How is leather made?
 |
Introduction
Leather, a versatile material, has been integral to human civilization for millennia. From ancient civilizations to modern fashion runways, leather has remained a symbol of quality and craftsmanship.
Some History of Leather
If ancient paintings and artifacts are anything to go by, animal hides and skins were worn from the Paleolithic period to ancient Egypt, Rome, and many such civilizations that helped in modifying this art form and transforming it into what it is today.
The hides and skins of various animals, such as cowhide, buffalo, sheepskin, goatskin, etc., that may be turned into leather goods like clothing, shoes, purses, accessories, even customized goods, furniture, and more, demonstrate the amazing evolutionary process that the people of today can enjoy the most.
The science behind leather
To begin with, leather comes in several forms and is defined as an animal's hide and skin that, in perfect circumstances, retains all of its natural fiber structure. To prevent it from breaking down, it is tanned, whether it has hair or wool on it.
As previously said, hide is used to cover huge animals like buffalo and cows in situations where horse hide is also utilized. Skins cover a range of smaller animals, such as sheep, goats, and deer, and in some countries, kangaroos, ostriches, snakes, and yes, even alligators.
It's interesting to note that one of the biological components of an animal's skin is the collagen protein, whose chemistry includes a fibrous protein. This point is of great interest to the tanner, as it affects the final appearance of the leather product.
The Working Cycle of How Leather is Made
Beam House Operations
Combined, these phases of the leather-making process, which occur between tanning and curing, are called beam house operations. This section covers deliming, bating, drenching, pickling, soaking, liming, and removal of superfluous tissues (fleshing, hair removal, and scudding).
Soaking
Hides and skins are soaked in clean water to remove the salt that may be left over from curing and to increase the moisture so that the hide or skin can be treated further. Biocides can be used to stop germs of any kind from hiding or damaging the skin while the area is submerged.
Towards the end of the process, fungicides like 2-thiocyanomethylthiobenzothiazole can be used to stop mold growth on wet or damp leathers. Since 1980, it has been forbidden to use pentachlorophenol and mercury-based biocides and their derivatives.
Liming
Following soaking, the hides or skins are taken for liming, a process that involves treating milk and lime and may include the addition of sharpening agents such as cyanides, amines, salt, sulfide, etc. The basic objective of this portion of the process is to remove hair.
The skin or hide's collagen is adjusted to permit proper tanning, a large amount of natural grease and lipids are removed, and certain interfibrillar soluble proteins—like mucins—are employed to expand and split the fibers to the required degree.
Actually, what determines this is the disulfide link breakdown of the amino acid cysteine, which is a feature of the keratin class of proteins that gives strength to hair. the weakening of hair and even wool.
A significant amount of natural grease and lipids are eliminated, the collagen in the hide or skin is corrected to allow for adequate tanning, and specific interfibrillar soluble proteins, including mucins, are used to expand and divide the fibers to the necessary extent.
Actually, what determines this is the disulfide link breakdown of the amino acid cysteine, which is a feature of the keratin class of proteins that gives strength to hair.
The hydrogen atoms in the sharpening agent erode the cysteine chemical bond, which ultimately leads to the dissolution of the covalent disulfide bond links, weakening the keratin.
To a certain extent, sharpening also contributes to hair removal as it tends to break down hair proteins in their entirety.
Scudding and unhairing
.jpg "How is leather made?")
The removal of hair or wool from hides or skins is referred to as unhairing in this context. Agents for dehairing, including calcium hydrosulfide, sodium hydroxide, or sodium sulfide, are utilized.
The remaining hair is removed mechanically, initially through a machine and then by hand using a dull knife. This is specifically referred to as scudding.
Bating and Deliming
This is where the pH (potential of hydrogen) is brought down to the lowest level so that the enzymes may act on it. This is called deliming.
Hides and skins may be treated with enzymes to soften them and make them workable enough, depending on the intended use of the leather. This is referred to as bating.
Modern tanning enables a step to be skipped where bacterial fermentation, achieved through dung-water soaking, is no longer required.
Pickling
If mineral tanning is to be done, the stage following bating and deliming involves treating the hides and skins with sulfuric acid after initially treating them with salt.
Collagen's pH is drastically lowered to do this, which makes it easier for mineral tanning chemicals to enter the material. It is this procedure that is known as picking.
Common salt, sodium chloride, counteracts the negative effects of the abrupt pH drop by penetrating the hides or skins twice as quickly as the acid.
Running the inside of the skin or hide over a steel roller machine will eliminate excess flesh.
How is leather made
.jpg "How is leather made?")
The measurements of the object you intend to construct out of leather are essential, as hides and skins are offered by region. So accuracy is key. Below, we cover the different stages of the process of how leather is made:
Prepping the hides or skins
First off, hides and skins need to be prepped. This involves the removal of the skin or hide from the flesh of the animal. The animal is skinned by placing it in an inclined position on its back.
Using a good hunting knife for skinning is important. The animal is slit from tail to throat after the sex organs are removed, and the skin is then peeled back using a knife or fingers.
After splitting the sternum, the rib cage and other organ removal are carried out. The animal is then flipped over, and the removal of hide or skin is completed.
