Leather and Hide Processing Notes

Surface Sample

• Fine-pored, may be slightly granular.

• Less patterned, smoother, softer.

• Hairy version: rougher, sparser hair.

• Woolly, denser, warmer fur.

• Color (in raw state): yellowish, grayish. Lighter, whitish.

Leather Examples

• Goat Leather:

  • Example products: Products made from goat leather

• Horse Leather:

  • Properties: Dense fiber structure, extremely durable.

  • Uses: Shoes, belts, premium bags.

  • Example products: Products made from horse leather

Cutting of Raw Hides

• Limitations exist in reducing defects using technology and materials.

• Hides are often cut before manufacturing in their raw state.

• Cutting is based on structural and thickness differences.

• Preparation methods vary depending on size and intended use.

• Different parts of the hide have varying degrees of stretch, justifying cutting.

• Kruponálás (Cutting into Krupon):

  • A common cutting method.

  • Divides the hide into previously identified sections (back, neck, belly).

• Halving:

  • Common cutting method.

  • For cattle hides, halving occurs along the spine.

  • For horse hides, halving occurs perpendicular to the spine.

• Partial Cutting:

  • Involves cutting off only the belly sections.

  • The neck and back (krupon) remain intact.

  • These parts are sold as csuka or félcsuka.

• Kuláta:

  • The back part and belly edge part remain together after the neck part is cut off.

Evaluation of Raw Hide

• Leather manufacturers assess the value of hides based on:

  • The hide's condition.

  • The thickness and size ratios of different parts.

• Good Quality Hide:

  • Large back section.

  • Even thickness.

  • Thickness proportionate to size (thinner hides are smaller, thicker hides are larger).

  • Dense neck and belly edge sections.

  • Most valuable for leather processing.

• Poor Quality Hide:

  • Small back section relative to other parts.

  • Rapid thinning towards the neck and belly edge sections.

  • Thin relative to its size.

  • Many loose structure parts.

• Flat Hide:

  • Evenly thins towards the neck and belly edge but is thin relative to its size.

• Empty Hide:

  • Thin and loose structure throughout.

• Málas Hide:

  • Loose, spongy, and thin structure.

Other Materials in Raw Hide

• Besides proteins, water, and fat, raw hide contains approximately 1% mineral salts.

• Mainly sodium, calcium, magnesium, and iron compounds.

• Most of these are removed during leather production.

• Animal raw hides also contain pigments, enzymes, carbohydrates, volatile substances.

• These make up less than 1% and are removed during tanning.

Topography of Raw Hide

• Topography:

  • From Greek, originally meaning "description of a place."

  • In the context of animal skin, it refers to describing body regions and their relationships based on fiber structure differences.

Division of Skin Area

• The physiological functions of skin vary across different body regions, leading to differences in properties.

• The skin's structure and quality differ because it performs different tasks and experiences varying stress levels on different body parts.

• The back of the animal is most exposed to the elements and therefore the strongest.

• The skin under the abdomen is the most protected, thin, and supple.

Structure of Raw Hide

• Histological Structure:

  • Histology: The study of the tissues that make up living organisms.

  • Tissue: A collection of cells and their formations that are interconnected.

Basic Tissues of the Skin

• Epithelial Tissue:

  • Composed of partially living and partially dead cells.

  • Cells closer to supporting tissues are spherical or cylindrical.

  • Cells become flatter further from supporting tissues.

  • Outermost cells die and detach as scale-like formations.

• Connective Tissue:

  • Located outside cells.

  • Consists of fine, net-like fibrous formations.

  • The fineness decreases with age.

  • The finest strands (fibrils) combine into larger units (fibers) and finally fiber bundles.

  • Fiber bundles intertwine, appearing endless.

  • Tendons and the dermis layer of the skin are made of connective tissue.

• Muscle Tissue:

  • Composed of elements capable of contraction.

  • Striated muscle tissue is found in skeletal muscles and consists of long fibers capable of rapid contraction and elongation.

  • Smooth muscle tissue is found in blood vessels and internal organs, mainly composed of long, spindle-shaped cells.

  • Muscle tissue is found in the skin in the fatty layer, the muscle moving hair follicles, and in sweat glands.

