River clay. Types and properties of clay materials

We continue to move into the cosmic unknown. The world is increasingly looking like futuristic fiction. Therefore, an essentially unnatural return to simple, natural materials seems so natural.

Another source of the modern desire for naturalness is the permanent fear of environmental collapse. Eco-friendly design is more in demand today than ever. It is today that clay begins to be associated with value, despite persistent historical connotations. Modern design willingly takes clay into use, enthusiastically discovering its incredible decorative and practical potential.

Clay in construction

Clay as a material in modern interiors has a very wide application due to its plasticity. What other material can be equally used both in bulky construction and in the manufacture of the finest crafts?

Clay, varying in composition and properties, can be used almost everywhere today. So, along with the traditional clay! – brick, very popular as building material adobe blocks. Consisting of clay, sand and organic fillers, they have extremely low cost and excellent technical characteristics.

Although modern technology making adobe blocks and differs from the traditional one: instead of straw, as a rule, sawdust is used, and the blocks themselves are made not manually, but mechanically - nevertheless, this material continues to retain the charm of deep antiquity.

Adobe blocks are actively used in construction today, and houses made from them show their best performance, both in terms of technical criteria and aesthetically.

What you need to know to use clay

It is useful to know that in order to use clay yourself, as a building or decorative material, to obtain a satisfactory, high-quality result, it is extremely important to be able to select the composition of the clay. This becomes more obvious if you know, for example, that the building mixtures themselves sometimes contain several types of clays at once, which gives them their qualities.

The Amazing Possibilities of Clay

Clay as a material has truly inexhaustible application possibilities. Known to man since the ancient times of its formation, it still remains relevant. Like thousands of years ago, clay serves our most diverse needs, albeit in a different form than before: instead of unfired dishes, today we have at our disposal both universal earthenware and the finest porcelain; instead of adobe floors - a myriad of slabs and tiles - and so on.

Today, clay is used to make plasters for walls, building mixtures, roofing and facing materials, stucco molding, sculptures, dishes, decorative elements and much more. Despite the spread of innovative materials, clay firmly holds its traditional positions, and even penetrates into the competitor’s camp, constantly discovering new possibilities for its re-actualization.

Walls

Clay plasters are becoming increasingly popular today. The living surface of walls plastered using this material is not only very attractive, but also has many useful properties due to its naturalness and environmental friendliness.
Clay plaster is a hypoallergenic material that acts like a filter. It is able to absorb excess moisture, which helps regulate the microclimate inside the house. It is more than affordable. It is easy to use. It has excellent protective characteristics and is resistant to microcracks, which prevents its destruction.

Floor

Today, there are a number of technologically different ways of making clay. At the same time, the composition and basic properties of these floors are almost identical.

A clay floor is poured or lined with a mixture of clay, sand, straw, crushed stone or other additives. As a result, the floor acquires a smooth surface that is unique in properties and appearance and is resistant to wear. Such floors have antiseptic and antistatic qualities. They help maintain an optimal moisture balance and can contain and even neutralize unpleasant odors. In addition, they have the ability to retain heat: heating up during the day, they gradually release it at night.

It is also important that the surface of a clay floor does not require special maintenance and can be easily repaired if necessary.

Facing

Cladding external walls with clay is not an easy task: clay absorbs well and releases water when wet and heated, which ultimately leads to the formation of cracks. This requires the use of special technologies when processing the finished coating and producing facing materials. In this capacity, clay can be used in the form of ceramic outdoor tiles and plaster mixtures

Walls made of adobe are also not very moisture resistant, so they need additional plastering. For this purpose, lime is traditionally used, which compensates for the natural deficiency of clay blocks and imparts a special charm to the building.

Roof

Traditional ceramic tiles are made by simply firing clay. Despite the simple technology that has not changed since ancient times, such tiles can serve for many decades, sometimes without even needing repair. Manufacturers, as a rule, provide a guarantee for their products for up to 30 years.

Such tiles are not afraid of temperature changes, drying out from direct sun rays, and even open fire and acid rain. The clay roof cools and heats up very slowly, which provides a particularly comfortable climate inside.

When choosing a tile, it is recommended to pay attention to the fact that the pores on its surface must be closed: the more porous the tile, the higher its ability to retain and absorb moisture, which can ultimately lead to its destruction. In addition, the tendency to absorb large volume moisture significantly reduces the frost resistance of clay tiles.

Pottery

Despite the huge number of newfangled materials for making dishes, clay does not lose its position. Products made of ceramics, porcelain, terracotta and faience are still widespread and in demand.

Ceramic cookware does not emit harmful substances when heated. There is no scale in it. It is chemically inert - in a word, ceramics is almost an ideal option for dishes used in our everyday life. Terracotta is made from special red types of clay. After firing, it acquires a characteristic texture, and can be either coarse-grained or fine. The color of terracotta varies from red-brown to creamy flesh.

