To give clay products additional properties, they are subjected to high temperatures - firing. But the clay firing technology is quite complex and resource-intensive, so I will try to talk about some of the nuances that you may encounter.

Preparing for firing

Before firing the product, it must be thoroughly dried for 2 to 7 days, depending on the size of the product. It is necessary to dry the product away from heating devices, direct sunlight, drafts - that is, to exclude any sudden changes in the environment in which the product is located. At room temperature and in a dark dry, the product will dry evenly.

With uneven drying, the product may crack and its small parts will simply fall off. Insufficient drying will result in firing defects. It is impossible to dry the product.

After the product has dried, you need to carefully inspect it for cracks. If there are any, you can try to cover them with liquid clay, but this does not guarantee the safety of the product during firing. The best option is to prevent the appearance of cracks, and this is obtained with high-quality modeling and competent preparation of clay.

Be sure to check the sound of the whistle - if it disappears or becomes deaf, then it's not too late to try to fix it.

In some situations, during the drying time, a spider can settle in the products (there was a case when he chose one of my whistles), in which case he needs to be moved to a safe place .

The final stage of preparation will be grinding the product. When grinding, fingerprints, various crumbs and bumps may disappear, and the product will acquire a noble appearance. Grinding can be done with sandpaper of small numbers.

Conditions for firing

Temperature. The most important thing in firing is a gradual increase in firing temperature and gradual cooling of the product after firing. In the first two hours, the temperature should not exceed 400 degrees. The temperature range should be between 300-900 degrees Celsius. At lower temperatures, firing will be insufficient and the product will not acquire the necessary properties. At high temperatures, the product can be completely destroyed.

duration. Depending on the size of the product and the firing method, the duration of the process can vary from 8 hours to several days. Very small products can be fired in a short time.

The composition of the material. The firing technology largely depends on the composition of the clay. Natural clay has an admixture of sand and the less sand, the lower the firing temperature. In my practice, there were cases when purchased powdered clay at 750 degrees literally boiled and dried out in the form of a porous sponge. The product was completely destroyed. The composition of the clay should not contain stones and air. If the material is not homogeneous, a break will occur. Since materials of different densities will expand with temperature changes in different ways.

Modeling quality. The main requirement for modeling is the absence of air bubbles in the product. When the temperature rises, the air will expand and will seek an outlet, tearing the product. Therefore, when filling cracks and fastening parts of the product, exclude the possibility of the formation of air capsules.

Firing methods

Firing in a muffle furnace. There are several ways to fire clay products, but the most common is firing in a muffle furnace. This is an electric oven equipped with a temperature control mechanism.

Modern furnaces have automatic firing programs for products of various types, a window for viewing the status of products and other options. Another important characteristic of the muffle furnace is the volume of the chamber. Some swords have a cylindrical chamber in which only small items can be placed, and there are large kilns for firing pottery and sculptures.

Firing at the stake or in a non-electric oven. A rather non-trivial task, primarily due to the fact that there is no way to fully control the temperature. In addition, the stove is rarely heated for eight hours, and it is difficult to sit around the fire for a third of the day. However, if you are still going to - place the product in a container with sand - this will smooth out a sharp rise in temperature.

Roasting at home. A clay product can also be fired on a gas or electric stove, but I warn you - this is quite dangerous and the firing quality will still be far from ideal. To do this, you can take a cast-iron pan with washed dry river sand and put it on fire. From above, you need to carefully install the product and cover it with a fireproof container - a clay pot or pan. The process must be monitored and the room should be regularly ventilated so as not to cause overheating and oversaturation of the air with toxic gases.

Why roasting is needed

During the firing process, the clay gets rid of almost all moisture, so the product becomes much lighter. In addition, clay elements are sintered and turned into a single ceramic ingot, which is resistant to deformation and moisture penetration. Hence the need for roasting.

Fired products are ready for painting, and after painting they are ready for use.

It's important to know

After firing, the clay is not suitable for modeling, as it is no longer clay, but ceramics.