Most manufacturers use an alternative to this method by using a mechanical fleshing machine to remove the flesh from the inside of the skin or hide. Running the inside of the skin or hide over a steel roller machine will eliminate or lessen the inclusion of excess flesh.
Buying fleshing instruments from a hunting or taxidermy supply store might be a wise choice if a fleshing machine is not available.
Next, the flesh is draped over a large horizontal beam where a small section of the hide or skin is pinned to the end of the beam. The hide or skin can just be laid out on a sheet on the ground if a beam isn't available.
It is important to note that a large basin or bucket placed below your work area to catch any excess tissue or fats as they are scraped away is a good idea. The hide or skin is then rotated until the surface is complete.
Breaks of any kind should be avoided, as they may lead to the material drying out. The final product following fleshing should have a white, smooth surface.
Salt the skin
.jpg "How is leather made?")
The skin or hide is generously covered with salt, which serves as a preservative to prevent the material from deteriorating. Fresh skins or hides need to be salted or frozen within the first few hours, or they may get destroyed.
Next, the material is folded in half so that the flesh sides are together, leaving it for approximately twenty-four hours. Any residue or remaining salt that is found is scraped away, and this step is repeated.
Soaking the hide or skin
This step aids in cleaning the hide or skin of any debris or other items. In a large 35-gallon or so container with fresh, cool water, the skin or hide is placed for at least a day. The longer you let it soak, the easier it may make the hair removal process.
Hair removal from the skin
This can be accomplished chemically with a solution or calcium oxide, aKA slated lime, whitewash, or calcium hydroxide. You can use the same instruments that were used for fleshing in order to dehair. Skin or hide may be hung to dry after hair removal.
A Final Bath
Adding a teaspoon of calcium hydroxide per gallon of water to create lime water, a final bath is given to the hide or skin to remove any inter-fiber substances or unnecessary proteins.
Additionally, it will aid in skin softening and loosening any last hair follicles. To ensure the surface is completely clean, one last rinse is used once the material has been taken out of the lime bath.
Deciding on a Tanning Process
Speaking of tanners, let's examine the leather tanning system, which is connected to the entire leather manufacturing process. First off, hides and skins are sent to a tannery, which is the place where tanning (a process of treating the hides and skins of animals to produce leather) is carried out.
Tanning hide into leather involves, for the most part, a process that permanently alters the protein structure of hide or skin, as mentioned above, making it durable and less, if not totally unlikely, of decomposition. Also, in some cases, give it another color.
Prior to tanning, the hides or skins go through hair removal, are degreased, desalted, and soaked in water for anywhere from six hours to two days.
Glancing through history, we are told that this process of tanning used tannin, which is an acidic chemical compound from which the tanning process draws its name.
Tannin is a German word that refers to the compound's source, which is oak or fir trees. On the arrival of the Industrial Revolution, a type of chromium, which is another solution, was adopted by tanners.
Getting hides or skins is the first step in the tanning process; ideally, no animals are killed specifically for this reason. These hides or skins go through curing to prevent the decomposition of the protein substance called collagen from bacterial growth.
Curing removes the water from the hides or skins, using a difference in osmotic pressure. Bacteria cannot develop when there is an increase in osmotic pressure because it causes a drop in moisture content. In ‘wet-salting’, the hides or skins are salted and then pressed into packs for approximately a month.
But with "brine curing," the hides or skins can be stirred for around sixteen hours in a saltwater bath. Still another mode of curing can be accomplished by preserving the hides or skins at very low temperatures.
Depending on which method you choose, this process can take anywhere from one to four days. After this, the leather is cut based on the user’s requirements. The types of tannins utilized in relation to the process of making leather are as follows:.
Vegetable Tanning
This uses tannin extract, which is found naturally in the bark of many different trees, including hemlock, oak, chestnut, and tanoak. The tannin extract is mixed with water and placed in a rotating drum along with animal skin or hide.
The rotation of the drum will apply the extract evenly throughout the hide or skin. This method yields flexible leather that is frequently used for luggage or furniture, and it takes three to four days.
Mineral Tanning
This process involves the use of a chemical called chromium sulfate, which has to soak sufficiently into the animal hide or skin to achieve proper tanning.
Stretchable leather, perfect for purses and clothing, is the result of this procedure, which takes around twenty-four hours to finish.
Drying the leather
After the hides or skins have gone through the tanning process, they can be considered leather. Hang the leather out to dry over rods in a cool, semi-moist area. While it is possible to use a fan to hasten the drying process, it is recommended to dry leather gradually and carefully.
If the leather isn't drying uniformly, it's a good idea to remoisten the sections that are drying more quickly using some damp towels.
The leather is hung out to dry over rods in a cool, semi-moist place.
Soften the leather
A machine called a staker can soften the leather by stretching it and lubricating it with natural oils. This process ensures the leather stays pliable.
An alternative is to also hang the hide or skin from the ceiling and stretch it as much as possible in different directions. Ropes and hooks may also be used to keep the hide taut.
Softening Oil Application
When the leather is eighty percent dry, an oil application is used on the surface. It is important to even the application out on the surface. The drying process allows for further iterations of this procedure.
Smoke the Hide