Today, terracotta is used to make dishes, which was not done before: there was an idea that terracotta does not like water. The development of terracotta production technology has changed the situation, and now many manufacturers have turned to this material in search of new interesting solutions.

Home spa

Clay also has quite extraordinary uses in modern life. Since those ancient times, clay has proven itself not only as a construction or decorative material, but also as a cosmetic product.

Clay tones, disinfects, and whitens the skin. Excellent for preparing hair masks, as it contains a large number of silicon, which promotes the growth and strengthening of the hair follicle.

Although today, by a strange coincidence, clay as a building or decorative material is perceived by us with a slight touch of exoticism or even social disorder, nevertheless, a global fad is increasingly changing this state of affairs.

Every year, projects and ways to use clay become bolder and more interesting. So it is quite possible to expect that after some time the appearance of our homes and cities may change significantly, including thanks to clay.

Clay- a plastic natural material used in construction, folk crafts, treatment and healing of the body and in other areas of human life. It is this widespread use that is determined by certain qualities and properties of clay. And the properties of clay are largely influenced by its composition.

Application of clay

Clay is very accessible, and its benefits are invaluable, and therefore it has been used by people since ancient times. There are many mentions of this wonderful material in history textbooks of all countries of the world.

Construction. Currently, clay is used as a material for making red bricks. Clay of a certain composition is molded and fired using a certain technology to obtain a durable and inexpensive ingot - a brick. And buildings and structures are already being built from brick. In some countries and regions, clay is still used to build houses - mud huts; the use of clay is widespread in the construction of brick ovens, where clay serves as a binder (as cement). The same clay is also used for plastering stoves.

Medicine. Wellness and traditional medicine uses clay in the form of mud baths and masks. The whole point is to nourish the surface of the skin with the beneficial elements of clay. Of course, not all clay will work here.

Souvenirs and dishes. I combine two large directions into one, since many examples of dishes are only of a souvenir nature. Plates, pots, jugs and vases are present in abundance in modern stores. Not a single fair is complete without the sale of clay souvenirs - smoky toys, whistles, signs, keychains and much more. You and I will try to create a lot of things ourselves.

Clay can be included in composition of other materials. Finely ground Chasovoyar clay, for example, is an element of artistic paints (gouache), sauce, pastels and sanguine. Read about this in the "Help to the Artist" articles.

Properties of clay

Color. Clay of various compositions has many shades. The clay is called by its colors: red, blue, white... However, upon drying and further firing, the color can completely change. This is worth paying attention to when working with clay.

Plastic. It was the ability to deform and retain the shape given to it that allowed man to find the use of clay in his everyday life. It is worth noting here that everything depends on the consistency - the ratio of the amount of water, clay and sand. Different jobs require different compositions. So, for sculpting, sand may be completely unnecessary.

Hygroscopicity allows clay to absorb water, changing its viscosity and plasticity properties. But after firing, clay products acquire water resistance, strength and lightness. The development of technology has made it possible to obtain earthenware and porcelain, which are indispensable in the modern world.

Fire resistance. A property used more in construction than in artistic crafts, except for the firing of products. The firing technology is different for a particular clay composition. Closely related to drying and firing is the property of clay shrinkage or compressibility - a change in mass and size due to the removal of part of the water from the composition.

Clay composition

The properties of clay are determined by its chemical composition. Different types of clay have different chemical compositions. For example, red clay contains a lot of iron oxides. Clay basically contains certain substances - clay minerals - which are formed during various natural phenomena. The format of the article does not provide for consideration chemical properties and the composition of the clay, so I won’t go into details.

The composition of clay suitable for use in folk crafts, as already mentioned, is determined by three important elements: clay minerals, water and sand.

The proportions of these elements can be changed, although it is much easier to add than to remove. So, for example, dry clay can be quickly dissolved, however, it is not at all easy to make clay as liquid as sour cream suitable for modeling. Sand is very easy to add, but removing it from the clay is a non-trivial task.

There are “lean” and “fat” clays. The “fat content” scale determines the plasticity coefficient, and the binding properties of clay allow you to regulate the fat content by mixing it with other natural materials, for example, sand. Lean clay has less plasticity, its binding force is weaker, but it shrinks less during drying and firing.

Clay deposits are found in varying states around the world. This ensured its use by artisans of different nationalities, and contributed to the emergence of such a variety of products and technologies.

Craftsmen have learned to control the behavior and condition of clay through various additions to the composition. This way you can thin the clay, elutriate it, give it greater fire resistance, and reduce shrinkage. As a result of such manipulations, an experienced craftsman will be able to ultimately obtain a high-quality, highly artistic product.

Clay has been known to mankind since ancient times and is actively used in economic activity. In our article we want to talk about its types and how clay is extracted.

Origin of clay

Before starting the conversation, I would like to define the breed. What is clay? It is a sedimentary fine-grained rock that has a dust-like structure when dry and plastic when moistened.