• Nerve Tissue:

  • Composed of nerve cells and nerve cell extensions.

  • Nerve cells consist of thin strands held together by connective tissue.

  • Thicker nerve fibers lead to glands and hair papillae.

Layers of Raw Hide

• The skin of different mammals is histologically very similar due to the identical roles it plays, be it on cattle, sheep, or pigs.

• Identical functions require similarly structured skin.

*Epidermis:
* Comprises 1-2% of the skin's thickness.
* Consists of a cellular structure.
* Removed from raw hide.
* Forms the grain or hair side of finished leather.
*Dermis:
* Comprises 86-88% of the skin's thickness.
* Consists of a fibrous structure.
* The actual leather material.
*Fatty Layer (Hypodermis):
* Comprises 10% of the skin's thickness.
* Consists of coarse fibrous tissue.
* Contains much fatty tissue.
* Removed from the skin.

Definition of Raw Hide

• Raw hides are animal skins used as raw materials in the leather and fur industries.

• With few exceptions, animals are slaughtered for their meat, making raw hide a byproduct of meat production.

• Fur-bearing animals (e.g., fox, hamster, muskrat, polecat) are raised for their valuable pelts when their meat is unsuitable for human consumption, making the raw fur the primary product.

• The value of raw hide accounts for approximately 50-70% of the value of finished leather, making knowledge of raw hide crucial in leather manufacturing.

• This knowledge must cover the structure, topography, preservation, and characteristics of raw hides.

Functions of Skin on a Living Animal

• The skin serves as a separating yet connecting organ between the external environment and the animal's internal systems.

• Its functions are diverse.

• The most obvious role is separation and isolation but the skin is an active, living organ.

• It constantly performs tasks outward and inward, adapting to changing external conditions and internal needs.

• The functions of animal skin can be summarized as follows:

  • Protects the animal and underlying organs from the weather (cold, heat) and external injuries.

  • Provides sensation (cold, heat, pain).

  • Excretes substances through glands (sweat, sebum).

  • Facilitates respiration.

  • Regulates heat balance through evaporation (contraction or expansion).

• Animal skins used by the leather and fur industries in the state between skinning and manufacturing are called raw hides.

• The quality of finished leather depends on the properties of the raw hide, making accurate knowledge of the raw material important for professionals.

• Although properties vary among different types of raw hides, there is some uniformity in the histological structure and chemical composition of mammal skins, especially those most widely used.

• The structure of the skin is studied from two perspectives:

  • Histology: Deals with the structural elements and composition of the skin.

  • Chemical composition: Involves identifying and quantifying the chemical groups that make up the skin using analytical methods.

Factors Determining Raw Hide Quality

• The leather industry primarily uses the skins of vertebrates, especially mammals, though the skin of almost any higher-order animal can be used for leather production.

• Footwear, outerwear, and leather goods are most often created from the skins of large domestic animals.

• In addition to cattle hides, the leather industry uses horse, goat, sheep, and pig skins as important raw materials.

• Deer, roe deer, chamois, and rabbit skins are processed in smaller quantities.

• Various reptile skins and goose and turkey leg skins satisfy specific needs.

• Different methods of leather production can produce finished leathers suitable for different purposes, but proper and targeted selection of raw hides is essential for high-quality and economical production.

• In addition to the histological structure and topography of raw hides from various animals, it is also necessary to understand other factors affecting quality.

Species-Dependent Properties

• The quality of the skin depends largely on the species of the animal.

• Species-specific characteristics such as chemical composition, fiber structure arrangement, density, and skin surface area determine the type of finished product that can be manufactured from the skin.

• Cattle hide is characterized by a thick dermis layer relative to the thin epidermis and fatty layer.

• Within the dermis, the papillary layer is thinner, and the reticular layer makes up the majority of the skin.

• The epidermis is thin, accounting for only 0.5-1% of the skin of a mature animal.

• The dermis is thick, accounting for 80-85% of the skin.

• The papillary layer accounts for only 15-20% of the dermis, with the reticular layer making up the greater portion.

• The fatty layer accounts for 15-20% of the total skin thickness.

• The reticular layer is not only thick, but the fibers are densely interwoven and arranged at high angles, resulting in a firm skin.

• Hair follicles are located throughout the skin.

