Detailed explanation of the brushing glaze process for ceramic mugs

Xin xiang ceramic mug manufacturer, brushing glaze is an important process in glazing ceramic mugs. This process is characterized by high flexibility and a long history of use. In some cases, it is necessary to use the brushing glaze process when glazing mugs. However, this process requires high technical skills and has high production costs.

1. What is glazing?

Glazing, as the name suggests, is a method of “brushing” glaze onto the surface of a ceramic body with a brush (similar to a calligraphy brush or paintbrush). We have seen furniture being painted, but this is ceramic glaze being applied to ceramic mugs. It is one of the oldest, most direct, and most flexible methods of glazing. Unlike “dip glazing,” which involves immersing the entire body in glaze slurry, or “spray glazing,” which requires advanced equipment, brush glazing is akin to an artist painting a picture, applying the glaze layer by layer.

2. Applications of brush glazing

Brushing glaze is done by hand, so it is inefficient but highly flexible. Therefore, brushing glaze is suitable for ceramic mugs that are not produced in large quantities and for small orders. Because brushing glaze is highly flexible, this process is also suitable for ceramic mugs with complex glaze requirements, such as ceramic mugs with handles and bodies of different colors, or ceramic mugs with gradient colors on the body or handle. Brush glazing is also suitable for ceramic cups with multiple layers of glaze. For example, ceramic cups with wood grain, floral patterns, stone patterns, etc. on parts of the cup body, or ceramic cups with glitter glaze. Because brush glazing is usually done with a brush or paintbrush, it is also very suitable for repairing areas where glaze has been smeared or sprayed (such as the handle connection, cup rim, cup bottom, etc.). In addition, the brush glazing process is often used for complex mug shapes. For example, the brush glazing process is used for mugs that are too large, too small, or have complex shapes.

3. What is the brush glazing process?

3.1. Prepare the glaze slurry: Mix the glaze powder and water in a specific ratio and stir to a consistency similar to thick cream or yogurt. If the mixture is too thin, it may flow unevenly; if too thick, it may be difficult to apply and leave heavy brush marks. “Instructions for Making Glaze in Ceramic Mugs”

3.2. Prepare the body: Make sure that the mug body waiting to be glazed is completely dry (called “raw body”) and that the surface is clean and free of dust and oil stains. Typically, they undergo a “plain firing” process (What is the plain firing process for raw ceramic mugs? ) to make them sturdy and less prone to breakage, making it easier to absorb water (better glaze adhesion).

3.3. Glazing steps:

Glazing technicians hold a brush (commonly a wool brush or soft-bristle brush) and dip it into an appropriate amount of glaze slurry. Like painting, the glaze is evenly applied to the surface of the body. The direction of brushing should be consistent or cross-brushed to ensure full coverage. For mugs, pay special attention to the rim, the connection between the handle and the body, and the bottom rim, which are areas where glaze is easily missed or accumulated. Both the outer surface and inner cavity of the mug need to be carefully brushed. The glazing process usually requires 2-3 coats or even more to achieve the desired glaze thickness and even coverage. During multiple glazing applications, pay attention to the time intervals: After applying the first layer (base glaze), wait until the surface is slightly dry before applying the second layer. If the glaze surface is too wet when applying the second layer, it may damage the first layer, resulting in uneven glaze or peeling.

After glazing is complete, the ceramic mugs should be inspected and repaired: Carefully check whether the glaze surface of the ceramic mugs is uniform, and whether there are any missed spots, bubbles, or obvious brush marks. If there are any problems, repair them with a pen in a timely manner. Finally, place the glazed mugs on a drying rack to dry naturally, avoid touching them, and wait for them to be fired in the kiln. “In-depth analysis of the firing process of ceramic mugs” .

4. Pre-glazing and post-glazing work

4.1. Pre-glazing preparation:

Body preparation: Ensure that the green body is completely dry, cooled, and free of dust and grease (use a soft brush or compressed air to clean). Inspect the body for defects (cracks, pores), which must be repaired before glazing.

Glaze slurry preparation: Accurately measure the glaze materials and water according to the formula, mix thoroughly (preferably sieve) to the desired consistency, and let it settle to remove bubbles. Stir again before use.

