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Speaker 1: Welcome to brain Stuff from house Stuff Works dot com

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

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Speaker 1: what is leather and where does it come from? Most

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Speaker 1: people in the United States touch a piece of leather

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

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Speaker 1: and car seats. If you ride a Harley or a horse,

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Speaker 1: leather is essential. Leather is all around us and has

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Speaker 1: been for thousands of years. Leather is strong, supple, flexible,

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Speaker 1: and long lasting. But what is leather and how do

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Speaker 1: people make it? It starts with an animal. Most of

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Speaker 1: the leather that we used today comes from cattle. Leather

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Speaker 1: is made from their skin. Since the beef industry in

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Speaker 1: the United States kills millions of cows every year, there's

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Speaker 1: plenty of raw material to work with. The first step

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Speaker 1: in making a piece of leather is to cut the

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Speaker 1: skin off the carcass and clean it up. On the

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Speaker 1: inside of the skin, cleaning means the removal of all flesh, fat,

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Speaker 1: and membranes from the skin. On the outside, cleaning means

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Speaker 1: removing all the hair. To get rid of the hair,

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Speaker 1: the skin is soaked in. A basic solution containing lime

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Speaker 1: that loosens the hair, which is then scraped off, either

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Speaker 1: by hand or with machines. This clean skin is called rawhide.

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Speaker 1: If you have a dog and you buy your dog

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Speaker 1: a rawhide treat, this is what you're buying. As you

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Speaker 1: know if you've ever seen a rawhide treat. Dry rawhide

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Speaker 1: is nothing like leather. Rawhide is hard, stiff, and coarse.

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Speaker 1: If you soak rawhide in water, it regains its flexibility,

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Speaker 1: but as soon as it dries out, it gets hard again.

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Speaker 1: In order to turn this rawhide into leather, something has

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Speaker 1: to change. The change that occurs is a modification of

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Speaker 1: the protein and collagen molecules in the skin. The process

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Speaker 1: that affects the change is called tanning. The word tanning

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Speaker 1: comes from one of the chemicals originally used to cause

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Speaker 1: proteins to change, tannins. If you were to go back

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Speaker 1: in time several centuries to Europe or the American colonies,

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Speaker 1: people made and used a lot of leather. They needed

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Speaker 1: it for shoes, saddles, clothing, armor, books, bags, straps, whips.

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Speaker 1: To make this leather, the animal skins were soaked in

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Speaker 1: a tea made from tree bark. For example, the bark

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Speaker 1: of oak trees. The bark contains the tannins, so they

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Speaker 1: would shred the bark and boil it in water for

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Speaker 1: an hour or so to leach the tannins out of

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Speaker 1: the bark. Then they would soak the animal skins in

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Speaker 1: this tea for many weeks. The tannins in the tea

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Speaker 1: would bind to the proteins and collagen in the skin

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Speaker 1: and change the skin from rawhide and to leather. In

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Speaker 1: a modern leather factory, they use chromium salts instead of tannins,

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Speaker 1: and the chromium speeds the process of tremendously soaking rawhide

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Speaker 1: and chromium salts takes only hours instead of weeks, but

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Speaker 1: the same thing happens. The chromium salts bind the proteins

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Speaker 1: and collagen in the skin and create leather from rawhide.

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Speaker 1: Once tan, the leather can be dyed, dried, and polished

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Speaker 1: and cut up for use. It's also grated. Full grain

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Speaker 1: leather is the highest quality. You are looking at the

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Speaker 1: hair side of the natural animal skin. An he cuts,

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Speaker 1: Scrapes or imperfections in the skin show through. Top grain

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Speaker 1: leather is a lower grade but often looks more uniform.

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Speaker 1: The leather is usually sanded to remove any imperfections and

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Speaker 1: then embossed to recreate the surface like that of full

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Speaker 1: grain leather. Next is split grain Maine firm leather split

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Speaker 1: off for full grained leather. In the process of making

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Speaker 1: the full grained leather and even thickness, it's the inner

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Speaker 1: skin layers that are sanded and embossed. Leather has a

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

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Speaker 1: leather doesn't do particularly well when soaked in water, so

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Speaker 1: in the age of plastics, there's synthetic leather made of

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Speaker 1: flexible vinyl glued to a layer of fabric. Vinyl is

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Speaker 1: the nickname for polyvinyl chloride, one of the most common plastics.

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Speaker 1: PBC is strong and durable, and its water resistant, and

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Speaker 1: it's cheap. About half the weight of a piece of

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Speaker 1: vinyl is chlorine, which is inexpensive because it's easily created

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Speaker 1: from salt. Salt is inexpensive because the ocean is loaded

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Speaker 1: with salt. A gallon of sea water contains about a

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Speaker 1: quarter pounds of salt. The next time you put on

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Speaker 1: a pair of shoes or tighten your belt, think about

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Speaker 1: the leather it contains, whether it's natural leather or sin

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Speaker 1: athetic leather. It's an amazing material. Do you have any

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Speaker 1: ideas or suggestions for this podcast? If so, please send

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Speaker 1: me an email at podcast at how stuff works dot com.

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Speaker 1: For more on this and thousands of other topics, go

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Speaker 1: to how stuff works dot com and be sure to

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