It is formed as a result of the destruction of rocks, for example, during the process of weathering. The main source of clay layers is feldspars. It is when they are destroyed under the influence of atmospheric reagents that clay minerals are formed. Sometimes strata are formed through the process of accumulation. But more often this occurs as a result of sediment from water flows. Then accumulations of clay form on the bottom of seas and lakes.

Types of clay

Sedimentary clays are formed as a result of the transport of clay weathering products to a new place and settling there. Based on their origin, such rocks are divided into continental (formed on the mainland) and marine (formed on the seabed).

In turn, marine clays are divided into:

1. Coastal-marine. They form in coastal regions, river deltas and bays. They are characterized by unsorted material. Very often such rocks are interbedded with siltstones, sandstone, and coal seams.
2. Lagoon. Such clays are formed in sea lagoons (desalinated or with a high salt concentration). As a rule, the rocks contain iron sulfides and calcites. Among them there are fire-resistant types.
3. Offshore. Such clays are formed at a depth of no more than 200 meters. They are more homogeneous in composition.

But among the clays of continental origin there are:

1. Diluvial, which are characterized by a mixed composition and its sharp change.
2. Ozernye. Such rocks contain all clay minerals. It is believed that the most best types fireproof types.
3. Proluvial. Such rocks are formed by temporary flows. They are characterized by poor sorting.
4. River species can be found on the terraces of reservoirs, especially in the floodplain. Such rocks are poorly sorted and quickly turn into pebbles and sands.

In addition, residual clays are released. They are formed as a result of weathering of all kinds of rocks on sea or land. Usually they are not very flexible. Continental residual rocks include kaolins and other eluvial clays.

In Russia, the extraction of clay (ancient residual rocks) is quite common in Eastern and Western Siberia, in the Urals.

Is the earth rich in clay?

Clay is found in many regions of the globe. If there is not much black gold and diamonds on Earth, then there is certainly plenty of clay. This is quite natural, since the rock is sedimentary and, in fact, is stones worn out by time and external factors, crushed to a powder state. Clay is home to a variety of organisms that affect its color. Iron salts play an important role in the coloring of the mineral. In nature, there are pink, green, blue, yellow, red and other clays.

In the old days, clay mining was carried out along the banks of lakes and rivers. They also dug special pits for mining. Then it became easier to purchase the mineral from a potter than to mine it yourself. Of course, extracting red clay is not a difficult task. But, for example, noble white previously could only be purchased in special stores for artists. Currently, you can purchase the mineral in the form of a cosmetic product in any store. Of course, such clay is not sold in its pure form, but with all sorts of additives.

Clay meets us in Everyday life almost every day. Field paths and paths are covered with a layer of dust in the heat; in the rain they turn limp, like slurry, because there are minerals here too.

Properties of clay

The widespread extraction of clay (photos are given in the article) is directly related to its properties, since it has long been used by people for a variety of purposes. When dry, it absorbs water perfectly, and when wet, it does not allow moisture to pass through at all. As a result of mixing and kneading, clay is able to accept the most different shapes, preserving them even after drying. This property is called plasticity.

In addition, clay has good binding ability with solid and powdery bodies. As a result of mixing with sand, a plastic mass is obtained. However, its plasticity decreases with increasing sand and water content in the mixture.

"Skinny" and "fat" varieties

Clays are divided into “lean” and “fat”. The latter have a high degree of plasticity. And they got the name “fat” because when soaked they seem greasy to the touch. This clay is slippery and shiny, it contains few impurities.

The extraction of sand and clay is always inextricably linked, since, as a rule, a mixture of them is used. For example, when producing bricks from fatty clay, many cracks form during firing. To avoid such unpleasant moments, sand (sometimes sawdust, brick fragments) is added to the clay.

Minerals that are not plastic or have low plasticity are called “lean.” They are rough to the touch and have a matte surface. When rubbed, such clay easily crumbles, since it contains a lot of impurities. A brick made from such a mineral is not durable.

A very important property of clay is its relationship to firing. As you know, when soaked, it hardens in the sun. However, it can be easily crushed into dust. But after firing, the clay changes its internal structure. At very high temperatures clay can even melt. It is the melting temperature that characterizes fireproof properties substances. Different varieties Clays have completely different refractory properties. There are types of minerals that require enormous heat for firing (about 2000 degrees). Such temperatures are difficult to achieve even in factory conditions, so there is a need to reduce fire resistance. This can be achieved by introducing additives (lime, iron oxide, magnesia). They are called fluxes.

Clay has different colors (white, yellow, bluish, brown, red, etc.). The quality of the brick in no way depends on the shade of the mineral.

Use of clay for medicinal purposes

Some types of clay are used in medicinal purposes. White is used to treat obesity, intestinal diseases, hair loss, and strengthen nails. Red is used for cardiovascular diseases, varicose veins, hypotension, endocrine and nervous diseases. Yellow clay helps with osteochondrosis, headaches, problems with the intestines and stomach.

