The Other Leather
Boiled leather, often referred to by its French translation, Cuir bouilli was a historical material made for various uses common in the Middle Ages and Early Modern Period. It was leather that had been treated so that it became tough and rigid, as well as able to hold molded decoration.
Boiled leather was the usual material for the robust carrying-cases that were made for important documents, pieces of artwork, instruments such as astrolabes, personal sets of cutlery, books, pens and the like. It was also used for armor,
Being both much cheaper and much lighter than plate armor, Leather armor is particularly effective against slashing weapons like curved knives and swords. Most hard leather armor can stop or mitigate a slash from a straight sword.
This type of leather was a historical construction material for armor. It consists of thick leather, boiled in water (some sources hold that oil and wax were used as well) others say the use of ammonia from fermented animal urine. The boiling causes the leather to be harder but also more brittle.
The boiled leather can be fashioned into lames or scales to make lamellar, (Lamellar armor is a type of body armor, made from small rectangular plates (scales or lamellae) leather (rawhide), or bronze laced into horizontal rows or scale armor).
The leather remains flexible for a short time after boiling, allowing it to be molded into larger plates. Boiled leather has also been employed to bind books, Alternative names are "molded and hardened leather". In the course of making the material, it becomes very soft and can be impressed into a mold to give it the desired shape and decoration, which most surviving examples do.
There is one type of leather armor that seems to be quite well documented, and that is Mongolian armor, The Mongols were nomads who had huge herds of animals from which they got most of their food and clothing, and they had access to large amounts of reasonably cheap leather.
This type of armor did not use large leather "plates", but lots of small scales like lamellar that makes repairing the armor very easy. Just undo the lacing or rivets of a damaged plate and replace it with a new one.
Getting high-quality leather for just one or two scales is a lot easier than getting a big piece for a cuirass (a piece of armor consisting of breastplate and backplate fastened together). no one has enough knowledge about how actual leather armor was made, how it worked, and when and where it was actually used historically.
Leather armors were quite popular in ancient East Asia, in places like Mongolia and China. Several thousand years ago there were a lot of elephants, rhinos, and buffalo in central and southern China, and the leather armor that the ancient Chinese used was primarily made from the hide of those large animals.
During the Shang, Zhou, and Warring States periods, most body armors were probably leather armors, while the helmets could be either made from leather or bronze.
However, as the number of large animals declined and technology progressed, the Chinese started to use iron armors. The first iron armors probably appeared sometime during the late Warring States, while mass production of iron armors began in the Han Dynasty.
The ancient Chinese would often apply a lacquer coating to their leather lamellar armors. This would make the leather armors more resistant to rot and harder to penetrate.
Leather armors are not as weak as you think.in a test of a 15th-century European steel crossbow against very rudimentary leather armor. Surprisingly, the steel crossbow did not penetrate the leather armor and the arrow got deflected.
Various recipes for making Cuir bouilli (boiled armor) survive, and none agree with each other; probably there was a range of recipes, partly reflecting different final uses. Vegetable-tanned leather is generally specified.
Scholars have debated the subject at length and attempted to recreate the historical material. Many, but not all, sources agree that actual boiling of the leather was not part of the process, but immersion in water, cold or hot, was.
And that is food for thought