What is the weight of a pair of working cattle skins? Classification of the main types of leather and fur raw materials. Soaking and fleshing of cattle skins

Soaking

To obtain soft, high-quality leather, cowhide is soaked in 2 stages:

1. First, the raw materials are immersed in clean water for 4 hours.
2. And after that, for 12 hours it is kept in a saline solution, which is prepared at the rate of 20 g of salt per 1 liter of water. Please note that over time the skin will begin to swell, so experienced experts advise preparing 8 liters of liquid for each kilogram of it.

Soaking is considered to be of high quality when after it the subcutaneous layer is easily removed from the wet-salted workpiece. If difficulties arise, the raw materials require additional aging in a saline solution.
To prevent bacterial infection of skins, tanners advise using a solution based on salt and furatsilin However, you should not leave it in this form for a long time, because the material may deteriorate. Experienced tanners recommend adding 6 furatsilin tablets to each 10-liter bucket of water to prevent bacterial infection of the skins.

Important! The harvested raw materials must be without cuts, since even small punctures reduce its quality.

Mechanical degreasing, fleshing of hides

At this stage of dressing, it is important to carefully remove the subcutaneous fat deposits of the slaughtered animal. Some craftsmen do the fleshing manually, while others prefer to use a special mechanical device, the design of which resembles a rotating disk with sharp edges.

However, without some experience it is dangerous to operate such a device, since incorrectly cut hair follicles will affect the quality of the skin. To get a good result, experts advise removing the fat layer evenly, starting from the tail, with smooth movements from the axial center to the periphery.

Washing

After degreasing, the cowhide must be washed in warm water. To do this, it is recommended to use a soap solution. It is prepared in a ratio of 10 g:1 l. It is best to use laundry soap; soda ash is an alternative.

Did you know? In the 17th–19th centuries, binding made of human skin was used to decorate some books. Most often, treatises on anatomy were decorated in this way. Copies of criminal cases of executed criminals could be bound with leather. And sometimes such books were made from the skin of the deceased according to their will.

Pickling (or pickling)

In order for the prepared skins to change their structure, they are kept in a special vinegar-chlorine solution. For this purpose, acetic acid must be dissolved in water at a concentration of 0.15% and liquid sodium chlorine at a concentration of 0.04%.

Pickling involves periodically stirring the resulting composition after dipping the raw materials into it. Its exposure should last for 12 hours, until white stripes remain on the folds of the material when squeezed.
At this stage of home leather dressing, pickling can be replaced by fermentation. Its technology consists of soaking washed raw materials in an aqueous suspension of oatmeal or barley flour. The solution is prepared from warm water, adding 60 g of salt and 100 g of flour for each liter.

After mixing all the ingredients, you can dip the skin into the resulting mixture, but do not leave it unattended for a long period. Experienced craftsmen advise constantly monitoring the fermentation results, since over-cured material is unsuitable for further processing.

Did you know? The reflex that leads to the appearance of goose bumps is inherited from animals. . The muscles of the hair follicles contract and lift the hairs, causing the animal's fur to stand on end. When reacting to cold, this helps to retain body heat longer; when reacting to danger, it makes the animal more massive and terrifying. In humans, during the process of evolution, there is little hair left on the body, and this reflex has no practical meaning.

Tanning

After these manipulations, the cow hide must be tanned. The technology of this process involves soaking the raw materials for six hours in a special solution of chromium oxide. When preparing it, maintain the proportion of 1.5 g of active substance for every liter of warm liquid. After placing the skin into the resulting mixture, it is important to stir it periodically.
Some livestock farmers carry out the tanning procedure using:

• oak bark;
• stems of stinging nettle;
• willow branches;
• alder biomass.

All components need to be finely chopped and measured in equal parts of 250 g. After that, prepare a saline solution in a ratio of 1: 60 and add the plant mixture to it. The liquid must be boiled and simmered over low heat for half an hour. Then the finished broth is filtered, allowed to cool slightly and the cow skin is soaked in it for 6 hours.

Zhirovka

At this stage, the technology for home tanning of cattle leather involves the preparation of a special emulsion.

It is done by adding the following components to water heated to 45–50 °C:

• laundry soap shavings - 200 g;
• ammonia - 10 g;
• any fat - 80 g.

Mix everything thoroughly, and then carefully treat the inner side of the skin with the resulting product. This is done using a soft brush or swab. After fattening, the hide blanks are stacked and left for 24 hours.

Drying skins

At the final stage, the oiled skins are stretched onto a wooden grid or flooring so that the flesh is located on top. You should not overdo it in this matter, because after so many treatments the skin may tear, but the tension should be noticeable.
During the entire drying period, it is recommended to take the workpiece outside every day to a shady place for ventilation. When the skins in the center zone on the inner side become elastic and dry to the touch, they can be removed. After that, it is recommended to spread the skin on a flat surface and clean the inside with a metal brush.