Firing can be done from several times, gradually increasing the temperature limit to achieve optimal results and gain experience.

After the main firing, the product can be coated with a special composition and fired again. When melted, the composition forms a glaze.

During the drying and firing process, the product can be deformed and eventually become smaller than planned. Therefore, when creating a product, it is necessary to take into account the composition of the clay and the purpose of the future product. Clay with a high sand content is less susceptible to compression.

During the firing process, organic compounds will burn out (especially in natural clay) - this can lead to unpleasant odors. It is necessary to be able to ventilate the room.

The readiness of the product can be determined by weight, color and sound. After firing, any colored clay turns red. If it turned black - the product overheated, if it did not change color - it was not burned enough. Fired products have a lighter weight and a sonorous nature. However, whistles during firing can completely lose their sound (irreparably) or, on the contrary, change.

In any case, proper firing of pottery can only be achieved with experience. So keep it up and good luck!

Information about when and where for the first time people began to use milk firing of clay has been lost for centuries. This probably happened in antiquity a little later, after people learned how to fire clay and invented the potter's wheel. If curiosity has awakened and you want to learn more about the steps of mankind from the primitive clay figurine of a rhinoceros to the modern art of ceramics, read. No one can say for sure when and where people came up with the idea of ​​burning pots in milk. Traveling the world and studying the peculiarities of pottery of different peoples, I was convinced that milk roasting technique characteristic only for Russia, in other countries, and even more so on other continents, it is not found.

In Russia, potters have used milk firing since ancient times, but the "dark times" of communism and perestroika practically uprooted knowledge of history and traditions from people's memory, many secrets were forgotten, including pottery. Today we are, in a way, living through the Renaissance and rediscovering the lost secrets of potters. It is not surprising that almost none of the city dwellers are familiar with milkweed ceramics. Visitors to our workshop, coming to our master classes, for the first time see such unusual chocolate-colored and very rich-looking pots made using the milk roasting technique.

Milk firing of clay, despite the external decorativeness - ruddy, rich shades of brown and light gloss, did not appear at all for beauty. He performed an extremely practical function. The fact is that clay after the first scrap firing remains porous, that is, it absorbs water and micro-particles of food. In order to make pottery suitable for storing and eating food and drinks, potters all over the world went to different tricks - glazing, scalding, waxing, and of course, milk firing.

The most reliable way to make clay waterproof is to cover the shard with a vitreous mass - glaze. However, glazing requires a second long firing at a temperature of more than 1000 degrees, which automatically increases the price of the finished product. Glazes for ceramics are also not cheap. But we will talk about working with glazes in the following articles, and now we will get down to practice!

For work we need:

1. Clay products that have passed the first salvage firing. The color of the clay from which you sculpted does not matter. According to my observations, it is better not to decorate white clay in this way, because. milk on a white surface lies with a transparent burnt film and there is little beauty from such special effects.

2. Milk. Aesthetes prefer only village cow milk. But we, city dwellers, do not keep cows in an apartment, so we are not picky and buy any milk with a fat content above 2.5%. Powdered milk is not suitable for milk roasting.

3. A muffle oven, an electric or gas oven, a Russian oven - whoever has what is at hand. The microwave oven will not work.

4. Milk container. The main condition is that your ceramic “things” fit completely “with your head” in it.

5. You may need: cotton rags, potholders, a fireproof stand on which you will put hot ceramics after firing.

And so, let's get started:

1. To begin with, pour milk into a container prepared in advance and “bath” all the ceramics in milk. Of course, initially all clay products must be dry and clean, without traces of grease, wax or paint. The number one task is to allow the milk to be evenly absorbed into the clay shard. If there are a lot of ceramic products for firing, and the container with milk is small, it is better to “bath” the ceramics one by one. . Do not pile on each other a bunch of everything, otherwise it may turn out that somewhere the milk will penetrate well into the pores, but somewhere not, respectively, at the end of the roasting we will get a marriage.