Black is used to lower temperature, treat inflammatory skin diseases, and rejuvenate the body. But blue clay is used to treat obesity, hypothyroidism, relieve muscle weakness and improve joint mobility. In cosmetology, this type of clay is used for oily skin.

Industrial Applications

Clay is actively used in industry: in production ceramic tableware, tiles, earthenware and porcelain sanitary ware. The mineral is no less in demand in construction. Clay is used in the production of bricks, building materials and expanded clay. It is also the basis for all brick and pottery production. When mixed with water, clay forms a plastic dough-like mass that can be processed. The initial properties of raw materials can vary significantly depending on the place of origin.

Natural red clay owes its color to the presence of iron oxide in its composition. When fired, depending on the type of kiln, it may acquire a whitish or red tint. It is actively used for making small sculptures.

White clay is quite common in the world. When wet, it has a light gray color. But after firing it acquires a noble shade of ivory. This type incredibly plastic due to the absence of iron oxide in the composition. White clay is used to make tiles, dishes, plumbing fixtures, and crafts.

Used for the production of porcelain items special kind clay, which contains quartz, kaolin and feldspar, but iron oxide, on the contrary, is absent. When wet, the mineral has a light gray tint, but after firing it becomes White color.

Clay: extraction method

There are the most different ways mineral extraction. It all depends on the volume of inventory and location. As you know, there are quarries for clay extraction, in which the extraction of minerals from the massif is carried out by gear hobbing machines or excavators.

For large volumes of rocks, especially if work is carried out in winter time, use the explosive method. The extraction of clay and kaolin (blue, white clay) in conditions of high quarry humidity or in kaolin factories is carried out using hydraulic monitors.

For ceramic enterprises, the rock is mined in specially designed quarries, after which it is transported by rail and road to its destination. As a rule, several types of clays occur in a rock layer. Each variety is removed separately.

Place of Birth

Natural accumulations of rocks are called deposits. The territory of Russia is rich in reserves of various types of clays. For the ceramic industry, deposits of pure rocks that contain few impurities are of great interest. They belong to kaolin and refractory clays. Mining of ordinary (light-melting) varieties in Russia is carried out almost everywhere. But deposits of refractory and blue clay are much less common.

Clay mining in Russia is carried out in such deposits as Kashtymskoye, Nevyanskoye, Astafievskoye, Palevskoye. Each of them has its own characteristics depending on the conditions of formation, chemical and mineral composition.

Deposits of fire-resistant species are much more common than kaolin deposits. But at the same time, the most numerous are the places where refractory varieties are adjacent to fire-resistant ones. In Russia, the most famous among them are the Troshkovskoye, Latnenskoye and Gzhelskoye deposits.

But the main places for bentonite production are the Gumbrian, Aksan and Oglalinskoye deposits.

The location for clay extraction is always selected depending on the quality of the raw materials, the volume of reserves and the economic benefits of their development.

Instead of an afterword

Since ancient times, people have used the properties of clay for their own purposes. Its extensive reserves make it possible to use it without hesitation in various industries and in everyday life.

The art of making vessels and other household items from clay can be considered the most ancient, becoming one of the first types technical production. What could be more ordinary than clay! Meanwhile, its role in people’s lives is great and is associated with its unusual properties. The observant mind of man drew attention to them in ancient times. Clay fired in a fire is the first artificial material produced by man. The properties of this material were gradually revealed to man. Until now, a third of humanity lives in mud huts. And this is not counting the houses made of baked bricks. Not only walls are made from clay, but also hearths and roofs. To increase the strength of such an adobe floor, it is watered with salt water from time to time. Cuneiform writing, which first appeared in Mesopotamia, was pressed onto thin clay tablets. And the complex composition of modern paper necessarily includes white clay.

Clay has been used since ancient times as a remedy. Sprained hilus was treated with a plaster of yellow clay diluted in vinegar. And for pain in the lower back and joints, clay diluted with hot water with the addition of kerosene was applied to the sore spots. Healers preferred to use oven clay when performing divination. She was treated for the evil eye and fever. Small clay pots (makhotkas) were placed on the body for colds as medical jars. They even did “brick inhalations” by heating a brick, pouring onion skins on top of it, and inhaling the smoke. And by sprinkling such a brick with wormwood or juniper, they scared away flies and mosquitoes.

They even ate clay. Residents of the North still eat “earth fat” - white clay. They eat it with reindeer milk or add it to meat broth. And in Europe they made delicacies like candies from clay. There is an old Russian riddle: “I was on a kopanets, I was on a topavda, I was on a circle, I was on a fire, I was on a scald. When he was young. then he fed people, and the old flock began to swaddle.” Until recently, any villager would have quickly figured it out. This is an ordinary stove pot. And the riddle itself tells it in detail “ life path" “Kopantsy” in Russian villages was the name given to the pits where clay was mined. The potters respectfully spoke of her: “alive.” “Living raft” found in nature is so diverse in composition that you can find ready mixture for the manufacture of any type of ceramics.
Naturally, if deposits of valuable types of clay are found, then pottery production quickly grows around them. This, for example, happened in Gzhel near Moscow, where white clay was found.