Did you know? The polar bear has black skin under its fur. The bristles of the fur coat themselves are transparent and hollow, so in different conditions the color of the bear can vary from white to yellowish. In hot countries in captivity, a polar bear may even turn green if algae begins to grow in the bristles.

This will make the material lighter and softer. In this case, sharp jerky jerks are unacceptable. The tool should move smoothly and evenly, which will give the inside of the skin a “suede” velvety feel. Then, until it is finally ready, it is sent to dry for another 2 days.

Video: skin processing

Classifications of cattle skins

Experienced livestock breeders who have mastered the technology of home-dressing cattle skins distinguish several types. Each of them differs in the level of strength and nuances in processing. Let's take a closer look.

Important! If the technology for tanning leather at home involves the use of any acids, remember that ordinary soda will help neutralize their effect. Please note that during the chemical reaction there will be a lot of foam, so choose rooms with good ventilation for work.

This is calfskin, the characteristic feature of which is faded and felted primary wool. The raw materials for the product are animals from birth until the end of milk feeding.

The classification of skins used for tanning for the production of leather products is carried out according to the species of animals and age range. Different hides have different properties and are used to produce different types of products.

Cattle hides

Depending on the type and size, the skins are used to make types of leather used in the production of gloves, haberdashery, shoes and outerwear.

Slimy.

Skin from a stillborn or intrauterine calf. A distinctive feature is the purple flesh. Dimensions up to 700 cm2. It is used mainly for the production of huskies.

Opoek.

Leather obtained from calves from birth until the end of milk feeding. A characteristic feature is faded and matted primary wool. Dimensions up to 800 cm2. Serves as an ideal raw material for the production of husky and chrome leather.

Outgrowth.

Skins of calves that began to eat plant food. It is distinguished by dull hair that has undergone molting and a well-defined spinal stripe. From this variety, the size of the skin begins to be determined by its weight. The mass of the shoot should not exceed 10 kg. Used for the production of husky and fine chrome leather.

Half-skinned.

Skins of grown heifers and bulls, weighing from 10 to 13 kg. It differs from the outgrowth only in mass. In bulls, the skins on the neck have a characteristic thickening (wrinkling), indicating a sexual characteristic. Used to make chrome leather.

Yalovka.

The skin of heifers that have reached puberty and cows. Divided by weight into three groups: light (13-17kg), medium (17-25kg) and heavy (over 25kg).

Goby.

Goby skins weighing from 13 to 17 kg. They differ from cowhide by a smaller area (by about 20%) and pronounced wartiness, reaching half the size of the skin.

Bychina.

Skins of castrated bulls weighing over 17 kg. They are divided into two weight categories: light (17-25kg) and heavy (over 25kg). They differ from the skins of uncastrated bulls in the smaller number of folds on the collar part.

Bull.

Skins of uncastrated bulls, weighing over 17 kg. It is distinguished by its great thickness and intense brushiness.

Half-leather, cowhide, goby, bychina and bull are used for the production of such types of leather as nappa, morocco (rarely), velor, saddle cloth, napplak, shora, yuft, split leather.

Horse skins

Horse skins have a unique structure that makes them very different from the skins of other animal species. The front part of the skin (horse front) is quite thin and less dense than the back part (horse haz). This makes it necessary to divide the hide into two parts and use them for various leather products.

Slimy.

The skin of a stillborn foal or embryo. It is accepted by area, which ranges from 300 to 700 cm2.

Foal.

Skins of foals weighing up to 5 kg. It differs from the slime by its larger area and already pronounced mane.

Marking.

Skins of foals weighing from 5 to 10 kg.

Horsemeat.

A skin weighing more than 10 kg. There are light (10-17kg) and heavy (over 17kg) horse meat.

Horse skins are used to make several types of leather for various needs. From haberdashery production to outerwear tailoring.

Sheep skins

Sheep skins are used as raw materials for leather only when their qualities are not suitable for the fur industry or fur coat production. They are used for the production of such types of leather as husky, chevro, chevrette, morocco (rarely), parchment.

Goat skins

For leather tanning, only the skins of dairy goats are used. The remaining breeds supply fluff and raw materials for the production of fur products. Goat skins are dense, strong, with good uniformity in thickness. This makes them one of the best materials for tanning leather used for making shoes and outer leather clothing. From this raw material such types of leather as Laika, Chevro, Chevret, Saffiano (the best material) are produced.

Pig skins

While pigskins are the cheapest leather raw material, they have long been a staple leather raw material and are used not only to produce a full range of standard leathers, but also to imitate more expensive, improved leathers produced from the skins of other animals.

They are accepted by area, divided into three groups: small (300-700cm2), medium (700-1200cm2) and large (over 1200cm2).

