WEBVTT - What is leather and where does it come from?

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<v Speaker 1>Welcome to brain Stuff from house Stuff Works dot com

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<v Speaker 1>where smart happens. Hi Am Marshall Brain with today's question,

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<v Speaker 1>what is leather and where does it come from? Most

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<v Speaker 1>people in the United States touch a piece of leather

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<v Speaker 1>every day. Think about it. We find leather in shoes, purses, belts, jackets, sofas,

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<v Speaker 1>and car seats. If you ride a Harley or a horse,

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<v Speaker 1>leather is essential. Leather is all around us and has

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<v Speaker 1>been for thousands of years. Leather is strong, supple, flexible,

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<v Speaker 1>and long lasting. But what is leather and how do

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<v Speaker 1>people make it? It starts with an animal. Most of

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<v Speaker 1>the leather that we used today comes from cattle. Leather

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<v Speaker 1>is made from their skin. Since the beef industry in

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<v Speaker 1>the United States kills millions of cows every year, there's

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<v Speaker 1>plenty of raw material to work with. The first step

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<v Speaker 1>in making a piece of leather is to cut the

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<v Speaker 1>skin off the carcass and clean it up. On the

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<v Speaker 1>inside of the skin, cleaning means the removal of all flesh, fat,

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<v Speaker 1>and membranes from the skin. On the outside, cleaning means

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<v Speaker 1>removing all the hair. To get rid of the hair,

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<v Speaker 1>the skin is soaked in. A basic solution containing lime

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<v Speaker 1>that loosens the hair, which is then scraped off, either

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<v Speaker 1>by hand or with machines. This clean skin is called rawhide.

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<v Speaker 1>If you have a dog and you buy your dog

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<v Speaker 1>a rawhide treat, this is what you're buying. As you

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<v Speaker 1>know if you've ever seen a rawhide treat. Dry rawhide

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<v Speaker 1>is nothing like leather. Rawhide is hard, stiff, and coarse.

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<v Speaker 1>If you soak rawhide in water, it regains its flexibility,

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<v Speaker 1>but as soon as it dries out, it gets hard again.

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<v Speaker 1>In order to turn this rawhide into leather, something has

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<v Speaker 1>to change. The change that occurs is a modification of

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<v Speaker 1>the protein and collagen molecules in the skin. The process

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<v Speaker 1>that affects the change is called tanning. The word tanning

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<v Speaker 1>comes from one of the chemicals originally used to cause

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<v Speaker 1>proteins to change, tannins. If you were to go back

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<v Speaker 1>in time several centuries to Europe or the American colonies,

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<v Speaker 1>people made and used a lot of leather. They needed

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<v Speaker 1>it for shoes, saddles, clothing, armor, books, bags, straps, whips.

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<v Speaker 1>To make this leather, the animal skins were soaked in

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<v Speaker 1>a tea made from tree bark. For example, the bark

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<v Speaker 1>of oak trees. The bark contains the tannins, so they

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<v Speaker 1>would shred the bark and boil it in water for

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<v Speaker 1>an hour or so to leach the tannins out of

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<v Speaker 1>the bark. Then they would soak the animal skins in

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<v Speaker 1>this tea for many weeks. The tannins in the tea

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<v Speaker 1>would bind to the proteins and collagen in the skin

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<v Speaker 1>and change the skin from rawhide and to leather. In

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<v Speaker 1>a modern leather factory, they use chromium salts instead of tannins,

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<v Speaker 1>and the chromium speeds the process of tremendously soaking rawhide

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<v Speaker 1>and chromium salts takes only hours instead of weeks, but

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<v Speaker 1>the same thing happens. The chromium salts bind the proteins

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<v Speaker 1>and collagen in the skin and create leather from rawhide.

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<v Speaker 1>Once tan, the leather can be dyed, dried, and polished

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<v Speaker 1>and cut up for use. It's also grated. Full grain

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<v Speaker 1>leather is the highest quality. You are looking at the

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<v Speaker 1>hair side of the natural animal skin. An he cuts,

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<v Speaker 1>Scrapes or imperfections in the skin show through. Top grain

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<v Speaker 1>leather is a lower grade but often looks more uniform.

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<v Speaker 1>The leather is usually sanded to remove any imperfections and

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<v Speaker 1>then embossed to recreate the surface like that of full

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<v Speaker 1>grain leather. Next is split grain Maine firm leather split

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<v Speaker 1>off for full grained leather. In the process of making

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<v Speaker 1>the full grained leather and even thickness, it's the inner

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<v Speaker 1>skin layers that are sanded and embossed. Leather has a

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<v Speaker 1>number of useful properties, but it's not perfect. For example,

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<v Speaker 1>leather doesn't do particularly well when soaked in water, so

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<v Speaker 1>in the age of plastics, there's synthetic leather made of

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<v Speaker 1>flexible vinyl glued to a layer of fabric. Vinyl is

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<v Speaker 1>the nickname for polyvinyl chloride, one of the most common plastics.

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<v Speaker 1>PBC is strong and durable, and its water resistant, and

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<v Speaker 1>it's cheap. About half the weight of a piece of

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<v Speaker 1>vinyl is chlorine, which is inexpensive because it's easily created

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<v Speaker 1>from salt. Salt is inexpensive because the ocean is loaded

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<v Speaker 1>with salt. A gallon of sea water contains about a

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<v Speaker 1>quarter pounds of salt. The next time you put on

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<v Speaker 1>a pair of shoes or tighten your belt, think about

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<v Speaker 1>the leather it contains, whether it's natural leather or sin

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<v Speaker 1>athetic leather. It's an amazing material. Do you have any

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<v Speaker 1>ideas or suggestions for this podcast? If so, please send

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<v Speaker 1>me an email at podcast at how stuff works dot com.

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