Raw Hide Processing Steps

• Raw Hide (Fresh or Preserved):

  • Pre-Tanning Operations:

    • Soaking

    • Liming

    • Hair Removal

    • Fleshing

    • Deliming

    • Bating

  • Pelt

  • Tanning (depending on the tanning agent):

    • Vegetable Tanning

    • Mineral Tanning

    • Other Tanning

    • Combination Tanning

  • Tanned Leather

  • Post-Tanning Mechanical Operations:

    • Dehydration

    • Setting Out

    • Drying

    • Softening

    • Shaving

    • Splitting

    • Buffing

  • Unfinished Leather

  • Finishing Operations:

    • Mechanical Operations:

      • Ironing

      • Embossing

      • Pressing

      • Rolling

    • Chemical Operations:

      • Coloring

      • Oiling

      • Grain Enhancement

      • Dyeing

      • Impregnating

  • Finished Leather

Gluing

• Gluing: permanently joining two surfaces with an inserted layer.

• Factors affecting proper gluing strength:

  • A) Adhesive properties of the glue, which depend on:

    • Type of glue.

    • Temperature.

    • Density.

    • Working time (open time).

    • Layer thickness.

  • B) Preparation of the surface to be glued:

    • Cleanliness (free of dust and grease).

    • Roughness.

  • C) Mechanical effects after gluing:

    • Rubbing.

    • Hammering.

    • Pressing.

• The adhesive properties of the glue.

• Adhesives exert their effects through surface adhesion (adhesion) and the attraction between glue molecules (cohesion).

• Cohesion increases when the glue loses its solvent content, and van der Waals forces develop between the polymer molecules.

• Cohesion may increase further in the case of crystallization.

Types of Gluing

• In leather craft, three forms of gluing are used:

  • Edge gluing or thinlayer gluing.

  • Full surface gluing, laminating.

  • Spot gluing.

• Edge gluing is mainly used for hemming, gluing linings and inserts, and the width can vary from a few mm to 1-2 cm.

• Laminating is necessary, for example, if the material (component) is to be glued to cardboard or canvas over the entire surface.

• Spot gluing is generally only used for temporary gluing, e.g. fixing foam to an insert.

• Gluing operations:

  • A) Preparation of the surface to be glued:

    • Cleaning, removing grease and dust.

    • If necessary, roughening, sanding.

Gluing Safety

• Solvent-based adhesives are not only expensive but also harmful and flammable.

• They should be stored in closed containers in a metal cabinet.

• Exhaust equipment or constant ventilation is required for prolonged application.

• In larger plants, laminating larger surfaces usually takes place in a separate room.

• Smoking is prohibited in these areas!

• Leather manufacturing plants are increasingly switching to water-based adhesives or using self-adhesive tape.

• Where possible, gluing operations are eliminated.

• It is now common for individual parts to be assembled directly on the sewing machine without gluing.

Gluing Process

• After applying the glue (usually with a brush or glue roller), allow the glue to dry until it becomes translucent (dries). After observing the specified drying time.

• If necessary, thermoplastic adhesives can be reactivated by heat radiation (heat activation).

  • D) After gluing, mechanical operations must be performed to achieve lasting gluing strength (rubbing, hammering, pressing).

Adhesive Selection

• Various adhesives with different binding agents and solvents have different bonding strengths, so the most suitable adhesive can be selected for each material type and technological operation, taking into account the following aspects:

  • Adhesive bond strength,

  • Type of material to be glued,

  • Technical and intended use,

  • Cost-effectiveness,

  • Health and safety aspects,

  • Working time.

• Most adhesives are organic solvent-based. These are not only

Comparison of Different Adhesives

Pickling in Leather Craft

• In the leather craft profession, pickling of leather (or "pre-tanning pickling") is one of the preparatory steps of leather processing.

• The purpose of pickling is:

  • To improve or unify the color of the leather,

  • To prepare for the tanning process,

  • To adjust the pH of the skin,

  • As well as preservation.

• During pickling, the leather is usually immersed in an acidic medium (e.g. acetic acid solution), often with salt and other excipients.

• This helps the tanning agents (e.g. chrome salt, vegetable tannins) to penetrate the leather fibers more efficiently and evenly.