Question

Describe the anatomy and the process of leather formation. Which layer(s) of the skin is involved?

Answer 1

Describe the anatomy and the process of leather formation. Which layer(s) of the skin is involved?

Anatomy of leather

The dermis layer of skin is processed to obtain the tanned hide or leather. It consists of bundles of connective fibers which made up of smaller fibrils which are all interwoven to form a three-dimensional "mesh." It is very dense towards the surface or papillary layer and less dense in the reticular layer. There is a mass of protein complex (globulin) between the fibers; the fibrils are composed of a protein called collagen

Structure of the hide           

Starting from the outside, the skin (or hide) has three layers:

• epidermis (1% of the total thickness)
• dermis (85% of the thickness)
• the sub-cutaneous layer or "flesh" (14% of the thickness)

The epidermis and sub-cutaneous tissue is also removed. The dermis is processed to obtain the tanned hide or leather.

Making of leather

The various steps in leather making are:

1. Sammeiring: The water molecules are pressed out of the hide by a process called sammeiring.

2.Splitting: The skins are horizontally split to even thickness. The top layer called Top Grain. It is then ready for trimming, shaving and dyeing.

3.Shaving & Trimming: All the unusable parts of the leather hides are trimmed off and the hides are run through a machine which shaves the back of it to a uniform thickness.

4.Tanning: Tanning is the main process where the skins or raw hides are preserved and converted into leather. It is a chemical treatment. The two main methods are chrome tanning and vegetable tanning.

In Chrome tanning, the hides are treated with basic chromium salts. This process yields a light blue color leather which can accommodate a wide range of colors when dyed.  

Vegetable tanning is carried out by treating the hides with water extracts of various plants or trees. On vegetable tanned leather, the dyed colors will change with exposure to light but a vegetable tanned leather generally possesses an enhanced grain pattern and aesthetic properties .

5.Dyeing: The tanned hides are loaded into large wooden vessels which are filled with water, fats, resins and dyes of various color.

6.Drying:The colored leather are dried in controlled temperature and humidity, and slightly stretched in the process so that they remain supple.

7.Staking :This is a mechanical operation where the hides are put through a machine equipped with a pin wheel which will soften the leather.

8.Dry Milling :At this stage the leather is loaded into dry vessels and milled to the required softness.

9.Buffing :Hides are inserted through a machine equipped with an abrasive cylinder which removes the top surface of the leather.This operation is carried out to remove the various imperfections (scars, tick bites, brands, etc.) before a pigmented finish is applied.Buffing gives a classic velvety look.

10.Finishing: The finishing of the leather is intended to protect the grain surface and give added abrasion , wear resistance ,to render the surface cleanable ,uniformly level the color all over the hide, Cover defects such as scars, tick bites and other imperfections.

11.Pressing & Printing: During this mechanical operation, hides are run through a press, which imprints a texture grain onto the surface of the leather. This is done for aesthetic reasons and to hide defects and imperfections.