Upon acceptance, any type of leather raw material is classified according to defects, divided into groups and subjected to appropriate types of processing.

Types of leather raw materials

The skins of cattle, pigs, horses, sheep, goats, as well as camels, donkeys, mules, buffaloes, yaks and deer are mainly used to make leather. The skins of reptiles (crocodiles, lizards) and fish are processed in small quantities.

Cattle hides. Cattle hides are the main type of leather raw material. Skins are divided into age categories as follows.

Opoek - slimy - skins of unborn or stillborn calves, weighing in pairs 1.2 - 2.5 kg.

Opoek - skins of calves fed on mother's milk, weighing 1.8 - 3 kg. The skins are covered with primary unshedded wool, which has high softness and shine.

Outgrowth - skins of calves up to seven months old, weighing up to 10 kg, switched to plant feed. The skins have a secondary coat after molting. The area of ​​the skins is 60 - 150 dm², thickness 3 - 4 mm.

Half-skin - skins of heifers and bulls under the age of one year weighing 10 - 13 kg.

Goby - skins of young bulls up to 2.5 years old weighing 13 - 17 kg.

Yalovka - cow skins. Depending on the weight, the skins are divided into light (13 - 17 kg), medium (17 - 25 kg) and heavy (25 - 30 kg).

Bychina - skins of oxen (castrated bulls). Depending on the weight, the skins are divided into light (17 - 25 kg) and heavy (more than 25 kg).

Bull - skins of stud bulls, divided by weight into light (17 - 25 kg) and heavy (more than 25 kg).

Horse skins

Slimy foal - skins of unborn or stillborn foals weighing 1 - 2 kg.

Foal - skins of foals weighing up to 5 kg.

Marking - skins of young horses weighing 5 - 10 kg.

horsemeat - skins of adult horses. There are light (10 - 17 kg) and heavy (more than 17 kg) horse meat.

Usually horse meat is divided into the front part - front and the back - haz.

Pig skins

Pig skins have a mass of up to 1.5 kg.

Pig skins divided into small (30 - 70 dm²), medium (70 - 120 dm²) and large (more than 120 dm²).

Goat and sheep skins

Goat skins have an area from 8 to 120 dm², weight from 0.2 to 5 kg.

Sheep skins (sheepskin) divided into fur, fur and leather. Leather sheepskin includes skins that, due to the condition of the wool, are unsuitable for making fur and fur coats.

The area of ​​leather sheepskin ranges from 30 to 150 dm², weight - 1 - 3.5 kg, thickness - 1 - 3 mm.

In our country, livestock farming is meat and dairy oriented. In this regard, the main type of leather raw material (more than 70% of the total supply) is medium and heavy (Table 1).

As can be seen from the data in table. 1, over the past years, the proportion of calf skins has sharply decreased, the number of light skins has also decreased and the number of medium and heavy skins has increased.

Skin structure

The skin protects a living organism from external influences, serves as an organ of touch, and a regulator of body temperature. Sweat is released through the skin, which is a waste product of the body.

Skin consists of three layers (Fig. 10): epidermis 3, dermis 2 and subcutaneous tissue 1. The thickness of each layer of different types of raw materials varies widely.

Epidermis - a thin (up to 2% of the thickness of the skin of cattle and up to 5% of pigs) surface layer consisting of keratin protein cells. Skins with thick, well-developed hair have a thinner epidermis than skins with little hair.

Dermis consists predominantly of collagen, as well as elastin and reticulin fibers 7, the spaces between which are filled with interfiber substance.

The dermis is divided into upper (papillary) and lower (reticular) layers. There is no sharp boundary between these layers, so the boundary is conventionally considered to be the surface passing through the base of the hair roots. Hair 4 passes through the epidermis and the papillary layer of the dermis, ending in a hair follicle b. In pig skins, the hair penetrates right through the dermis.

The papillary layer also contains sebaceous and sweat glands 5, blood and lymphatic vessels. This structure of the papillary layer makes it relatively loose and fragile.

After removing the hair and epidermis, elevations remain on the front surface of the leg, as well as on the dressed skin, which, together with the indentations of the hair follicles, form a mere - a pattern characteristic of each type of animal.

The reticular layer is very dense and durable, as it does not contain the glands and vessels present in the papillary layer. The ratio of the thicknesses of the papillary and reticular layers depends on the type and age of the animal.

Subcutaneous tissue (sometimes also called mesdra) is located under the dermis and consists of fibers, between which there are fatty deposits 8.

During the production of leather, the epidermis with hair and subcutaneous tissue are removed. In recent years, in the manufacture of some types of leather, the hair has been preserved.

