Why is some fur like iron plates, while some fur is very smooth?

Review expert: Zhu Guangsi, science writer

Leather, as one of the earliest materials used in human history, still plays an important role in our daily lives today.

Leather can be used in clothing, shoes, furniture and other fields. Its texture, performance and durability make it a popular choice in the fashion and industrial sectors.

Belt and purse source: pixabay

When we wear a beautiful leather coat or hold a stylish leather bag, we may never think about the long history behind leather, the complex production process and the chemical and physical changes that occur in it. These leather jackets, shoes or bags have undergone a series of fine craftsmanship and numerous changes in the process from the initial animal fur to the final fine and comfortable leather. Today, let us take a look at the development history of leather, the production process and the changes in its properties.

The history of leather

At the dawn of human civilization, people discovered an ancient and magical material during hunting - fur. Previously, plant-derived materials were their only choice for keeping warm during the long winter . However, the untreated fur peeled from the prey was like a hard iron plate after drying, which was far from meeting the needs of our ancestors to keep warm.

But people did not give up. They continued to observe and try to explore ways to transform fur into soft and close-fitting leather. Maybe on a sunny day, someone piled fur on stones to dry, and unexpectedly found that after a period of time, the fur became softer. Or maybe someone buried the fur in soft soil, waited patiently, and finally found that the texture of the fur had changed miraculously .

Leather saddle

Source: pixabay

The attempts of these explorers further aroused people's curiosity, and they began to use different methods and materials to try to make the furs softer and warmer.

For example, exposing fur to different environments and using fire to smoke to make the fur tougher. In the process of continuous trial and error, the ancestors finally discovered a way to make animal fur into leather.

This discovery marked the beginning of leather history and laid an important foundation for the development of leather crafts and leather products in later generations. As a result, leather products entered human life and became one of the indispensable materials for cold-proof appliances, clothing decorations and handicrafts.

Leather production process

Throughout the history of human use of leather, various exquisite leather making techniques have been developed and the production process has also been greatly improved. In the production process, leather is treated with various methods and materials to make it suitable for various applications and needs.

First, the animal's fur needs to be removed, and the animal hair on it must be cleaned. The earliest methods of removing hair include mechanical removal and treatment with alkaline substances. Mechanical removal is to scrape the hair on the surface of the leather with tools, while the use of alkaline substances can strip the connection between the hair and the leather.

After that, it is washed and soaked, first in salt water to prevent bacteria growth and ensure the softness of the leather, and then in clean water to remove salt and impurities, fat, blood, etc. The above steps help to make the leather cleaner and ready for the subsequent process.

Next is the tanning process , which is the most important part of the leather production process. The earliest tanning method should be the use of natural plant materials, such as root bark, bark, etc. Archaeologists have found leather fragments used by ancient Egyptians in the pyramids. After testing, it was found that these leathers were made of vegetable tanning. The tannin compounds contained in these plants react with the collagen in the leather to form a stable complex. This complex makes the leather soft, durable and anti-corrosive.

Tanning process source: pixabay

Before the mid-19th century, most leather used to make shoe uppers was tanned using vegetable tanning, which used plant materials as tanning agents. The ancient Egyptians also used mineral tanning using alum and salt as raw materials. In 1858, on the eve of the Industrial Revolution, a German chemist discovered that chromium salts could be used to tan leather, and the leather produced was softer and more comfortable, lighter and tougher, and easier to dye than vegetable tanning and aluminum tanning (the alum mentioned above). Most importantly, this tanning agent greatly shortened the tanning process and greatly improved the production efficiency of leather. To this day, chrome tanned leather is still widely used in light leathers such as shoe uppers and clothing leather.

After tanning, the leather undergoes processes such as coating, dyeing and polishing, which greatly enhances its appearance and texture. The leather also acquires different colors, textures and glosses, providing a broad space for the production of high-quality leather products.

During the leather-making process, a series of physical and chemical changes occur to transform animal hides into soft, durable leather products.

First, let's look at the physical changes. During the leather production process, the leather goes through multiple soaking and washing steps. During these steps, the hide absorbs water and causes swelling and contraction reactions. This makes the leather fibers softer and more flexible, making them suitable for subsequent processing.

At the same time, the leather also undergoes physical changes such as stretching, scraping and cutting . Through stretching, the fiber structure of the leather is changed, becoming more compact and uniform. The scraping process removes the hair on the surface of the leather, making the leather smoother and easier to handle. Cutting will cut the leather into different shapes and sizes according to specific production requirements.

Chemical changes are crucial in the leather production process, especially tanning. In this process, the collagen in the leather reacts chemically with the chemicals in the tanning agent, cross-linking bonds are generated between the collagen polypeptide chains, and the collagen molecules form insoluble cross-linked complexes. The cross-linking reaction makes the collagen a mesh structure, increases the stability of the collagen structure, and gives the animal fur excellent softness. At the same time, the moisture and heat stability, acid resistance, alkali resistance, and enzyme resistance are also improved.

Chemical changes also include leather dyeing and finishing. During the dyeing process, a chemical reaction occurs between the leather and the dye, and the dye molecules penetrate into the leather fibers, giving the leather rich colors. Finishing is to increase the gloss, wear resistance and water resistance of the leather by applying a transparent protective agent on the leather surface.

After a series of processes, leather is transformed from animal fur with hair into leather that can be used to make clothing, bags, leather boots, etc. Then, after the craftsmen cut, cut and sew on demand, it finally becomes the leather products we see in our daily lives.

In short, leather making is a complex process that requires multiple steps. From the initial animal fur to the final exquisite leather product, each stage is the optimal solution obtained after continuous exploration and innovation.