Xinxiang Ceramic Mug Manufacturer, firing is the core part of the production of ceramic mugs, which directly determines the strength, appearance and safety of the mug. Simply put, firing is the transformation of loose clay, glaze and decal paper into a dense ceramic body through high temperature. This process involves complex physical and chemical changes. A little carelessness, ceramic mugs will appear: cracking, deformation, glaze defects, burst flowers and other problems. For ceramic mug factory, the firing stage of the error may cause the kiln scrapped, the whole kiln ceramic mug billet scrapped, the loss of up to tens of thousands of dollars. Therefore, it is important to master the scientific principles and operational details of the firing process.

1. Raw billet and the kiln's scientific matching

In the ceramic mug into the firing stage, the need for adequate preparation. These preparations mainly include: ceramic mug raw blanks, kilns, heat insulation boards and other hardware facilities; engineers, duty technicians, inspectors, etc., but also need to be based on the season, temperature, humidity and other natural factors, to develop a specific firing program such as firing temperature, firing time, lifting time and spreading heat time.

1.1. “Compatibility” of billet and glaze
- Matching coefficients of thermal expansion: the degree of expansion of the billet and glaze when heated must be close. If the coefficient of expansion of the glaze is greater than that of the billet (e.g., if there is too much quartz in the glaze), the glaze will be “cracked” during cooling, resulting in cracks; otherwise, the glaze will flake off.
- Firing temperature matching: high-temperature glaze (1280 ℃) must be matched with high-temperature body (such as high kaolin content of hard clay), low-temperature glaze (800 ℃) can be used in ordinary clay, otherwise the body is not sintered and the glaze has been melted, the cup crumbles when pinched.

1.2. Selection of kiln
- Tunnel kiln: suitable for single-species mass production, but poor temperature control flexibility. The principle is similar to the “assembly line oven”, the use of waste heat to preheat the new cups into the kiln, energy consumption is low.
- Shuttle kiln: suitable for small batch and many varieties, by adjusting the flame distribution of the gas lance (oxidizing flame or reducing flame), special glaze colors can be fired (such as celadon reduction firing).
- Electric kiln: precise temperature control (±5℃), suitable for low-temperature firing of flower paper containing metallic pigments, but the electric wire is easy to wear out under high temperature, and the long-term cost is higher.
These three modes of kilns are chosen according to the specifics of the ceramic mugs to be fired this time. For example, is this time to make samples, small orders, or mass production. Many customers of our factory have also asked why the sample production time is so short, but the real order production time is so long? This is because the choice of kiln is not the same. Tunnel kiln, once into the production of large orders, its production can not be interrupted. One order must be completed before another can be scheduled. So, it seems like the lead time for large shipment production is longer. However, for the ceramic mugs with return orders, we can book the kiln in advance, in which case the production cycle is shortened.

2. Changes of ceramic mugs during the firing process

2.1. Dehydration period (room temperature~300℃) - Ceramic mugs are mainly evaporated cleanly in the preheating period. Raw billets and glazes need to be fired at high temperatures, and the moisture inside the mug is an unsettling factor. It is important to drain the moisture in the preliminary stage to facilitate the stabilization of the shape of the ceramic mug and the melting of the glaze. In the pre-watering stage, the kiln is required to heat up more slowly, exactly how long it takes, but also with the thickness of this ceramic mug, the season and the room temperature to decide. The dehydration stage has a principle of “rather slow, not fast”, rapid heating, which can lead to mug cracking. In the dehydration stage, the treatment of water vapor is also a challenge. Discharge of water vapor can not be allowed to condense again inside the kiln, otherwise, it is easy to cause ceramic mug glaze with “tear”.

2.2. Oxidation period (300 ~ 900 ℃) - ceramic mug in this stage is mainly chemical changes. With low-temperature dehydration, ceramic mug billet began to formally enter the stage of change. This period, the organic matter in the ceramic mug raw billet for carbonization. For example, plant particles such as roots and grass clippings in the clay are burned to produce carbon dioxide. At this time the mug emits black smoke. Sulfides in the raw material are also oxidized. For example, FeS₂ (pyrite) becomes Fe₂O₃ and SO₂ gas, and if not sufficiently oxidized, the glaze will yellow after firing. Oxygen content should be ensured during this period, as the oxygen required for the oxidizing reaction of the raw billet increases. If the oxygen content is insufficient, it will easily lead to the firing of ceramic mugs will appear black spots, smoke and yellowing.