Structure and
The properties of the skin areas are not the same. In the skins and skins of cattle, the following topographic areas are distinguished (Fig. 11, a): saddle cloth 1, collar 2, floors 5, flank 4, bangs 3, paws 6, rump 7. A saddle cloth without a rump is called a rump. The area of ​​the saddle is up to 55% of the total area of ​​the skin.

In horse skins (Fig. 11, b) there is a front part 8, which combines the central, front part, collar, floors, front legs and flanks, and haz 9, which includes the back part of the skin with the hind legs and flanks.

In the skins of pigs (Fig. 11, c) there are 10 croupons, 5 floors and 6 paws.

Chemical composition of the skin

The skin consists of proteins, fats, minerals, and water.

Squirrels make up 70 - 80% of the dry matter of the skin.

Collagen is the most important protein in the connective tissue of the skin. The dermis of animal skins consists of more than 90% collagen.

Collagen is insoluble in water, dilute solutions of acids, alkalis and salts, but under their influence it absorbs large amounts of water and swells. When heated in water at a certain temperature, collagen is deformed (welded), and then turns into protein - gelatin.

Elastin is found in hides in very small quantities. It has high elasticity and is resistant to water: when boiled in it, it does not change its properties.

Keratin is part of the epidermis and hair. Keratin swells in water, and when exposed to concentrated solutions of alkalis, as well as reducing agents (for example, sodium sulfide), it dissolves.

The amount of fats and fat-like products in the skin depends on the type, age, sex and fatness of the animal. Fats and fat-like substances are found in different layers of the skin: on the surface and between the cells of the epidermis, in the layers of the dermis, sebaceous glands and subcutaneous tissue. The content of fats and fat-like substances in the skin of different animals ranges from 2 to 40% of the dry matter weight. Pork and sheep skins are especially rich in fatty substances, which significantly affects the properties of the skin.

Minerals make up less than 0.5% of the weight of a fresh skin. They are represented by sodium chloride, calcium, magnesium, aluminum and iron salts.

The water content of steamed skins is usually 60 - 75%. It varies depending on the species, age and sex of the animals. The skins of adult animals contain less water than the skins of young animals. In a steamed hide, a distinction is made between wetting moisture, which fills the interfiber space and capillaries, and hydration moisture, chemically associated with the active functional groups of the skin proteins.

The skin also contains enzymes, vitamins, carbohydrates and other substances.

Preservation of hides

There are many microorganisms on the surface of the skin, which, after it is removed from the animal, end up on the flesh side and actively multiply there. Microorganisms accelerate the process of decay of animal tissues - rotting. Rotting is expressed in a change in the properties of the skin: a decrease in its strength, an increase in rigidity, a deterioration in appearance, the appearance of a putrid odor and defects in the outer layer.

Already 4 - 5 hours after removing the skins, their processing is difficult due to rotting. A certain number of skins are processed immediately after slaughter, i.e. in a paired state, which ensures high quality skins. However, the bulk of hides can only be processed after a certain period of time, so they must be protected from rotting by preservation. Before canning, the skins are skinned (removal of remaining meat and fat) and washed.

For short-term preservation, the skins are treated with an aqueous solution of chloramine and sodium carbonate, which prevents it from rotting for 7 days. For long-term storage, skins are most often preserved using drying, dry- or wet-salting methods.

Drying is carried out in chamber dryers with skins stretched on frames. Under the influence of high temperatures, microorganisms die and rot does not develop. However, very high temperatures can change the structure and properties of the protein substances of the skin. Drying is carried out until the skin moisture content is 16 - 18%.

When canning using the dry-salting method, sodium chloride is poured onto the fleshy side of the skins. The moisture in the skin dissolves the salt, and the solution is absorbed (diffuses) into its thickness. The hides are salted in piles for 24 hours and then dried in dryers.

The bulk of the skins are preserved by wet-salting, pickling and brining methods. In the first method, sodium chloride with antiseptics is poured onto the fleshy side of the skins.

The hides are salted in piles for 4 to 7 days.

Brining consists of treating hides with a saturated solution of sodium chloride (brine). The duration of brining is 6 - 8 hours for small raw materials and 18 - 20 hours for large raw materials. After brining, the hides are kept in piles for two days, i.e. the entire process of preserving the hides does not exceed three days. The moisture content in wet-salted skins is 46 - 48%. In Fig. Figure 12 shows a diagram of the production line for preserving hides by brine.

When canning by drying, moisture evaporates unevenly, which causes overdrying of the outer layers and retention of excess moisture in the middle layers of the skin. Such skins can rot from the inside, have folds and large shrinkage, and are more difficult to process in subsequent production processes.

With the dry-salted method of canning with sodium chloride, a very common skin defect is salt stains due to the content of sparingly soluble calcium and iron compounds in sodium chloride. To reduce the number of salt stains, sodium carbonate or sodium phosphates are added to the preservative mixture.