Tool preparation: Prepare clean, appropriate brushes (different models may be needed for different areas), containers for holding the glaze slurry, stirring rods, clean water (for washing brushes), and racks for holding unglazed and glazed greenware (to prevent contact between pieces).

Operator preparation: The operator’s hands must be clean and dry. Understand the characteristics of the glaze slurry (such as drying speed) and the desired effect.

4.2. Post-glazing preparation:

Handle with care: Glazed pieces are extremely fragile (the glaze layer has not yet been fired), so they must be handled and placed with extreme care to avoid any bumps or fingerprints/scratches on the glaze surface.

Thorough drying: Place the glazed mugs in a well-ventilated, dust-free, safe (no people walking around and touching them) place to dry thoroughly and naturally. The drying time depends on the humidity of the environment and the thickness of the glaze layer. Make absolutely sure that they are completely dry before putting them in the kiln! Residual moisture will turn into steam when the kiln is heated, causing the glaze surface to crack and even the body to explode.

Final inspection: After drying, carefully inspect the glaze surface again for cracks, peeling, dust impurities, missed areas, or excessive buildup. Minor defects can be attempted to be repaired by gently sanding with extremely fine sandpaper (e.g., 800 grit or higher), but large-scale issues may require washing off and reapplying the glaze.

The glazing process is a test of the technician's experience. The quality of the glaze is usually determined by high-quality glaze materials, fine techniques, and strict management. With more than 20 years of professional ceramic mug production experience, China Ceramic Mug Factory has many experienced glazing technicians. We adhere to the concept of “details are fundamental, quality is life” to provide customized ceramic mugs for our customers.

Detailed explanation of the glaze spraying process for ceramic mugs

Xinxiang ceramic mug manufacturer, spray glazing is a surface treatment technique used in the production of ceramic mugs. A spray gun is used to atomize the glaze into tiny particles, which are then evenly sprayed onto the surface of the ceramic blank. Glaze is a glass-like coating that, when fired, gives ceramics smooth, waterproof, and wear-resistant properties, while also serving a decorative purpose. Spray glazing is suitable for complex shapes (such as unconventional mugs) or ceramic mugs that require fine gradation effects. Compared with traditional dip glazing, it allows for more flexible control of glaze thickness and coverage.

1. Spray glazing operation process

The spray glazing process is more advanced than dip glazing. Currently, ceramic mug factories commonly use two types of spray glazing processes: manual spray glazing and automatic spray glazing. Manual spraying requires a spray gun and air pump. The technician holds the spray gun, keeping it 20-30 cm away from the mug, with an air pressure of 0.3-0.5 MPA, and moves the spray gun at a constant speed, first covering the edges and recesses, then spraying the entire surface to ensure an even glaze layer. Complex areas (such as the inside of the mug handle) need to be sprayed repeatedly. Automatic assembly line operation: Place the ceramic mug blank upside down on the rack and send it to the conveyor belt. When the rack moves the ceramic mug under the spray gun, it rotates at a constant speed for 2-5 seconds (the dwell time is determined according to the different glaze materials and requirements) to spray the glaze. After spraying the glaze, check the ceramic mug blanks. If there are any areas missing glaze, use a brush or sponge to fill in the glaze. Finally, clean up the excess glaze at the bottom of the blanks to prevent them from sticking to the kiln plate during firing.

2. The difference between spray glazing and dip glazing

Operating method: Glaze spraying relies on equipment for application, while glaze dipping involves directly immersing the green body into glaze slurry to absorb it. In automated production lines, the cost of glaze spraying and glaze dipping lines differs.

Applicable scenarios: Spraying glaze is suitable for complex shapes or partial glazing (such as mugs with transitional colors); dipping glaze is suitable for simple shapes and ceramic mugs with low glaze color requirements. Dipping glaze is highly efficient but not as good as spraying glaze in terms of detail.

Glaze layer effect: Spray glazing can control the thickness of the glaze layer to achieve gradations or textures; dipping glazing produces an even glaze layer but tends to accumulate glaze on the edges.