Clay, unlike sand, which filters moisture, absorbs it completely, without allowing it to pass deeper. When mixed with water, clay becomes a plastic “dough” that can be molded into any shape. Having dried, it retains the shape given to the “dough” and after firing it becomes hard as stone. Clay is a product of rock destruction. The process of clay formation occurs constantly, but there was a time when clay formation took place on a gigantic scale. This phenomenon applies to time immemorial, to the glacial and diluvial periods, when the mechanical part of the work of rock destruction was carried out by glaciers moving into the plain. Any clay contains alumina, i.e. aluminum oxide, and silica, and minor impurities can be various alkalis, lime, magnesia, iron oxides and titanic acid.

There are clays consisting predominantly of one mineral (for example, kaolinite refractory clays - kaolins), but much more often they are polymineral, being a mixture of the minerals kaolinite, halloysite and montmorillonite. The rocks that preceded the clays consisted mainly of feldspars and micas. Spars are found in all three types of rocks on Earth - igneous, metamorphic and sedimentary. Solidified magmas - granites, pegmatites - are the ancestors of the clay mineral kaolinite. Halloysite was usually preceded by diabase and gabbro; montmorillonite is a product of the decomposition of volcanic ash, tuff and lava. Over the course of thousands of years, the parent rocks of the clays have been destroyed, decomposed, weathered, turning into fragments, screes and, finally, into tiny particles. Sometimes they remained at the place of their formation.

This is how “primary” and “residual” clay deposits appeared, usually thick (up to a hundred meters or more), occupying significant areas. They are mainly composed of kaolin ("Kaolin" is a corruption of the Chinese words "gao ling", i.e. " high hill"; this is the name of the village in China where they first began to mine these clays). From these clays, which form a light-colored shard when fired, they make fine ceramics - porcelain and earthenware. But more often, rivers, winds, and moving glaciers carry clay materials over long distances. Gradually they settle in stagnant waters. The settled silt layers are homogeneous in their structure. Along the way, they are subject to natural “eluting”, enrichment, and liberation from undecomposed rocks and impurities. Such deposits (the majority of them) are layered, their thickness is relatively small, the area of ​​occurrence is different.

These ubiquitous, shallow Quaternary clays are commonly used to make pottery and building bricks. ??Sometimes clay particles manage to avoid encounters with water flows containing substances that usually pollute clay. In this case, deposits of pure, highly refractory, low-iron clays are formed. They are used for ceramic products with special properties, used in special industries. Climatic zonation has been revealed in both ancient and modern deposits of clay minerals. In the icy Arctic zone, minerals such as hydromica and chlorite predominate; in the moderately humid, cold zone - montmorillonite; in the tropical zone - kaolinite. Scientists have discovered another amazing property of baked clay. It was discovered that during the firing of clay products they become magnetized, recording the features of the Earth's geomagnetic field at that moment in time. Knowing the geomagnetic field of our planet in ancient times, the age of ceramics can be determined with an accuracy of twenty-five years. Archaeologists are helped in this by petrography, microscopy, spectral analysis, x-ray.

Pliny the Elder in the 1st century. n. e. in his “Natural History” he distinguished white clay (argilla) from ordinary, ordinary clay (lutum) and from just soil (terra). In ancient Greek, the word "keramos" originally meant clay; it is mentioned by Homer in the Iliad (8th century BC). In the Old Slavic language there was no word “clay”, but there was a word “Brnie”, meaning clay mixed with water, which is probably where the name of the Czech city Brno comes from. The concept of "potter" in ancient Slavic was denoted by the word "zdun", the root "zd" still forms such words as creator, create, building. The word “clay” has a later origin, probably from the word “clay” - alumina (aluminum oxide), which is part of any clay. Clay on our planet appeared a long time ago, during the interglacial period, which was accompanied for many millennia by the melting of the ice cover, which was up to 2 km thick in Europe. The melting caused powerful water flows, which did the work of clay. They elutriated, moved and redeposited clay and sand, which led to their mixing. These processes are associated with the formation of numerous clay deposits in Europe, particularly in Russia. various properties, which is not observed on other continents.

If you approach clay with scientific point view, then it is dispersed, that is, consisting of solid particles of different sizes, sedimentary rock plate minerals, according to chemical composition- hydroaluminosilicates, and accompanying impurities of other minerals. Well, it’s clear what “hydro” is, “aluminum” probably too, and silicates are compounds of silicon with oxygen. Lamellar minerals, when interacting with water, make the clay plastic, capable of molding and maintaining its given shape when dried. Trace minerals such as quartz (sand), carbonates (chalk, marble, limestone, dolomite, magnesite) and feldspar (the most common feldspathic rocks are granites) are non-plastic, and their presence “thins” the clay, reducing its plasticity. There are a number of classifications of clays according to their chemical and mineralogical composition, origin, and application, but none of them covers the entire set of characteristics useful in determining the suitability of clay raw materials for a particular production.