Preservation methods by freezing, radioactive and ultraviolet radiation are also known, but they have not found widespread use.

If the technology is followed, leather made from wet-salted preserved hides is practically no different in all property indicators from leather made from paired hides.

For the production of leather, the skins of a wide variety of animals and even fish and birds are used. The main types of leather raw materials are the skins of cattle - cows and bulls; horse, goat, sheep, pork. Less commonly used are the skins of wild boar, deer, dogs, saigas, roe deer, yaks, buffalo, camels, sea animals and fish.

When classifying raw materials, many characteristics are taken into account, among which the main ones are: the type of skin depending on the type of animal, the mass of the skin in kilograms, the area of ​​the skin in square decimeters, the method of preservation.

Requirements for raw hides are regulated by GOST 28425-90 “Raw raw hides. Technical conditions", GOST 28509-90 "Undressed sheepskins. Technical conditions".

The so-called large raw materials are classified by weight: cattle, horse, camel skins. Cattle raw materials are the most diverse and have a classification of types depending on the age of the animal: cow, outgrowth, half-skinned, bull, bull, cow, bull. As the animal ages, the mass, area and thickness of the skins increase.

Depending on the type of animal, the mass in a paired state or the area of ​​the hide, raw hides according to GOST 28425-90 are divided into small, large and pork.

Small raw hides include:

calf skins: slime, calf skin, outgrowth;

camel skins: skins of young camels weighing up to 10 kg;

skins of foals: slick, foal and marking;

goat skins: steppe goat, grain goat, wild goat skins - skins of goats from the family of wild and hornless mammals: wild goat, roe deer, wild gazelle, saiga, argali (wild sheep) and musk deer.

Large leather raw materials include:

half-leather, goby, cow, light, medium and heavy;

bull, light and heavy, bull;

buffalo, yak, elk;

horse front;

horse haz;

skins of camels, skins of donkeys and mules.

Pork hides include:

pork skins - the skins of domestic pigs and hogs.

Depending on the area in the paired state, pig skins are divided into:

for small ones - from 30 to 70 dm2;

for medium ones - over 70--120 dm2;

for large ones - over 120 dm2;

In accordance with GOST 28509-90, rare-wool skins of Russian and steppe fur sheepskin (less than 1000 fibers per 1 cm2), with wool flow in an area of ​​more than 50%, with deep burrs throughout the entire area of ​​the sheepskin, lying at a distance of 1. 5 cm or less from the base of the hair or with heavily felted hair; skins of adult Romanov sheep with an area of ​​less than 35 dm2 and white sheep with an area of ​​less than 24 dm2 with wool flow on an area of ​​more than 50%, with heavily felted wool, with deep burrs on an area of ​​more than 25% of the sheepskin area, lying on more than half the length of the wool and cannot be removed .

For the production of leather in small quantities, the skins of deer, beluga, sea lion, northern seal, Far Eastern seal, as well as whale hides are used.

Cattle hides have a dense structure. The epidermis is thin, the papillary (thermostatic) layer in the skins of young animals is 45-50%, in adults - 30-35% of the thickness. The thickness of this layer varies over the area of ​​the skin and on the back reaches 30-35%; on floors - 50% of the thickness of the dermis.

Cattle hides are divided into groups of small and large raw materials.

Small raw cattle weighs up to 10 kg. These include the following types:

Slimes are the skins of unborn or stillborn calves that are not suitable for fur production. The area of ​​the skin is 40-50 dm2, the thickness at the rump is 1.2-1.4 mm. The skin has a rather thick epidermis (3-4% of the skin thickness). Such small and thin leathers are used for the production of clothing, haberdashery leather and chrome leather for shoe uppers.

Opoek - the skins of suckling calves that have not mastered plant food, with primary non-shedding wool (up to 3 months, regardless of weight). They are characterized by smooth, soft, moiré hair and a smooth feather. The area of ​​the skin is 40-90 dm2, the thickness is uniform over the area and ranges from 1.3-2.5 mm. Characteristic of this type of hide is a thicker papillary layer than that of the skins of adult animals (from 20 to 30%), the thickness of the reticular layer is from 2/3 to 4/5 of the thickness of the dermis.

The papillary layer of the calf consists of thin bundles of fibers, the ligature of which is loosened by the hair bags, sebaceous and sweat glands located in it. The strength of the mold is determined by the well-developed mesh layer. The mold is used to produce chrome leather for shoe uppers. The best leathers are those made from milk milk (fed with milk); The skins of water-fed calves and grass-fed calves produce skins of poorer quality. Opoek produces valuable leather for high-quality clothing and footwear, as it has a smooth and defect-free grain;

The valuable properties of the drink include a small number of lifetime defects.

