Understanding, tanning, types and characteristics of leather 1. What is leather? Most consumers habitually associate "leather" and call it indiscriminately. Shoe shopping guide should have a comprehensive understanding of "leather". In fact, "skin" and "skin" are different. They are closely related and have strict differences. "Leather" refers to the skins of various animals (i.e. raw skins), which are transformed into fixed and durable substances through a series of physical and chemical processing and tanning, and are called "leather". Raw hides without physical and chemical tanning are particularly hard after drying, but they will soften and rot easily after soaking in water. After chemical tanning, due to the firm combination and fixation of tanning agent and protein fiber in rawhide, animal skin becomes soft, tough, water-resistant, dry-resistant, damp-heat resistant, chemical-resistant, breathable, water-permeable and anti-aging. Another significant difference between "leather" and "leather" is that most animal skins will start to shrink after being soaked in warm water at 40 degrees Celsius, while leather tanned with chromium salt will not change even if it is put in boiling water at 100 degrees Celsius. Leather has such properties, not only as daily leather products, especially leather shoes, but also widely used in industrial production, becoming a common and indispensable raw material. In addition, it is an indispensable material for military equipment and facilities. For example, military boots, military shoes, aviation clothes and hats, holsters, magazines, Sam Browne belts and saddles are all made of leather. 2. Leather-making technology Leather shoes and various leather products must be chemically treated to make them soft, tough, wear-resistant, breathable, waterproof, heat-resistant and elastic. This process of processing "raw skin" into "ripe skin" (that is, leather) is called "tanning" or "tanning leather". Tanning technology production must go through three processes: preparation, tanning and finishing. A preparation procedures include cleaning, soaking, meat removal, liming, hair removal and liming. After the skins or dry boards are cleaned and soaked, the silt and dirt attached to the skins can be removed and the original soft state can be restored. Then scrape off the oil and carrion attached to the skin, soak in lime water to make the raw rubber fibers on the skin swell properly, and then remove the epidermis and bristles to make the skin white and elastic. The final ash removal is to neutralize the alkaline limewater infiltrated into the skin with acid. Tanning is the main process of making leather from raw hides. Tanning agent and rawhide are put into a regular, symmetrical and slowly rotating wooden barrel, so that the rawhide is constantly turned over, and the tanning agent is promoted to penetrate into the rawhide, which is combined with the protein fiber of the rawhide and fixed to become a water-insoluble substance-leather. The leather made in this way will not stick and rot after drying. Leather tanning methods can be divided into vegetable tanning, chrome tanning, oil tanning and chrome-vegetable tanning. Tanning materials include mineral tanning materials (such as chrome alum and red alum) and vegetable tanning materials (such as tannic acid). Different tanning materials have different uses to make leather. The upper leather for leather shoes is required to be resistant to twists and turns, soft and elastic, and mostly made of mineral tanning materials; Leather shoes bottom leather requires not only resistance to twists and turns, but also strength, firmness and elasticity, so vegetable tanning materials are generally used. C. Leather finishing refers to modification and decoration. Its purpose is to improve product quality; The second is to beautify the goods and make leather products colorful and popular with consumers. Many defects of leather can be made up by careful finishing. Finishing generally includes cleaning, dyeing, elongation, drying, leveling, ironing, oiling, kneading, color spraying, polishing and other processes. Through the continuous processing of these processes, leather can have elasticity, fullness, softness, elongation, water resistance, air permeability, hygroscopicity and other properties. At the same time, the leather surface can achieve fine, smooth and clear grain surface, uniform tone and luster, and beautiful appearance. 3. The types of leather shoes shopping guides must fully understand and master the characteristics of leather, so as to get twice the result with half the effort. There are many kinds of leather. The raw material used in leather making is rawhide (the same below), which mainly comes from ungulates in mammals, mostly from domestic animals, such as pigs, cows, sheep, horses, mules, donkeys, camels and domestic dogs. Followed by wild animals, such as deer, muntjac, wild boar, antelope, antelope and so on. These wild animal skins are excellent raw skins in leather industry, and most of them can be made into high-grade leather shoes (or leather products); Thirdly, seals, hippos, finless porpoises, sharks, whales, snakes, pythons, lizards, crocodiles, ostriches and other animals. Can be made into various high-quality leather shoes or other high-grade leather products with special properties. 4. Characteristics of natural leather There are many kinds of leather, the most common ones are pigskin, cowhide, sheepskin and horseskin. The texture and performance of animal skin are not only different due to the variety, origin, feed and water quality of animals, but also influenced by the sex and age of animals. For example, cowhide is better than buffalo hide, cows in cowhide are thinner than bulls, and the skins of light and strong cows are softer than those of old cows. Jiangsu (Zhou), Wuxi (Wuxi) and Changzhou (Zhou) pigskins have fine pore texture and clear outer dermatoglyphics; Pigskin from Changchun, Shenyang and Dalian has big pores, rough skin lines and deep wrinkles. Inner Mongolia sheepskin is capillary and soft; Sichuan sheep's fur is thick and hard, but its skin is excellent, tough and thick (plate), ranking among the best breeds in the world.