It is enough to hold the product in milk for 2-3 minutes. The less you keep the ceramic in milk, the more transparent the coating will be after firing. If you bathe the shard for too long, the coating may peel off. In the first seconds, after you dip the clay into milk, you can hear a characteristic sound similar to a slight hiss and bubbles will appear on the surface of the milk -

This is a sign that milk, filling the clay pores, displaces air from them.

2. After all the ceramics have gone through the “bathing” procedure, the products should be dried well - a few hours is best, until the milk is completely dry. If you fire a wet product, in most cases the milky coating will simply crack and peel off the ceramic. Milk forms a greasy film on the surface of the clay, which, as the clay dries, from transparent glossy will become white. Already in the process of firing, this greasy coating will become a beautiful and practical coating for our clay items.

3. Here begins the most interesting - milk roasting! Bathed in milk and dried ceramics put in the oven. For firing in the workshop, I use a muffle furnace, and at home I use a conventional oven. Ceramics, like glass, does not like sudden changes in temperature, so it is advisable to load products into a cold oven and only then set the temperature. Milk roasting temperature varies from 300 to 400 degrees. At 300 degrees, the clay acquires a golden color, like a bread crust. If you raise the temperature higher, you can achieve a very beautiful dark chocolate color. At temperatures above 400 degrees, milk simply burns off the surface of the clay.

At the maximum temperature in the oven, ceramics should be kept until the smoke stops coming - this is a sure sign that all organic matter has burned out of the milk. Here everything comes with experience, some milk quickly begins to darken, and some does not give up for a long time.

For me personally milk roasting a very exciting process - every now and then you want to stick your nose into the oven ahead of time and admire the metamorphoses taking place in the oven. Curiosity often leads to the fact that from the air currents of different temperatures that enter the oven along with my nose, completely unpredictable transitions and stains of various shades of brown are formed on the ceramic surface. On the one hand, this can be considered a marriage - the color of the product turned out to be uneven, but I like such “defective” shards much more - you want such beauty on purpose, but you won’t do it! Happy accidents have not been canceled.

When we conduct milk roasting in the workshop, colleagues often drop in on us with questions: “what are you cooking so tasty for?”. The fact is that at a temperature of 150-200 degrees, when milk begins to sinter on a clay shard, a very appetizing smell of freshly baked buns appears. Everyone's bellies are rumbling right there. And when the temperature in the stove reaches 300-400 degrees, you can hear the typical “oh, what is it that is burning there?” - the aromas of muffin change to the typical smell of burnt milk or porridge. Therefore, it is very important that if your workplace is well ventilated or equipped with an exhaust hood - at a temperature of 350 degrees, all organic matter burns out of milk, so the smoke from the stove comes down mercilessly.

Advice: try adding a little sugar to the milk - 2-3 tablespoons per 1 liter. Sugar will additionally clog the pores, as well as give the ceramics a reddish tint! Experiment!

4. After the ceramics have acquired the color you want from golden to dark chocolate, the products can be coated with ganosis, a water-repellent composition based on wax, oil and rosin, while they are still hot. To do this, you will need various rags, potholders and coasters listed above. Details about what ganosis is, how to do it yourself and what it is for, you will learn on the website from the following article.

P. S.

Traditionally, milk roasting used to process ceramic dishes, but I really like to use this method for decorative things - ladies' jewelry, decorative panels, vases, souvenirs. Ceramics that has undergone milk firing acquires an incomparable warmth, you don’t want to let go of it. Glazed pottery does not possess such magic. If you visit our gallery, you will see that in the workshop we use milkweed very often. Our students also appreciated this ancient forgotten technique.

Clay products are a very exciting and interesting process that allows you to reveal your imagination and talent. If you want your clay figures not to lose their shape for a long time, they need to be dried, and then the clay is fired at home, adhering to a certain technology. After all, the long service life of your products will delight you all the time. All your figurines are unique - they only look like themselves.

Material composition

Clay can have a different composition. It directly affects the firing technology. The composition of natural clay includes an admixture of sand. There is such a regularity that the less sand is included in the composition of the clay, the lower the temperature should be when firing products. There are situations when, when using purchased powdered clay, it boils at 750 degrees and then dries up. As a result, the product resembles a porous sponge. In this case, the clay figurine is usually destroyed.