Outgrowth - the skins of calves that have fully mastered plant food, with transitional hair during molting. Characteristic of the skin of the outgrowth is that the thickness over the area is less uniform than that of the flange, and the presence of slight folds on the collar (milky stripes). Skin area 60--150 dm2, thickness 1.5--3.0 mm, weight up to 10 kg. The outgrowth is used to produce dense chrome leather for shoe uppers.

Cattle skins weighing over 10 kg, in turn, can be divided into light, medium, heavy raw materials - these groups are divided into non-contoured skins of cow, bull, and bull. Depending on age and gender, large cattle raw materials are distinguished:

Half-skin - skins of heifers and bulls with an area of ​​120 to 250 dm2, a thickness of 2.5-3.0 mm or more, weighing from 10 to 13 kg. The structure of the skin is close to the outgrowth, but has a noticeable shading. In addition, the skins of bulls have rough folds on the collar (frizz). Half leather is used to produce chrome leather for shoe uppers, shoe leather and industrial leather.

Goby - skins of gobies with an area of ​​200-270 dm2 and a thickness in the rump area of ​​3-4.5 mm, weighing from 13 to 17 kg. The skin is characterized by strong furrowiness and brownness. In the finished leather, folds on the collar stand out sharply, which prevents the production of chrome leather for the upper from this type of raw material. The bull is used for making yuft and insole leathers.

Bychina - skins of castrated bulls, differs in significant thickness (from 3.5 to 5 mm in the rump and 2.5 mm in the floors), area (300-570 dm2), and weight (light - 17-25 kg, heavy - over 25 kg). This type of raw material is used to produce high-quality sole, saddlery and technical leather, as well as rawhide. Skins of light weights are intended for making yuft.

Bugai - skins of uncastrated bulls with an area of ​​550-600 dm2, thickness from 4-4.5 mm to 6 mm in the collar area. The skin is less valuable than bull skin, as it has a very pronounced furiness.

Yalovka - cow skins. The weight of the skin in a paired state is from 13 kg and above. The skins of non-calving cows are denser, with a uniform thickness over the area, than cows that have calved many times, since they have stretched floors that are weak to tearing (hollowness). Depending on the weight, the cowhide is used to produce leather for shoe uppers (light), yufti (light and medium), saddle leather (medium), sole leather (medium, heavy), technical leather (heavy).

Large raw materials, as a rule, produce less valuable and cheaper leather, since lifetime defects appear on the skin (as a result, grade decreases) and the unevenness of properties over the area increases (i.e. thickness, strength, chemical composition, microstructure, etc.) . Skins have lifetime defects and uneven topographic properties, but they are more preferable compared to heavy weight raw materials.

Raw materials of heavy weights are separated into separate groups, since their processing requires special and more labor-intensive technologies. Heavy skins include skins of mainly old animals with thickened skin tissue. Therefore, this raw material is often subjected to splitting - sawing in thickness into two or three layers. The top layer is called the face split, and the bottom layer is called the melon split. The face split is distinguished by the smoothness of the mesh surface formed from sawing with knives. Split leather is a loose material with uneven thickness and not very durable; velor leather is often made from it.

Bugay skins are distinguished by their high density, great thickness, the presence of rough thickened folds on the collar and uneven properties across the topography. Large skins are characterized by the presence of many defects. In addition, cattle skins of heavy weights are characterized by low strength indicators. This raw material, even if preserved and preserved in good quality, is prone to odor.

Buffalo skins in the collar part have clearly defined furrow folds. They are divided into light, medium and heavy raw materials, similar to cattle hides; almost half of them are subjected to splitting. Large raw materials from yaks and elk have the same weights as cattle hides. Deer skins (150-190 dm2) are used for the production of suede (clothing and footwear). Leather made from deer skins has high softness and sufficient strength.

Camel skins occupy a small share and produce leather of low quality (loose, low-strength), which is used for the production of haberdashery and clothing leathers. Skins are classified by weight: light - 10-17 kg, medium - 17-25 kg, heavy -* over 25 kg.

Horse skins have a thin epidermis (2--3% of the skin thickness). The thermostatic layer is more developed than that of cattle hides and contains a large number of sweat glands. Collagen bundles are thin, the ligature formed by them is loose.

The mesh layer of this type of leather raw material has a different structure depending on the area of ​​the hide. A more dense structure is noted on the lower back, chest and some areas of the back; in other areas the interweaving of fibers is less dense. A distinctive feature of the chemical composition of skins is the presence of skin and subcutaneous fat, which has a low melting point.

Horse skins are divided depending on the weight and age of the animal. Small horse raw materials include foal skins:

Slime - skins of unborn or stillborn foals, unsuitable for fur production; skin area 30--60 dm2, weight 1--2 kg. The skins are thin and therefore used for the production of haberdashery leather.