Division of clays accepted in geology:
a) transported by water, glacier, wind (secondary deposited);
b) formations remaining in place (primary clays);
c) metamorphosed rock-like rocks.
In the classification scheme according to GOST 9169-59, clay raw materials are divided into four groups: kaolins, clays, crackers (refractory stone-like clays) and shale clays (poorly soaked in water). These groups are divided into subgroups:
a) by the content of aluminum oxide in the calcined state (more than 40% - highly basic, from 40 to 30% - basic, from 30 to 15% - semi-acid, less than 15% - acidic);
b) by fire resistance (fireproof - melting at temperatures from 1580°C and above; refractory - melting from 1580 to 1350°C, and low-melting - melting below 1350°C);
c) according to the degree of cohesion or plasticity (forming moldable dough with the addition of normal sand: more than 50% are binders, from 50 to 20% are plastic, less than 20% are lean; do not form dough at all).

Along with those considered, there is an industrial classification of clays, based on their assessment based on a combination of certain characteristics, such as color and appearance after firing, sintering-melting interval, strength of the product upon impact, resistance to sudden changes in temperature. These characteristics determine the industrial purpose and name of the clays. Already in the Middle Ages, names of clays such as brick, pipe, tile, pottery, earthenware, white-burning, clinker and others were developed and still exist. At that time, clays, by the way, were assessed only by touch, and their properties could be assessed by medieval masters. And now, I think, it is not a sin to return to such an assessment of clay, since direct contact with the material at the very beginning of the work unites the master and the clay into one whole, allows them to feel each other, for if the tool is an extension of the potter’s hands, then the product is an extension of his soul. So, the clay used in pottery must be heavy, oily, elastic, in general, with a solid character - it must keep its shape. The color of clay can be red, brown, blue, green, gray or white. Sometimes clays of chocolate color (so-called snickers) or dirty black are found. But I don’t recommend dealing with them, because when fired, organic impurities, a large amount of which gives them a dark color, give off such a spirit that you can take away the saints. The color of clay comes from aluminum oxide, iron oxide and titanium oxide. If the total amount of iron and titanium oxides does not exceed 1 percent, then the clay is white even after firing, but if there are more than 1 percent, then the clay after firing is red, despite the fact that in its raw form it is green or blue.

Quartz (sand) is usually present in clay deposits in the form of rounded, colorless or colored grains. Its amount in clays can vary - from several percent to several tens of percent. The sand that is added to pottery clays to thin them must be ground (otherwise the clay will rub your hands like sandpaper), and its amount should not exceed 25 percent (optimally 15%). As ground sand is added (up to 15%), the plasticity of pottery clay increases; further addition of sand reduces the plasticity. The amount of sand in clay also affects the shrinkage of the product during firing. Therefore, if you want to reduce the shrinkage of clay during drying, which in turn will reduce unnecessary deformation of products and save you from insidious cracks at the bottom of vessels large diameter, then add up to 25 percent sand or ground fired shards to the clay. IN Ancient Greece, for example, grus was added to the clay, which was nothing more than crushed granite. Very often, especially in low-quality clays, there are impurities of calcium and magnesium carbonates (chalk and dolomite) in the form of large and small grains. They are useful and harmful at the same time. I will say a few words about the dual role of these impurities during the firing of ceramics. In a finely dispersed state, these impurities are strong fluxes (additives that reduce the sintering temperature), but at the same time, at firing temperatures up to 1000°C, they reduce the strength of the ceramics, and at higher temperatures, deformation of the products is observed. The chalk content in pottery clay can reach 25 percent, but it requires even distribution and very fine grinding. If carbonates are present in the clay in the form of large inclusions, then the oxides of calcium and magnesium remaining after firing begin to absorb moisture from the air, form hydroxides, increase in volume and ultimately can rupture the product. These harmful inclusions are called "dutik".

Quite common impurities in clay are gypsum and pyrite. They are noticeable after firing in the form of small black “flies”. Pyrite in clay is crystals with a metallic yellowish sheen; gypsum sometimes forms visible to the eye accumulations of large crystals. They can only be removed manually. Harmful impurities in clays are also soluble salts - sulfates and chlorides, which form so-called efflorescences on products. Soluble salts appear in the form of a salt coating on the surface of fired clay products. To combat “efflorescence,” it is recommended to add barium carbonate to the clay composition. In a small pottery workshop it is better to deal with this problem correct mode firing "Efflorescence" is formed mainly at temperatures of 400-500°C, so it is recommended to quickly raise the temperature to 600°C. In some cases, the presence of carbonaceous materials in clay and recovery firing in the range of 700-800°C will be suitable for the decomposition of “efflorescences”.