2.3. Bolitization (900°C to the highest temperature) - At this high temperature stage, the clay is officially transformed into ceramic. With the help of high temperature, the quartz in the raw material will undergo some changes, mainly β-quartz becomes α-quartz, and its volume expands by 0.8%; the feldspar in the raw material also melts at 1100℃, and it will turn into a glassy phase to fill the pores of the ceramic body. The glaze also changes at this temperature to a state similar to magma, which evenly covers and fills the surface of the mug as if it were coated with a film. In the high temperature period, the temperature control is very critical, too high or too low temperature can not make the glaze to meet the standard of qualified products. Real-time monitoring of temperature should be carried out during this period. After many ceramic mugs are fired, the glaze feels like snot and is not uniform enough. That's when the temperature is too high during the firing stage.

2.4. Cooling period -- Although the mug has been fired, the cooling period is the last stage, but also the most important one. Otherwise, you may face the “goal kick, the ball flew” embarrassing situation. High-temperature cooling to room temperature can be divided into three stages: fast cooling period (high temperature - 800 ℃), slow cooling period (800-200 ℃), and constant temperature period (200 ℃ - room temperature). The fast cooling period requires rapid cooling, but does not allow the wind to blow directly on the ceramic mug. The rapid cooling is for the solidification of the glaze, and also for the reverse transformation of the quartz, where the α-quartz changes back to β-quartz. Slow cooling period requires a slow cooling speed, and eventually through the constant temperature period temperature drops to 80 ℃ or less, then you can leave the kiln.


3. Precautions for firing ceramic mugs

3.1. ceramic cup billet before putting into the kiln, to mouth down on the heat insulation pad, the cup directly spaced more than 3cm. in the placement of ceramic cups, to check whether the billet has deformation, cracks and other quality problems, quality problems of the cup is not put into the kiln. The reason for placing the mugs with their mouths facing downwards is to avoid dust falling into the mugs in the kiln, and at the same time, it is not easy to deform the mugs during the firing process.

3.2 During the rainy season or when there is a lot of humidity in the air, the kiln should be preheated to remove the moisture, otherwise the mugs will show “tear marks”. In the event of a sudden power failure or gas failure during the firing process, all valves should be closed immediately and the kiln door should not be opened until the gas is restored.

3.3. Cracks in mugs are caused by uneven drying of the billet, residual moisture inside, or too rapid cooling during the cooling period. During the rainy season, the drying time of the billet should be extended, and the cooling time should be extended at the same time.

3.4. When the mouth of the mug is deformed or the body of the mug is deformed, it is caused by the softening of the billet during the high temperature stage due to too rapid heating, which leads to the deformation of the mug body due to gravity. Or because of the uneven thickness of the mouth and body of the mug during the production stage of the billet.

3.5. Pinholes in ceramic mugs. This is caused by the organic matter in the glaze not being burned out. The glaze needs to be filtered through a 200-mesh sieve during the glaze making process. Another reason is that after the glaze is finished and before firing, the glaze is floating. Ceramic mugs need to be dusted with an air gun before entering the kiln to avoid pinholes.


Kiln firing of ceramic mugs is an art, and this technique firing technique was available in ancient China. Historically, earthen kilns were used, along with handmade ceramic products, and this art has been passed down to the present day. Industrialization progressed with various kilns facilitating the mass production of standardized ceramic mugs. In recent years, with the rapid advancement of artificial intelligence and automation technology, the kilns have become more precise and convenient to control. Xinxiang Ceramics Factory has also introduced a number of kilns with the latest technology, automatic billet trimming production lines, automatic glazing production lines and so on. Therefore, we are able to provide customers with the best ceramic coffee mugs with stable quality.