Cost and difficulty: Spray glazing requires equipment investment and high operating skills; dipping glazing is low in cost and suitable for the production of conventional ceramic mugs.

3. Precautions fspray glazing

or The spray glazing process uses a spray gun to apply glaze to ceramic mugs. The glaze slurry has strict requirements. If it is too thick, it will clog the spray gun, and if it is too thin, it will not provide sufficient coverage. In addition, the glaze slurry needs to be stirred regularly to prevent sedimentation. The spray gun needs to be thoroughly cleaned after each use to prevent residual glaze from clogging the spray gun and to prevent residual glaze from being sprayed onto the greenware after drying, causing debris to fall on the ceramic mug. During the glaze spraying process, avoid spraying at a fixed point for a long time (which can easily cause glaze flow). The key is to coordinate the movement speed of the rack with the air pressure of the air gun. Additionally, workers in the spraying workshop must wear masks and goggles to avoid inhaling glaze dust.

4. Preparation before spraying glaze

Body treatment: After drying, the ceramic mug body must be completely cooled, and surface dust must be removed with compressed air.

Glaze Preparation: Adjust the glaze slurry. For specific instructions, please refer to “Instructions for Making Glaze in Ceramic Mugs”

Test spraying: Test spray on scrap clay or bisque-fired pieces to observe glaze adhesion. Adjust the rotation speed and time of the stand, as well as the air pressure of the spray gun.

5. Post-glazing treatment

After spraying the glaze, the raw ceramic mug needs to be dried. During the drying stage, the raw mug should be kept out of direct sunlight or strong winds, and it is best to dry it naturally in the shade for 6-12 hours (depending on the humidity). After applying the glaze, the glazed surface needs to be inspected, mainly to observe whether the glaze is uniform under strong light, with a focus on checking areas prone to leakage, such as the handle connection and the rim of the mug. In addition to inspection, the glaze on the bottom of the mug should be removed so that the part of the ceramic mug that comes into contact with the kiln plate remains free of glaze. Finally, the ceramic mug blanks are placed on the kiln plate with spacing between them and wait to be fired in the kiln.

6. Six major defects that are likely to occur

6.1. Uneven glaze surface

Some substandard colored glazed ceramic mugs have uneven glaze thickness on the surface, which can be distinguished by the naked eye. The orange peel glaze phenomenon of ceramic mugs that we discussed earlier is a relatively obvious example. For the specific causes of this issue, please refer to “Research and Solutions for the Orange Peel Glaze Phenomenon in Ceramic Mugs”  .

6.2. Glaze cracking

After the ceramic mug is glazed and dried, cracks appear. These cracks are mainly divided into horizontal, vertical, and mesh patterns. The main reasons for this are: a. The glaze layer is too thick (>0.5mm) or the glaze has been sprayed multiple times. Because the glaze layer is too thick, cracks are likely to appear on the glaze surface during the drying stage of the ceramic mug. b. The ceramic mug dries too quickly during the glazing and drying stage. The main reasons for this are that the temperature in the drying workshop is too high or there is a strong wind blowing directly on it.

6.3.  Grainy glaze surface

There are obvious bumps on the glaze surface of the ceramic mug. The main reason for this phenomenon is the glaze. The glaze is too coarse, and the particles in the glaze slurry are sprayed onto the ceramic mug. Another reason is that the spray gun is not cleaned regularly, causing the previous glaze to clump together and be sprayed onto the ceramic mug.

6.4. Glaze flow

This phenomenon is similar to the first type of uneven glaze surface. Glaze flow mainly occurs at the bottom and rim of the mug. If we disregard the glaze itself and only consider the glazing process, then local glazing will lead to glaze flow.

6.5. Pinholes/bubbles

Pinhole and bubble defects in ceramic mugs during the glazing process are mainly caused by bubbles and impurities in the glaze, or dust on the greenware.

6.6. Glaze peeling

If the glaze peels off a spray-glazed ceramic mug, there are two possible causes. There are two reasons for this: one is that the green body is contaminated with oil or dust; the other is that the moisture content of the green body is too low. This prevents the glaze from adhering properly to the green body, causing the glaze layer to peel off.

