard and almost crispy, and they can then be transported to your tanning area. Once there, you'll soak the hides: this cleans off dirt and gore and softens them up again. Scour the skins to remove any remaining flesh, then soak them in urine -- this loosens the hair, which can then be scraped off. You'll make the poop slurry we advertised earlier by mixing poo and water, and then soak your skins in that: enzymes in the poop will cause the skins to ferment, softening them and making them more flexible. You can help this process by standing in your poop slurry and kneading the skins with your feet -- just keep telling yourself you're crushing grapes -- but be sure to wash up with soap and water afterward, or better yet use nonhuman power (like a waterwheel) to knead the skins for you.
"After all this, two things will have happened: your animal skins will be soft, flexible, and ready for tanning, and nobody will want to get anywhere near you.
"To tan these skins, you'll need to collect some appropriately named 'tannins,' which come from trees containing the equally appropriately named 'tannic acid.' The bark from oak, chestnut, hemlock, and mangrove trees is high in tannin, as is the wood of cedar trees, redwood trees, and more. Tannins are brown, so if you're using wood instead of bark, look for red- or brown-colored wood, and keep in mind that hardwoods generally contain more tannin than softwoods. To extract tannins, shred your wood or bark and boil it in water for several hours. If you've produced it already, adding baking soda to your water will make it more basic, which will draw out the tannins more effectively. You can repeat this process several times with the same bark to produce more dilute tannic solutions.
"After all this, the tanning process is actually the easiest part: just stretch the animal skins out and immerse them in your tannic solutions of gradually increasing concentrations for a few weeks. During this process, the stretched-out skins trade their moisture for tannins, altering the hide's protein structure to make it more flexible, more resistant to rotting, and water resistant. And that's it: you've produced leather! Leather's useful not just for cool jackets; it's also for shoes, boots (you can make both entirely out of leather), harnesses, boats, canteens (leather can hold water without leaking, and it won't break when you drop it like pottery does), whips (fun fact: a whip-crack is actually the sound of a small sonic boom when the tip of the whip exceeds the speed of sound, so technically you're already inventing supersonic technology), and protective armor.
"If you prepare your skin but don't tan it, you'll produce rawhide, which softens when wet but which has the useful property of hardening and contracting when dry. You can exploit that for binding: to attach a blade to a stick and make an ax, just wrap a strip of wet rawhide securely around both and let it dry. Besides making a delicious treat for your dogs (which we can only assume you've already started breeding...), rawhide is useful in making drum skins, lampshades, and primitive horseshoes, and has even been used for casts. If you're doing that, though, be sure to leave some room for it to contract: wrapping limbs in too-tight rawhide has been used for torture. That's right: while rawhide contracting around hands and feet won't produce enough pressure to break bones, it will produce enough pressure to move those bones to places they don't normally go."