Tanning (according to the Chrome method) is a process of treating fresh leather with chemicals to make it durable, supple and to avoid decomposition in the long run. Over 5000 years of development, tanning techniques have also been greatly improved.
- LEATHER PREPARATION PROCESS
Before being put into the tanning process, fresh hides must be cleaned of feathers, blood and remaining fibers under the skin surface. In ancient times, people used a solution of lime or urine to soak and wash their skin.
Today, the pre-processing technique has become much more complicated. This process includes several steps as follows: shaving and grinding to remove hair, lime, and then use other additives to balance the pH. Next, soak the skin in specialized enzymes to soften. Finally, salt the skin or use an acidic solution to lower the pH of the skin.
- SKIN TREATMENT TECHNIQUES
There are three traditional techniques for treating leather: oil tanning, vegetable tanning and mineral tanning.
Oil tanning is the oldest method. Since the Stone Age, people have been applying oil on fresh leather and then smoke it to keep the skin longer. People in Central Asia use a mixture of milk and butter. The Chinese use egg yolks. The Americans used a mixture of animal brain and oil. Vegetable tanning has a development history of nearly 4000 years. With this method, people soak the skin in a solution prepared from plants to create suppleness and firmness for the skin. The ancient Egyptians preferred to use the shame flower, while the Mediterranean region used the sumac tree for tanning. However, the most common is the solution from the bark, oak seeds. Mineral tanning is essentially tanning with alum solution. The leather after soaking in alum has high toughness, and is especially white. White leather was once a luxury item in the Middle Ages in Europe. Today, this is still a method of treating leather before being dyed. In the 19th century, a new tanning method was born: chrome tanning. During primary processing, the leather is treated so that it has a pH, acidity. Next, the skin is soaked with a solution of chrome metal so that the chrome molecules penetrate between the fiber bundles in the skin. This method takes less time than traditional methods and gives the leather a better stretchability, but less elasticity.