Spray glazing is a process that is often used when customizing ceramic mugs. This process has obvious advantages when dealing with mugs of special shapes and mugs with special requirements for the glaze surface. The essence of good glaze spraying lies in the combination of “standardization” and “refinement.” From raw material selection and glaze preparation to the glazing process, every step is controlled by the people at Xinxiang Ceramics Factory. China Ceramics Mug Factory believes that only by converting process parameters into executable SOPs and continuously optimizing every detail can the best balance between efficiency and quality be found.

Ceramic mug dip glaze process details

Xin xiang custom ceramic mug manufactuer, in the previous section we talked about the phenomenon of orange peel glaze on ceramic mugs. One reason for this is the glazing process. Our common ceramic mugs are glazed, professionally this kind of mug is called color glaze mug. Many people said, we see the color glaze mug very little ah, are like: sublimation mug, printing mug, travel cup, stoneware mug, etc.. In fact, these ceramic mugs have a layer of glaze on the body, strictly speaking, they all belong to the color glaze mug. Only, on the basis of color glaze mugs, they have their own independent characteristics, so they are named after their characteristics. Well, let's talk about the glazing process of ceramic mugs, the glaze developed into a glaze paste, attached to the ceramic mug billet process, called glazing. Common glazing methods include dip glaze, spray glaze, brush glaze, pouring glaze and so on. Today we focus on a talk: dip glaze process.

1. Glaze before the preparation

Before the formal dip glaze, ceramic mug factory is to do some preparatory work. The purpose of these preparations is to ensure the success of the glazing process, reduce the rate of defective products. These preparations are mainly divided into 4 parts:

1.1. Clean ceramic mug raw blanks

In the previous article we will have, after the clay made of ceramic mug billet, to carry out the “Ceramic mug clay billet drying and billet repair process”  During the drying process, the blanks may be dusted. If the dust on the mug is not cleaned up, then the adhesion of the glaze is reduced and the ceramic mug we get in our hands is prone to problems. In this process, the raw blanks need to be cleaned with an air gun. At the same time, but also to detect the water content of the raw ceramic mug, the most suitable glaze water content is: 3% -5%. Raw billet water content is too low, it will be excessive water absorption, damage the structure of the glaze; water content is too high is prone to pinholes, flowing glaze and other problems.

1.2. Raw ceramic mugs

Whether the raw ceramic mugs should be plain fired, we have explained in the previous article. “What is plain firing of raw ceramic mugs?”.  Some ceramic mugs with complex shapes or special requirements for the thickness of the mug, need to be fired before glazing. Vegetable firing process, can enhance the quality of the ceramic mug billet, in the later glaze, hand-painted, paste underglaze flower paper and other processes, is essential, this link is not all ceramic cups, only for high-end ceramic cups.

1.3. Prepare glaze

Quartzite, feldspar, kaolin, after powdering, sieving, mixing slurry, etc., made of glaze paste, these specific operations in the “glaze raw materials, production, classification and quality” explained in detail. Before glazing, the glaze paste should be stirred and tested, mainly checking the color and fluidity of the glaze paste.

1.4. Cleaning the workshop

The glazing workshop in a ceramic factory is cleaned separately before formal glazing. It is the same as ceramic mug raw cleaning, in order to guarantee the cleanliness of the glaze on the ceramic mug. The main thing is to clean up the dust, control workshop temperature and humidity. Workshop temperature is generally controlled at about 25 ℃, humidity control at about 50%.

2. Ceramic mug dip glaze

2.1. Basic principle

Utilizing the water-absorbing properties of ceramic mug blanks, the surface is uniformly adhered to by immersing the glaze paste, similar to the principle of painting oil paintings. The glaze paste penetrates into the pores of the ceramic mug under capillary action, forming a 0.2-0.3mm thick glaze layer.

2.2 Scope of application

Dip glaze on the shape of the ceramic mug is required, regular cylindrical, conical ceramic mugs, using dip glaze. Dip glaze because the operation is simple, with automatic dip glaze equipment, for large orders, often used dip glaze process.

