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TANNING PROCESS: THE SECRET BEHIND LEATHER'S SHINY APPEARANCE
When it comes to leather, I believe that many people are all familiar with it. In daily life, leather products can be seen everywhere, such as leather shoes, leather clothes, leather bags, leather sofa, leather seat and so on, it can be used almost everywhere. In addition to its practicability, leather products are also often considered as the symbol of high-grade and extraordinary. It is the various production techniques contained behind them which support the popularity of leather products up to now. In this article, you will find out the secret behind leather's shiny appearance.
The most critical process in leather production is tanning. Tanning means the process that raw skin is transformed into cooked skin with moisture, and the cooked skin is cut into multiple layers after subdivision and settlement, and then retanning process which can give the characteristics of fullness, softness and toughness to different finished leather.Different leather products have different requirements for the skin, and the tanning process is also different.At present the main tanning process should be vegetable tanning, chrome tanning, chrome-free tanning, aluminum tanning, oil tanning, let us understand them respectively!
Usually, when we buy leather products, we often see a kind of leather called "Vegetable tanning leather", it is the only environment-friendly leather which will not release toxic substances even if burning. This kind of leather uses one of our human's oldest tanning techniques-vegetable tanning. Vegetable tanning is a relatively environmentally friendly process in which vegetable tanning agents (polyphenolic compounds such as tannins and plant polyphenols) extracted from vegetables are used to process leather. After Vegetable tanning, the leather has good formability, full and elastic surface, no greasy feeling; The grain and suede surface are glossy, it is easy to become soft while contacting with water. The color is various from the natural color of light flesh pink to light brown, it is the best choice for primary color leather products and leather carving.
Chrome tanning refers to the process of tanning leather using chrome powder as a tanning agent. The tanning time and cost are much less than that of vegetable tanning leather. Leather tanned with chromium is bluish-white, so it is called "wet blue". Chrome-tanned leather texture is flexible, fade and shrinkage degree are small, and convenient for dyeing and sewing, mostly used for making clothing or leather bags, etc.
Due to the burning of the leather which is made by chromium tanning will produce the harmful substance "hexavalent chromium", which is harmful to the ecological environment and human health. So under the innovation and development of modern science and technology, chrome-free tanning technology arises at the historic moment. Different from traditional chrome tanning technology, we don’t need to add heavy metal chromium which used in the process of chrome tanning technology in leather tanning, not only can control environmental pollution problem from its source, and also it will be better for the health of people to use this kind of leather products that made by clean technology. Chrome-free tanning technology is not only the demand of the environment, but also the only way for the sustainable development of the leather industry.
Aluminum tanning is a kind of leather tanning which use aluminum salt (aluminum alum, aluminum sulfate and alkali aluminum chloride, etc.) for tanning, and after aluminum tanning, the leather is soft and compact, and it is white, so it is called " wet white leather". The save time for wet white leather is very long, it can be further processed into different types of finished leather, it is a kind of substitute for wet blue leather. Aluminum-tanning leather has a soft surface, close and fine grain surface, but it will de detanning after washing. Wet white leather becomes flat and thin after drying, so aluminum tanning agent will not be used alone.
Oil tanning commonly use seafood animal oil as tanning agent, because it is rich in unsaturated fatty acids, high iodine value and low acid value. The skin which treated with sea animal fat will slowly oxidize under certain temperature and humidity conditions, and its oxidized polymer will wrap the collagen fibers, making the collagen fibers active and hydrophobic. The aldehydes and other oxides produced will cross-link with the skin collagen, and finally tanning will occur. Oil tanned leather commonly known as oil chamois or chamois, selected wild chamois (chamois is a national protected animal now, we often use goat skin, sheep skin, deerskin instead) will be tanned by oil tanning, the leather is light yellow, soft and loose, like woollen, rich in elasticity, extensibility, permeability and water absorption. The traditional oil tanning technology has long tanning cycle, complicated process and serious pollution to the environment, but with the enhancement of people's awareness of environmental protection in recent years, oil tanning technology is constantly improving and developing towards a more environmentally friendly direction.
That’s all for the introduction of the leather tanning technology.
I believe you have become more familiar with the characteristics for all kinds of leather tanning process
You can also try to distinguish what kind of tanning technology it uses when buying leather products.
But the tanning processes mentioned above are only the tip of the iceberg in leather tanning.
As the gears of time move forward, scientific and technological innovation never stops
There will be more and more environmentally friendly tanning process for leather which will be developed
We will continue to share with you more leather trivia
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