The composition of the clay must be free of air and stones. Never use inhomogeneous materials because an explosion may occur. Since the composition will include materials that have different densities, and they will expand each in their own way, with a change in temperature.

Natural clay is a material of natural origin and often does not undergo additional processing. In nature, you can find clay of various colors, which depends on the presence or absence of certain elements. For example, clay acquires a red color due to the presence of a large amount of iron. And if there are small amounts of iron and titanium oxides in raw clay, then the white color of the material remains even after firing.

Preparing material for firing

Before firing clay, it must be dried. You will spend about a week on this process, depending on the size of the product. It is recommended to dry it in those places where there are no heating devices nearby, and where direct rays of the sun do not fall. The best option is room temperature and a dark, dry place. It is there that the product will dry evenly.

If the clay has dried unevenly, then cracks or chips may form on the product. If it is not dried enough, then the products may have defects after firing. But it is impossible to dry out the clay.

When the product dries, it must be carefully examined for cracks. If they are present, they can be masked with liquid clay, but this does not guarantee that the product will not lose its shape during firing. It is best to prevent cracks from appearing. This can be achieved, it is enough just to properly prepare the clay and mold the product with high quality.

The final stage of preparation is the grinding of the clay figurine. During grinding, fingerprints and bumps are removed, as a result, the products acquire a beautiful and well-groomed appearance. Grinding is carried out with sandpaper.
Another important factor is the quality of the molding. Make sure that there are no air bubbles in the figure during sculpting. When the temperature rises, the air expands and seeks an outlet, as a result of which the product will break. When you fill up cracks or hold together particles, do it very carefully so that air capsules cannot form.

Rules for firing at home

You can burn clay at home. First you need to dry the product, and then burn it in the oven. In this case, it is necessary to smoothly increase the temperature within two hours to 200 degrees. Clay figurines can be placed in a frying pan or cast iron pot. It should be noted that it is impossible to do a full-fledged roasting in the oven, because insufficient temperature, it cannot harden it, but only dry it.

How can you tell if a product is ready?

Very easy, based on color, weight and sound. If the color of the fired clay is black, then the figurine is overheated. If the color has not changed, it means that the product was not burnt enough. Fired colored clay should be red.

Clay firing technology

Clay kiln

The best option for firing clay - it is a muffle furnace . This oven has adjustable temperature. It should be remembered that such a furnace is very expensive and not everyone can afford to buy it. But there is no need to be upset, because it can be replaced with other good appliances, for example, firing clay in the oven. Start firing the clay at 200° for 2 hours. Then, within 6 hours, gradually raise the temperature to 1000 °. This temperature regime allows you to protect the clay product from the appearance of stains and will help maintain a uniform structure.

Clay firing can also be done in barbecue or brick oven . These species are a closed space, which is characterized by a stable temperature. It is needed so that the clay product heats up evenly, and various defects do not form on it, such as surface spreading. The product to be fired must be left until the fuel burns out completely and the firebox cools down. The product should be in the oven for about 4 hours.

Firing a pottery over a fire is a very affordable option. It is used for firing small items. So, take a pottery and place it in a tin vessel, which you have previously heated and made holes on the sides. In most cases, the vessel is an ordinary tin can. Burn the product for about 8 hours, no less.

fire the clay not possible in the microwave. . Such an oven can only remove moisture. Clay products, after you have dried them in the air, are placed in a microwave unit for 3 minutes. This is done to improve their condition.

Temperature regime

The main rule in firing clay products is that you need to gradually raise the firing temperature, and then gradually lower it, giving time to cool the product. At first (the first 2 hours) the temperature should be no more than 400 °. The firing temperature may fluctuate in the range of 200-1000° during firing. If the temperature is lower, then the firing will be insufficient, and the figurine will not have the desired properties. If the temperature is very high, then the figurine may collapse.