2.3 Operation steps

Mechanical arm grips the upper edge of the mouth of the mug at 1/3, the raw billet is vertically immersed in the glaze paste, keep the glaze surface 5mm away from the mouth of the mug, hold it for 2 seconds, and then lift it away from the glaze surface at an even speed. After lifting, the mechanical arm rotates 3-5 turns at 60 rpm to shake off the excess glaze. During this process, keep the mouth of the mug tilted downward by 15 degrees to discharge the accumulated glaze using gravity.

3. Drying and finishing

3.1 Drying

After glazing, place the raw ceramic mugs horizontally on the grid drying rack, and require the ambient temperature to be about 25℃ and humidity to be about 50%, drying for 2 hours. Then, raise the ambient temperature to 40℃, humidity 30%, and activate the circulating fan to accelerate the drying for 5 hours.

3.2. Finishing

Use sponge, scraper and other tools to clean up the mouth and bottom of the mug, excess glaze.

4. Quality Inspection

Grade A standard: glaze without pinholes, bubbles (diameter <0.2mm); thickness fluctuation <±0.05mm; mug roundness error <0.3mm.

5. Common Problems

5.1: Glaze accumulation at the mouth of the mug (“glaze circle”)

Causes: insufficient rotating speed of dumping glaze / too deep immersion glaze

Countermeasures: Increase the speed to 80 rpm; install limiters to control the depth of immersion.

5.2: Lack of glaze on the handle

Causes: Air bubbles attached / Mechanical arm clamping obscured

Countermeasures: ultrasonic vibration to remove bubbles before dipping glaze.

5.3: Glaze layer peeling off

Phenomenon: after drying the glaze appears spider web cracks

Root cause treatment: adjust the glaze paste formula (add thickener)

5.4: Uneven thickness

Means of detection: every 30 pieces with a thickness gauge sampling test

Process optimization: the specific gravity of glaze paste is stabilized at 1.45; add automatic replenishment pump to maintain a constant liquid level.

5.5: Glaze pollution

Pollution source tracking: 60% from workshop dust; 30% from impurities in the glaze tank.

6. Analysis of advantages and disadvantages of glaze dipping method

6.1 Core advantages

Outstanding efficiency: single machine handles 800-1200 pieces per hour

Low cost: the utilization rate of glaze material＞95%.

Stable quality: pass rate up to 92%-95%.

6.2 Inherent limitations

Weak adaptability: not suitable for relief/shaped mugs

Edge defects: the mouth of the mug needs to be processed twice.

The immersion glaze method is still the mainstream glazing process for ceramic mugs after centuries, and its essence lies in the combination of “standardization” and “refinement”. As the old craftsman said: “dip glaze three points by equipment, seven points in the management.” Even the most sophisticated equipment, but also need people to manage. The production of ceramic mugs is a process of detailing. From raw material selection, glaze preparation to glaze process, each link has Xinxiang ceramic factory people on the details of the control.  China ceramic mug factory believes that the only way to find the best balance between efficiency and quality is to transform the process parameters into enforceable SOPs and continuously optimize every detail.

Ceramic mug orange peel glaze phenomenon research and solution

Xin xiang custom ceramic mug manufacturer, many ceramic mug buyers get ordered mugs, its body is not smooth, (exceptions for special needs such as frosted mug, matte mug, etc.). Ceramic mugs like this, in fact, belong to the unqualified products. China ceramics factory stands in the producer's point of view, for ceramic mug surface appears similar to the unevenness of the orange peel phenomenon (commonly known as “orange peel glaze”), to explain the reasons for its formation. The main reasons include: glaze formula, firing process and billet quality.

1. what does orange peel glaze look like?

Imagine the skin of a fresh orange: covered with tiny bumps, uneven to the touch. Ceramic mug if the appearance of orange peel glaze, looks like the orange peel “printed” on the cup. Specific performance: surface roughness: the original should be smooth surface of the mug appeared wavy undulation; dull luster: like a layer of mist, reflective effect is poor; feel bad: finger scratching can obviously feel the grain. This defect not only affects the beauty of the ceramic mug, but also reduces the grade of the cup, and even lead to serious glaze flaking.