Foal - the skins of suckling foals that have switched to plant food for foals weighing up to 5 kg, from which shoe and clothing leather is produced; with an area of ​​40-90 dm2 and more. It is a valuable fur raw material. Skins unsuitable for fur production are used for glove husky and chrome leathers.

Marking - young horse skins weighing 5-10 kg and area from 120 to 200 dm2. The thickness of the skin in the hazas is 2-2.5 mm, in the fronts - 1.5-2 mm. It is used for the production of chrome leather and yuft.

Horse meat is the skins of adult animals with an area of ​​up to 400 dm2. The thickness of the skin in the haz area is 2-4 mm, in the front 1.5-3 mm. Horse meat, depending on its thickness, is used to produce chrome leather, yufti, sole and insole leather.

The quality of the resulting leather depends on the breed of animal - the skins of heavyweights have thicker and rougher skin tissue compared to the skins of trotters. Sometimes, when filming, the skins of adult horses are divided into front and haz, and each part of the skin is subsequently processed separately.

Horse hides are processed in rather small quantities - these are the skins of either sick or old animals. The quality of raw materials is generally somewhat worse than that of cattle hides. The properties of the slither-foal are similar to the slither-foal. Foal skins are the most valuable, as they are uniform in properties and have no defects.

The skins of donkeys, mules and hinnies are close in structure to the skins of horses.

Camel skins have a less dense structure compared to cattle skins due to the presence of fine downy hair in the thermostatic layer of the roots.

Goat skins are high-quality leather raw materials. They are used to produce leather for the uppers of fashion men's and women's shoes. The microstructure of the skin is characterized by a thin epidermis (2---3% of the thickness of the skin), approximately the same thickness of the papillary and reticular layers, a small amount of glands and fatty inclusions, as a result of which the papillary layer is less loose than that of sheepskin. The interweaving of collagen fibers is dense, the angle of the plexus is often horizontal, which gives the skin softness. Chrome leathers are produced from goat skins: chevro, goat, lining leather.

Pig skins as leather raw materials are used in significant quantities in Russia and in small quantities in other countries. More than 20 breeds of pigs are bred in our country, which is primarily due to the diversity of climatic and feeding conditions in individual areas. Pork skins have a unique structure. The outer layer of the hide is rough and rough, but has increased abrasion resistance, which is retained in the leather. Pork raw material contains a large amount of fat, so it is difficult to process and produces rather rough or rag-like, soft ruts for all purposes.

The epidermis, due to the weak development of hair, is thick (up to 5% of the thickness of the skin). Bristles, sebaceous and sweat glands and muscles that raise the hair are found throughout the thickness of the skin, especially in its lower layers. Due to the deep penetration of these structural elements into the skin, the dermis of pig skins is not divided into papillary and reticular layers.

The deep penetration of the bristles creates through holes in the dressed leather, making it water permeable. To eliminate this deficiency, special leather treatment is required. Loose leathers are often filled with prepolymers (acrylates, styrene) or powders (magnesium sulfate, talc, starch, etc.). Due to their low price, they are often used for the production of children's shoes and for clothing velor. Pig skins are used to make leather for shoe uppers and insole leathers.

The leather industry uses sheep skins that are unsuitable for making sheepskin and fur products. A feature of sheep skins is the thin epidermis (1.8-1.5% of the thickness of the dermis). The dermis is clearly divided into papillary (thermostatic) and reticular layers, and the thickness of the papillary layer is usually greater than the thickness of the reticular layer (from 50 to 80% of the thickness of the dermis). The papillary layer is loose due to the presence of a large number of hair bags, sebaceous and sweat glands, as well as muscles that lift the hair. The dermis contains a significant amount of fat, which weakens the collagen ligature. These structural features of the hide give leather made from sheepskin low strength, greater ductility, friability, and water permeability. They produce chrome leather (chevrette), haberdashery, clothing and lining leather from sheepskin.

The determination of the grade of skins is started last, after the mass or area, length and fineness of the coat are known. To do this, the skin is placed on a sorting table and carefully examined on both sides. At tanneries and in large procurement offices for identifying

For the detection of defects, special tables with a built-in light source are used to illuminate the skins from below.

There are more than 20 types of defects in leather and fur raw materials taken into account by the standards, and all of them must be identified when assessing the quality of hides. First, the skin is examined from the inner surface, then from the front surface. On the flesh side, filming defects are revealed - holes, snatches, cuts, tears; lifetime defects - fistulas, cuttings of meat and lard. On wet-salted and dry-salted skins, hidden defects are revealed by cleaning the salt from the flesh in suspicious places. On the side of the hair, attention is paid to the faceless parts, horns, bulk, etc. On sheepskins, they check whether the wool is coming out. If there is a trace of wool on fur sheepskins, then it is determined on which part of the staple it is located, keeping in mind that if there is a trace of 1 cm from the base of the hair, the sheepskin is classified as non-standard. The retrace is established organoleptically. The essence of the method is to determine the tensile strength of a bundle of wool fibers when a tensile load is applied to it. To do this, several tufts of wool are selected from the sheepskin, each 5-6 mm wide. The bundle is pinched with the thumb and forefinger of both hands. Then the stretched bundle is struck with the middle finger of the right hand. The strength of the bundle is considered normal if the bundle does not break due to one blow. If, when testing several tufts, a break occurs in the same places, it means that the wool has an overtrace and based on its distance from the base of the staple, a conclusion is drawn about the purpose of the sheepskin.