Duration

This process can take from eight hours to several days. It depends on the size of the product and the firing technology. If the figure is small, then this can be done as soon as possible.

It's important to know!

• Once the clay has been fired, it is no longer possible to change the product.
• You can do firing more than once, while gradually raising the temperature in order to achieve the optimal result and gain experience.
• When you have completed the main firing, you can apply a special coating to the figurine and then fire it again. This coating will melt and the resulting glaze will form.
• During drying and firing, the figurines can be deformed and decrease in size. That is why when creating a product, the composition of the clay and its future purpose should be taken into account.
• If the clay contains a lot of sand, then the product will be less compressed.
• Also remember that organic compounds burn out during firing, which in turn leads to unpleasant odors. Therefore, it is required that the room be ventilated.

Before fired earthenware must be dried at room temperature for 3-5 days, depending on the size. This evaporates most of the moisture in the clay. If the outside of the product is dry, but moisture remains inside, then it may explode during firing. It also explodes when stones are present in the modeling clay. After firing, clay acquires new qualities - strength, rigidity, durability.

At home, when there is no muffle furnace, products can be fired on a conventional electric or gas stove.

In this lesson, we will use an electric stove.

I use a small frying pan and a cast iron pot for firing my clay products. At the bottom of the pan, pour fine sand for gradual heating. We put the figurine on the sand and cover it with a pot.

The heating temperature must be increased gradually. First, I turn on the minimum heating for 30 minutes, then we increase the temperature to a maximum for 5-6 hours. Before taking out clay figurine you have to wait until it cools down completely.

Clay is a malleable material, fertile ground for experimentation and the creation of various decorations and creations. In order for the resulting products to serve as long as possible and not lose their shape, it is necessary to fire after drying. The process is not easy, it involves following certain rules, taking into account many details. But the result is worth it: the product will please with a long service life, it will not deform or collapse. This article is devoted to the firing of clay products. Read on about the features of the technology, its types, rules and temperature conditions.

Composition of raw materials

Clay is heterogeneous, the amount of impurities in it varies. Depending on their percentage, a certain type of firing and temperature regime are selected. Natural raw materials contain sand, and the less it is, the lower the temperature should be.

The composition should not contain foreign stones or air. Due to the fact that the density of these elements differs from the density of the base material, they will endure the temperature in a different way: they will change their properties and expand at different speeds. In some cases, this may be fraught with an explosion of the product. The presence of certain elements in the composition affects the color of natural clay. So, it becomes red due to the high content of copper. The firing time of the clay varies depending on the composition.

Preparation

Before starting the procedure, the product must be thoroughly dried. Pre-drying is carried out without the participation of heating devices and without direct sunlight on the surface. The best option is a dark, dry place that maintains an average room temperature. It is important that drying takes place evenly. Otherwise, cracks and chips will appear on the surface. The process takes up to a week: depending on the volume of the resulting product. If it is not dried out, defects may form after firing.

There is no such thing as "drying" clay.

After preparation, it is necessary to check whether cracks have formed on the surface. They can be eliminated with liquid clay, but this does not eliminate the risk that the product is deformed in the oven.

The last stage of preparation is grinding, it brings the product to perfect condition. The main tool is sandpaper. With its help, various irregularities, tubercles, fingerprints are eliminated.

Important:

1. The properties of clay change during firing, so after the completion of this process, it will be impossible to change the shape of the product.
2. After drying, the products are deformed, reduced in size.
3. If clay is fired at home, the room must be ventilated. Under the influence of temperature, various organic compounds are released. Some substances have an unpleasant odor and may be toxic.

Clay firing technology

The process takes place in one or more stages. The most popular scheme is a two-stage one. It involves two consecutive firing processes.

Intermediate (scrap) stage. An item without glaze and decor (with the exception of engobe and patterns made with colored clay) enters the oven. After the procedure, the so-called semi-finished product, scrap, is obtained. The choice of temperature regime should be carried out in such a way that a balance of two factors is obtained:

• the product managed to acquire some strength, and all gaseous substances evaporated from the composition. This occurs as a result of the completion of special physical and chemical processes;
• surface porosity should not be completely eliminated. The material must be able to absorb some moisture so that glazes and patterns can be applied to it.