Organic impurities, as a rule, burn out during firing and leave almost no traces on the surface of the products, except for small shells formed during the combustion of wood particles. (But this property is used when decorating products. For example, inclusions of grains of rice, wheat or even peas in the surface of products after firing will leave a characteristic mark.) A large amount of organic carbon in clay can create a local reducing environment during firing, which promotes earlier sintering clay and with a thick layer (brick, for example) can give the shard local deformation and undesirable coloring. The composition and pottery qualities of the clay are finally determined only after the production and firing of a test product. The easiest way is to purchase clay at a specialized factory or directly in a quarry of some deposit. At factories it is sold in two types: quarry - brought directly from the mining site, which means it requires appropriate processing, or in powder. The powder is a mixture ready for use. All that remains is to cover it with water. Powder, of course, is more expensive, but by purchasing it, you will save time on cleaning the clay. The clay powder purchased from factories producing ceramic tiles and bricks contains 10-12 percent ground glass, which will give strength to future products. But the pottery properties of clay made from such powder are somewhat reduced due to the presence of the same glass.

Currently in major cities organizations appeared selling ready-made pottery clay. There you can buy clay of any composition, small and large fireclay, gypsum, ready-made glaze and other materials necessary for a potter. But if this is not possible, then the necessary clay can, in principle, be found anywhere, for example, on a steep hillside. Clay can even be found on the side of roads or, best of all, along the banks of swamps or small bodies of water, which are formed because rain or spring water falls into a clay bowl. The required clay (usually blue or green) lies either immediately under the turf, or at a depth in a layer of varying thickness. This clay, like quarry clay, requires careful preparation. It needs to be dried, first broken into small pieces. Sufficient time must be spent on this drying. When the clay is completely dry, fill it with water, preferably hot. So much water is needed so that only isolated islands of clay remain on its surface. After swelling, the mass should be laid out on a table covered with canvas or any other rough cloth. Wait until the clay is freed from excess water and will acquire the humidity necessary for work. When drying the clay, it must be periodically turned over and, preferably, kneaded.

The main quality of pottery clay is that it must be clean, that is, not have any inclusions. Of course, some result can be achieved using any clay, but it is unlikely that the products will be of high quality. U good master a small pebble or even a large grain of sand can be commensurate with the thickness of the vessel wall and interfere with the work. You can clean pottery clay by hand (which is unproductive, but quite possible at home) or by pressing it in a plastic state through a fine mesh, as if imitating an industrial filter press. You can also soak the clay in a barrel for purification, that is, dilute it to a slip (the state of liquid sour cream) and wait for large, heavy inclusions to settle to the bottom. After which the pure fraction is drained, making a hole in the barrel at the level of the beginning of the pure slip, and dried to the desired state.

Now we need to talk a little more about the relationship between clay and water. Despite the fact that their characters are similar, it is very easy to quarrel between them, and then you won’t expect anything good. If you overdo it and add too much water when mixing the clay, it will be difficult to remove. The clay dough will be uneven, with lumps. Clay, being a hygroscopic substance, adsorbs moisture from the air, is wetted by water and is capable of swelling in a state of strong watering. Moisture adsorbed by clay is called tightly bound water, in contrast to loosely bound water, which is more freely located between clay particles, more mobile and squeezed out of the clay during compression. Strongly bound water makes up 0.8-1.0 percent of the moisture content of kaolin, freezes at temperatures well below zero, and almost does not conduct electric current. Strongly bound water naturally turns into loosely bound water, which becomes more abundant the closer the state of the clay approaches the working water content, that is, to the state of clay and water when the clay mass exhibits the optimum of its plasticity and its ability to be molded. With the correct moisture content, the clay mass does not stick to the back of the hand. This working water content varies for different clays; for example, in loess it is 18-20 percent, in kaolin - 28-31 percent, in spondylic clay - 31-33 percent, in Chas-Yarskaya - 30-32 percent, in Troshkovskaya - 30-36 percent. With a further increase in water content, the clay loses its ability to maintain its shape and begins to flow like a viscous liquid.

This information about the properties of clay is quite enough to start working with it. In general, we can talk about the properties of clay for a very long time; there are more than thirty names of clays alone, and each of them has a dozen combinations with various additives. When the clay is freed from excess water and acquires the moisture necessary for work, that is, it will knead with effort in your hands, it must be kneaded properly and placed in a plastic bag, and the bag in a barrel with a tight lid, where it should lie for a while before starting work. less than a day, or better - several days. However, clay can remain in a barrel for a long time - all the time until you use it up. To mince clay, many craftsmen adapt various mechanisms, such as industrial meat grinders. Similar “mechanization” can be used at other stages of clay preparation. And still very important point. Just before you start working with clay, you need to knead it thoroughly again, tearing the lump of clay into two parts and forcefully connecting them back. In this way you can free yourself from most of the air - the last and most insidious enemy of the potter. Firstly, when pulling a vessel on a pottery wheel, your hands will fall into air pockets, and you can tear the product or tear it off the wheel. And secondly, the air pockets remaining in the clay can rupture the product during firing, since air, as is known, expands when heated. IN industrial production are freed from air using a vacuum press.