Hidden defects are revealed by spreading the fur with your hands to examine the front surface of the skin in suspicious places. The grade is determined by the number, area or length and location of defects in accordance with the defect scoring standard established by the standard. When defects are located close to each other, they are measured by the total area occupied, including the distance between them.

To determine the quality of skins of cattle, buffalo, yaks, elk, horses, camels, donkeys and mules, sheep, goats and pigs sorted according to the standard for raw hides, it is advisable to use a summary table (Table 25).

Depending on the type, weight and area, the skins are divided into four groups during sorting, and according to quality - into four grades.

The maximum number of defects is provided for when classifying hides as grades I, II or III, but for IV it is not established; skins of grade IV must have a certain usable area (undamaged by defects), located in one place, a section of usable area for large hides and deer skins must be at least 25% of the skin area, and for pork and small leather raw materials, fur and fur sheepskins - at least 35%. Moreover, the area of ​​useful area located between the defects can have any shape, allowing large parts of leather or fur coat semi-finished products to be cut out of tanned leather or sheepskin for finished products (Fig. 8, 9). If the useful area of ​​the skin, located in one place, is less than the specified dimensions, then the skin is classified as a non-standard raw material - a flap. Non-standard raw materials are divided into two categories: I - raw materials that have preserved the natural contour of the whole skin, except for skins with the defect “keratinization”, widespread over the entire area, such skins are assessed as a contour flap; II - raw materials that have not preserved the appearance of a whole skin, as well as halves and pieces of small pork skins. This also includes skins that are keratinized over the entire area.

Rice. 8. Determination of the useful area of ​​the hide. Sheepskin grade IV, lean over the entire area with the presence of other defects, but having a usable area of ​​more than 35% in one place

Rice. 9. Determination of the useful area of ​​the hide. Non-standard sheepskin (flap), although the intact area is more than 35%, but since it is not located in one place of the skin, it is classified as non-standard

Table 25

Summary table of the division of raw hides into groups and grades

When sorting astrakhan skins, first of all they are divided by type (purebred, mixed breed, astrakhan fur, etc.) and colors. They begin to sort from black astrakhan, which makes up the bulk. Defective skins and those with deformed curls are identified and sorted last. After black, gray, sur and colored astrakhan are sorted separately. Defective astrakhan skins are divided into skins with deformed curls and those obtained from improper removal from lambs or canning. The sorting is completed by determining the quality of karakul and yakhobab. They determine the quality of the hair and the general pattern of curls, the quality of the flesh side and primary processing, take into account the size, determining it by eye or taking measurements of the length and width of the skin. First of all, the silkiness, shine, thickness of the hair, the type and size of curls in length and width, and their distribution over the area of ​​the skin are determined. The skins of valuable varieties are covered with rolled and bobbed curls over the entire area and, in addition, form a beautiful pattern. If such curls are distributed only on parts of the skin, then it loses its beauty, its value decreases and it is classified as a lower grade. When assessing the quality of curls, it should be borne in mind that skins when stored in large piles have heavily dented curls, which can temporarily change their shape. Therefore, before sorting, such skins must rest in a free state.

The peculiarity of sorting gray astrakhan fur is that its color depends on the ratio of the number of white and black hairs in the curls, their length and fineness. White fibers grow faster than black ones, and in the curls of gray karakul they are longer, so the curls of karakul in light colors are larger than in dark gray and black-gray. This also explains the fact that the curls of gray skins are larger in size and less dense than the curls of black astrakhan fur. Various colors of gray astrakhan fur have the following ratio of black and white hair: in light gray skins, white hair is 75-97 % hair, in gray skins - 55-60%; in dark gray, black hair predominates - 65-97%, in black-gray it is about 3%.

The value of gray astrakhan fur is determined mainly by three indicators: uniformity and uniformity of color over the entire area of ​​the skin; the presence of rolled and bobbed curls and their elasticity. The most valuable skins have an even, uniform color, rolled and bobbed curls, which have a fairly high elasticity.

After sorting, when all the initial data are known, the raw materials are priced according to the purchase price list and a bill of lading of the established form is issued for it, in which all quantitative and qualitative indicators and the cost of each skin to be sold to the procurement organization are recorded.