Poured firing (the second stage) is carried out after the glaze is applied to the product and the decor is created. The temperature regime is dictated by the requirements of the materials used: paints, glazes and others.

Types of two-stage firing

1. Porcelain pattern. Basic principle: the oven temperature during the second stage must be higher than during the first. Such a scheme makes it possible to facilitate the decoration process after a not very intensive first firing. The firing temperature of the clay is set in the region of 800-1000°C. If cracks appear on the product, they can be easily identified by the characteristic sound after tapping and eliminated. Glazing is much easier compared to the one-step option. The main properties (strength, resistance, moisture resistance) the product acquires after decoration, during the second stage. This technology is used for porcelain.
2. Faience scheme. The main principle is that the second (watered) stage occurs at lower temperatures than the first. It is used if the structure of the material remains porous after intensive firing or if the glaze requires a low temperature. It is used for faience products: the clay in its composition has a high refractoriness. Temperature regime - 1200-1250°C. The second stage has no temperature restrictions: its value is dictated by the characteristics of the glaze and paint.

The subsequent stages are carried out in cases where it is necessary to fix the decor. They are shorter, in contrast to the two previous stages, and are carried out at lower temperatures.

Firing in one step

Advantages:

• profitable from an economic point of view;
• implies the use of fewer resources.

Flaws:

• a more thorough approach to decorating: due to the fact that the surface is not strong enough, you need to be careful;
• glazing by simple dipping is virtually eliminated. And this method is considered the simplest and most profitable;
• in order to fix the glaze, it is necessary to use special additives.

This method is suitable when:

• long and laborious decoration is not necessary;
• production provides for the percentage of defective units;
• the glaze is high-temperature and its melting period is equal to the clay sintering period;
• if part of the glaze can be applied by spraying.

The firing process takes place in several stages:

1. 25-200°C - the product gradually and slowly heats up, the water between the layers evaporates. The stage is indicative: at this time it is possible to see whether mistakes were made during production and pre-drying. If there were errors, then bubbles, bumps, cracks will appear on the surface. It is important that the heating of the furnace is carried out evenly, too intense or, conversely, a slow increase in temperature is not allowed. The optimum speed is 70-100°C per hour.
2. 200-400°C - at this stage, all the water in the layers should completely evaporate, and most of the organic compounds should be eliminated. The optimum temperature rise rate is 100°C per hour. When the temperature reaches 400°C, it is necessary to take a twenty-minute break in order for all gases to escape and the temperature inside the oven to stabilize.
3. Up to 600°C - water is released, which is included in the crystal lattice of minerals in the composition of clay. The temperature rise rate must not exceed 100°C. After reaching a level of 600 ° C, a half-hour break should be taken.
4. 600-800°C - the temperature should be raised more intensively than usual - by 140-150°C per hour. This is a transitional period, when the old structures have already collapsed, and new ones have not yet had time to form. The material at this temperature is the least durable.
5. 800-1000°C - the beginning of the sintering process and the formation of ceramic compounds. Clay minerals no longer decompose, but begin to interact with other elements, to form new bonds. Diffusion of structures occurs - a chemical process accompanied by the release of gaseous substances. The firing speed should not exceed the range of 75-100°C.
6. Cooling of ceramics most often occurs naturally after the furnace is turned off. Do not open it, letting in colder air - the uniformity of cooling is disturbed.

Firing methods

1. A muffle furnace equipped with a special mechanism that regulates the temperature inside. Often they have special programs for different types of firing.
2. Bonfire / non-electric stove. The product should be placed in a container with sand, then in a fire: this way the effect of sudden heating is minimized.
3. Clay firing at home using a gas or electric oven. The most dangerous method. It is necessary to pour river sand into a cast iron pan, then put the necessary product and cover it with a pan or clay pot. It is important to monitor the process and periodically ventilate the room.

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