Leather Hides:
We mainly use the GOATSKIN, SHEEPSKIN, COW HIDE, BUFFALO HIDE for our leather tanning processing. It is our local animals that are easily available in the market. Also, these leather skins have the best tanning results. We are going to explain the major steps of leather tanning process in our bellow heads that we use after collect the leather hides.
Curing:
Curing is done by treating the hide with salt which prevents putrefaction by preventing bacterial growth on the hide between procurement and processing. It greatly reduces the moisture content of the hide. Another way to cure the skins is by wet-salting, in which the hide is heavily salted and then pressed into packs for up to 30 days. One other way is to soak them in a saltwater brine for about 16 hours.
Soaking:
Salt treated hides are than soaked in water drums and certain chemicals are added to prevent hide from bacterial and fungal growth. Salt treated hides are stiff so It is also done to rehydrate the hides for further processing.
Liming:
Liming is a process used for parchment or leather processing, in which hides are soaked in drums filled with milk of lime, an alkali solution (Calcium hydroxide and sodium sulfide). It’s performed using a drum and paddle or a pit and aid in removal of epidermis, hair roots, fats, proteins and unnecessary elements. The PH of alkali solution is raised to 12 and the hides are soaked up to 24 hours. If preferred for some hides to keep the hair on them, the skin side is treated with a compound that will help to clean and remove hair from that side specifically, leaving the hair-side intact.
Deliming:
The deliming operation in leather processing is a drum/paddle or pit-based operation where two main objectives are met: Removal of alkali from the pelt and the consequent deswelling of the fibers. Firstly, lowering of the liquor pH by using buffering salts to the values used in the bating process. Basically, the hides are washed to remove the final hairs, fleshed, removal of the hair roots and cleaning. It usually takes up to 3 hours to perform this process.
Bating:
Bating involves the addition of enzymes to the hides to soften them. In the process of bating the ultimate goal is to make hides pliable and prepare them for the tanning process. In the bating process, proteases are used to remove scud and unwanted proteins. The process also Deswell’s swollen pelts. The result of bating with the use of enzymes is a clean, smooth and soft hide surface. Basically, it is finally cleaned with clean water. This process consumes up to 4 hours.
Pickling:
Pickling is a step only done for hides that will be chrome tanned. This is because the chromium tanning agents are not soluble under the previously established alkaline environment. Pickling drops the chrome tanning PH to about 2. This process makes the fibers of the hides more receptive to tannin enabling chromium tannings to enter the hide. Salts are added to prevent the fibers from swelling. Basically SALT, SODIUM FORMAT, FORMIC ACID, SULFURIC ACID & BOSAN are used for Anti-Fungus purpose. These chemicals preserve the leather for long time. It is a 24 hours process.
Vegetable tanning:
This is the oldest known common method, and utilizes tannins from plants and bark. In raw hides, the tannins bind to the collagen, covering them. This makes them less susceptible to bacterial growth, less water soluble, and more flexible. The vegetable tanning process can take anywhere from 2 days in the accelerated process, up to 30 days or more in the standard process.
It is usually carried out in large pits, or in large rotating drums and the hides are exposed to stronger and stronger levels of the tannins throughout the process. Since it is a more natural process, the results can be unique and often quite pleasing. The leather produced from vegetable tanning while softer than a raw hide, is still relatively strong and a bit stiff,
Chrome Free leather:
Chrome free tanning is the main type of leather referred to as “chrome-free”, and is often used in automobiles and baby's shoes as it produces very soft leathers. These leathers can be dry cleaned, also washable and are used in automotive industry. Aldehyde tanning is often referred to as “wet white” due to the pale cream color it imparts to the skins. Basically, this leather is produced for the sensitive skin’s people who are allergic to Chrome. This process takes 24 – 48 hours from Pickling.
=> Kindly note this leather is produce only on special demand.
Chrome Tanning:
Chrome tanning is the most popular kind of tanning in the global leather industry. Tanning refers to the process of treating the animal hide to turn it into leather, which is more supple, resilient and suitable for use in various products and due to the properties of chromium, it lends to a soft, thin leather. Though, the overall process can take less than one day. This is usually done in a “one-bath” method at a low PH (2-4). In this method the hides are milled in the single solution until tanning is complete.
Leather tanned with the chromium method can contain about 4%-5% chromium in the material. In the end this is a much faster process than vegetable tanning, requires less labor, and results in a leather that is softer and stretcher.
Piling:
After Chrome process and completion of the process the hides piled up on a table or on the floor to give them a long stay. So, the chrome can properly be absorbed in all skins. Its takes 48 hours to complete this process.
Crusting:
The crusting process involves drying and softening. During the crusting process the tanned hide is thinned, re-tanned and lubricated. There are a variety of processes that may or may not be used at this stage depending on the requirements. During the entire process the pH values of the leather have to be optimally maintained in order to allow it to properly absorb the various chemical agents that are used. Once the pH levels are neutralized, the process of re-tanning is begun and the leather may or may not be dyed at this stage. The leather may also be filled and stuffed to make it harder and heavier and to add oils and waxes between the fibers of the leather. If necessary, the leather may go through a process of whitening in order to lighten the color. During the fixation process, all the chemicals that have been previously used on the leather are either bonded within the leather or removed from it. During the setting process the flatness, grain and area of the leather is determined whilst the excess water is removed. After this the leather is once again dried to reduce the water content to 14-25%. After this the leather is conditioned, softened by separating the fibers and buffed to remove nap or grain defects.