2. Why does orange peel glaze?

Ceramic mugs appear orange peel glaze phenomenon, very similar to our failure to do the cake. When making a cake, if the quality of the cream, flour problems, or baking temperature is not controlled, it is easy to make a failed cake. The orange peel glaze of ceramic mugs is also due to the glaze and firing process.

2.1. glaze viscosity

In the previous article about ceramic mug glaze (Instructions for making glaze in ceramic mugs), we introduced. Before a glaze is put into the kiln and fired, it is a paste-like liquid. When a mug is coated with glaze and fired in a kiln, it becomes a smooth “glass layer” on the surface of the mug. The role of kaolin in the glaze, play the role of the binder. The glaze paste adjusts the viscosity of the glaze by adjusting the content of kaolin and water. If the proportion of kaolin exceeds 15%, then its viscosity is too strong, and the phenomenon of orange peel glaze will easily appear. If the glaze is not finely ground enough, the diameter of the particles inside is too large. Then, such a ceramic mug will be covered with fine bumps, feel uneven, and have a poor luster.

2.2. Glaze too thick

Ceramic mug glazing process, we have talked about it before. It is mainly divided into: dip glaze, spray glaze and brush glaze. In the glazing process, whether the glaze is uniform, can lead to ceramic mug flow glaze. Similarly, whether the glaze thickness meets the requirements also determines whether the mug will appear orange peel glaze phenomenon. If the glaze is applied too thinly, especially with darker colors, you will notice that the mug will have a vaguely ceramic undertone. If the glaze is applied too thickly, exceeding the safe thickness of 0.25 mm, the ceramic mug will be prone to orange peel glaze.

2.3. Firing

The firing process is what transforms a mug from “clay” to “ceramic”. In the previous article, we introduced the firing process of various equipment, temperature and humidity control (In-depth analysis of the firing process of ceramic mugs) . So, how does the firing process lead to the orange peel glaze on ceramic mugs? Mainly because: in the heating stage, the heating speed is too fast or missing insulation stage, resulting in the glaze is not uniformly melted on the beginning of solidification; another reason is that the kiln does not reach the high temperature of the glaze melting (for example: the kiln is no longer warmed at 1250 ℃, resulting in the glaze is not completely melted); the last reason is that the kiln is too fast to cool down, high-temperature heat preservation time is not enough, resulting in the glaze suddenly shrinkage caused by the orange peel glaze phenomenon.

2.4 Failure of Raw Billet

In addition to the above 3 reasons, leading to the phenomenon of orange peel glaze, there is another kind of ceramic mug raw billet reason. Glaze, glaze, firing, these three processes are acting on the ceramic mug billet. Ceramic mug raw material if the iron content is higher than 1%, iron and glaze will produce exclusion reaction, the phenomenon of orange peel glaze. If there is dust on the surface of the ceramic mug raw billet, resulting in reduced glaze adhesion during the glazing process, will also produce the phenomenon of orange peel glaze.

3. How to solve the orange peel glaze

According to the practical experience of China ceramic factory, the following measures can reduce the incidence of orange peel glaze from 20% to 3%:

3.1 Improve the glaze formula

Add “lubricant” to the glaze - borax and lithium faience, used to stabilize the viscosity of the glaze. In the powdering stage of the glaze material, the precision and grinding time of the ball mill should be ensured, and in the sieving stage, the fineness of the glaze material should be ensured. In addition, the use of stable quality raw materials, pay special attention to the content of iron and sulfur.

3.2 Control glaze application

At present, China ceramic factory adopts automatic glazing assembly line to make the glazing process and quality inspection more rigorous. Through the automated assembly line, the glazing process is guaranteed to be uniform, and the glaze thickness error is within 0.01mm. Through this, the glazing process of ceramic mugs is guaranteed to be problem-free.

3.3. Kiln automation

China's previous kilns were mostly based on traditional kilns, and the firing process was mainly dependent on the experience of the technicians. Nowadays, kilns use automation from fuel to temperature control. The heating up time, firing temperature, holding time and cooling down process are precisely controlled by computer.

