Welcome to brain Stuff from house Stuff Works dot com where smart happens. Hi Am Marshall Brain with today's question, what is leather and where does it come from? Most people in the United States touch a piece of leather every day. Think about it. We find leather in shoes, purses, belts, jackets, sofas, and car seats. If you ride a Harley or a horse, leather is essential. Leather is all around us and has been for thousands of years. Leather is strong, supple, flexible,
and long lasting. But what is leather and how do people make it? It starts with an animal. Most of the leather that we used today comes from cattle. Leather is made from their skin. Since the beef industry in the United States kills millions of cows every year, there's plenty of raw material to work with. The first step in making a piece of leather is to cut the skin off the carcass and clean it up. On the inside of the skin, cleaning means the removal of all flesh, fat,
and membranes from the skin. On the outside, cleaning means removing all the hair. To get rid of the hair, the skin is soaked in. A basic solution containing lime that loosens the hair, which is then scraped off, either by hand or with machines. This clean skin is called rawhide. If you have a dog and you buy your dog a rawhide treat, this is what you're buying. As you know if you've ever seen a rawhide treat. Dry rawhide is nothing like leather. Rawhide is hard, stiff, and coarse.
If you soak rawhide in water, it regains its flexibility, but as soon as it dries out, it gets hard again. In order to turn this rawhide into leather, something has to change. The change that occurs is a modification of the protein and collagen molecules in the skin. The process that affects the change is called tanning. The word tanning comes from one of the chemicals originally used to cause
proteins to change, tannins. If you were to go back in time several centuries to Europe or the American colonies, people made and used a lot of leather. They needed it for shoes, saddles, clothing, armor, books, bags, straps, whips. To make this leather, the animal skins were soaked in a tea made from tree bark. For example, the bark of oak trees. The bark contains the tannins, so they would shred the bark and boil it in water for an hour or so to leach the tannins out of
the bark. Then they would soak the animal skins in this tea for many weeks. The tannins in the tea would bind to the proteins and collagen in the skin and change the skin from rawhide and to leather. In a modern leather factory, they use chromium salts instead of tannins, and the chromium speeds the process of tremendously soaking rawhide and chromium salts takes only hours instead of weeks, but
the same thing happens. The chromium salts bind the proteins and collagen in the skin and create leather from rawhide. Once tan, the leather can be dyed, dried, and polished and cut up for use. It's also grated. Full grain leather is the highest quality. You are looking at the hair side of the natural animal skin. An he cuts, Scrapes or imperfections in the skin show through. Top grain leather is a lower grade but often looks more uniform.
The leather is usually sanded to remove any imperfections and then embossed to recreate the surface like that of full grain leather. Next is split grain Maine firm leather split off for full grained leather. In the process of making the full grained leather and even thickness, it's the inner skin layers that are sanded and embossed. Leather has a
number of useful properties, but it's not perfect. For example, leather doesn't do particularly well when soaked in water, so in the age of plastics, there's synthetic leather made of flexible vinyl glued to a layer of fabric. Vinyl is the nickname for polyvinyl chloride, one of the most common plastics. PBC is strong and durable, and its water resistant, and it's cheap. About half the weight of a piece of vinyl is chlorine, which is inexpensive because it's easily created
from salt. Salt is inexpensive because the ocean is loaded with salt. A gallon of sea water contains about a quarter pounds of salt. The next time you put on a pair of shoes or tighten your belt, think about the leather it contains, whether it's natural leather or sin athetic leather. It's an amazing material. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com.
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