Clay is a sedimentary rock that has a fine-grained structure. This is a very interesting type of rock in its properties, because in a dry state it is crumbly and looks like dust, but when moistened it is soft and plastic, capable of taking any given shape. When it hardens after moistening, the clay becomes surprisingly strong and durable.

Clay is a sedimentary rock that is a secondary product earth's crust, which was formed as a result of the destruction of rocks through weathering.

The most important source for the formation of clay is feldspar, which in the process of decomposition under the influence atmospheric precipitation forms kaolinite and other constituent parts of clays.

Minerals in clays

Clay contains one or more minerals from the group of kaolinite, montmorillonite, or other layered clay minerals. Clay may also contain carbonate and sand particles.

Depending on the quantity and quality of the minerals that make up the clay, this mineral can be the most different colors and shades - light yellow, orange, reddish brown, gray, white and many others.

Different types of clay contain the following minerals:

• kaolinite
• andalusite
• montmorillonite
• halloysite
• muscovite
• hydrargillite
• nacrite
• diaspora
• pyrophyllite
• corundum
• monothermite

There are also some types of minerals that contaminate clays. Among them are the following:

• quartz
• calcium
• dolomite
• glauconite
• limonite
• magnetite
• marcosite
• rutile
• pyrite
• serpentine
• siderite

Properties of clay

Among the main characteristic properties clays can be called the following:

1. High level of ductility
2. Ability to take any given shape
3. Fireproof properties
4. Air and thermal shrinkability
5. Excellent sinterability
6. Viscosity of clays of various grades
7. Degree of shrinkage
8. Clay porosity
9. Swelling of clays
10. Density
11. Waterproof

Types of clay

There are several types of clays, including the following:

• Kaolin- this is the name of the famous white clay, which is used to produce beautiful porcelain and fireproof products.
• Construction clay- used for preparing solutions that are used in the process of constructing structures for various purposes.
• Shale- used in the cement production process.
• Fire-clay- Suitable for the manufacture of refractory bricks and other heat-resistant products.
• Bentonite- when immersed in water, it increases in volume several times, used in drilling fluids in the process well drilling.
• Smectite- has bleaching and filtering properties. Filters made from cloth clay are widely used to remove impurities from petroleum products, as well as various types of oils - both edible and technical.
• Pottery(lump) clay is used in the process of making pottery.
• - used as a medicinal and cosmetic product for applying masks to the face and body.
• Sandstone clay- used for making dishes, decorative ceramics and souvenirs.

Scope of application of clay

After connecting with the right amount With water, clay is capable of forming a dough-like mass with plastic properties. Depending on the location of the deposit of this natural raw material, clay is characterized by different quality indicators. Therefore, it is used for various purposes. Among the areas of application of various types of clay are the following:

• Ceramics production- one of the most important areas of application of clay. Of the various varieties of this natural material make excellent examples of ceramic ware, earthenware, etc. The art of pottery dates back several thousand years, and continues to improve today.

• Manufacturing of building materials— clay is widely used in production. Today, the vast majority of brick products are produced in factories, but there is also an artisanal method of hand-molding bricks, which is successfully used in some regions.

• Cement production— a mixture of clay (25%) and limestone (75%) is used to make cement. During the production process, the raw materials are carefully crushed and then thoroughly mixed. In this case, a strict dosage of components must be observed, otherwise the result will be of poor quality.

• Technical ceramics represents a fairly extensive group of special ceramic products made from a plastic mass, the basis of which is clay. technical purpose widely used in various areas life and human activity - in the form of sanitary ceramics, as insulators electric current in instruments and wiring, and in many other areas.

• adobe construction— adobe buildings are architectural structures, the main material for the construction of which is clay. Mud houses are one of the first examples of ancient architecture. However, the methods of using clay may be different. Thus, the clay mass can be compacted into a mold made of wooden planks, or the clay can be mixed with crushed straw and the board base can be covered with this mixture.

• Medicine and cosmetology— Clay has long been widely used for medicinal and cosmetic purposes. Clay is included in some medicinal ointments, as well as sorbents and preparations for getting rid of diarrhea. And in cosmetology, clay is used to make masks for the face and body, and also includes it in some creams.

• Edible clay- Some types of clay are edible and are eaten. Edible clay is a special additive to the basic human diet, and is a valuable source mineral salts and microelements. Edible clay serves as a sorbent natural origin, which helps cleanse the human body of waste deposits and harmful toxins. At the same time, clay has an enveloping effect and can be used as a natural antiseptic.