3.4. Clean Raw Billets

The ceramic factory itself is with the concentration of clay and ceramics, so the production plant is relatively dusty. Ceramic mugs need to be dehumidified and dried after the production of raw blanks (Drying and trimming process of ceramic mug clay blanks). Raw billet in the drying stage, it is inevitable to fall on the dust, in the later part of the glaze link will be prone to problems. Ceramic factory for this problem using measures are mainly, control the environment of the drying plant; glaze before the use of air guns to clean the billet.

4. Frequently Asked Questions

Q1：Home to buy a mug with orange peel glaze, can I still use it?

A: Mild orange peel glaze does not affect the use, but heavy may lead to glaze off, it is recommended to replace.

Q2：How to judge the orange peel glaze with naked eyes?

A：Rotate the mug to the light, the smooth glaze will reflect evenly, and the orange peel glaze will have bright and dark ripples.

Q3：Why do some handmade mugs intentionally do orange peel effect?

A: The deliberately created texture is different from the defects, which are usually evenly distributed and treated with anti-peeling.

By understanding the glaze characteristics and controlling the production process, orange peel glaze can be completely avoided. This is not only a technical problem, but also a test of craftsmanship - China Ceramics Factory strives for excellence in every link in order to guarantee that every mug is smooth as a mirror and warm to the heart.

Defects in customized ceramic mugs - pinholes

Xin xiang custom ceramic mug manufacturer, pinhole is a ceramic glaze on the emergence of tiny holes (diameter usually 0.1-1mm), pinhole is the essence of the firing process gas can not be discharged from the glaze layer in a timely manner due to the specific causes can be traced back to the 5 major links.

1. What is a ceramic mug pinhole

Pinhole is a ceramic glaze on the emergence of tiny holes (diameter usually 0.1-1mm), shaped like a needle prick marks, when the seriousness of the dense honeycomb. According to the stage of occurrence can be divided into two categories: open air holes: through the glaze layer directly to the billet, the cross-section was funnel-shaped, easy to hide dirt; closed air holes: the glaze layer is not penetrated, the surface only left pits, affecting the appearance of gloss. Pinhole, as in the baking of cakes, the internal air bubbles are not discharged, the surface of the formation of collapsed pits.

2. pinhole is the essence of the firing process gas can not be discharged from the glaze layer in a timely manner due to the specific causes can be traced back to the 5 major links:

2.1. Raw material impurities generated by the gas

Pyrite (FeS₂) in the blank or humus in the clay, decompose at 300-800 ℃ to release SO₂, CO₂ gas. The use of cheap kaolin with sulfur content > 0.1%, the pinhole rate after firing surges to more than 20%.

2.2. Defects in glaze preparation

When the grinding fineness of the glaze is not enough, the glaze particles>30μm, the gas channel is formed in the gap between the particles, resulting in the glaze containing gas. Glaze paste contains air bubbles: excessive mixing introduces air, no defoamer (such as n-butanol) is added, and air holes are left after the glaze layer is dried. The glaze should be sieved through a 400 mesh sieve (pore size 38μm) during the screening stage to reduce pinholes by 60%. Glaze paste in the mixing process to add defoamer, not stirred too much, and storage should also refer to the previously described standards for storage.

2.3 Firing too quickly

Ceramic mug billet firing in the kiln, water evaporation period (room temperature ~ 300 ℃), if the rate of heating > 150 ℃ / h, then the ceramic mug billet inside the steam will break through the glaze layer to form pinholes. In the decomposition and oxidation period (300-900 ℃), the rate of heating > 200 ℃ / h, sulfur or carbide will decompose gas, the formation of pinholes.

2.4 Lack of heat preservation

If a 30-minute holding section is not set up for the raw ceramic mug during the firing heating phase, specifically before 900°C, gases will remain in the glaze and form pinholes.

2.5. Excessive air pressure in the kiln

Inside the kiln, when the exhaust fan power is insufficient, resulting in air pressure in the kiln > 10Pa, it will prevent the escape of gas, resulting in the ceramic mug gas can not be discharged normally, forming pinholes.

3. The formation of pinholes is mainly due to the above five reasons. So, how can ceramic mug factory improve in order to reduce the chances of pinholes in ceramic mugs?

3.1. raw material pretreatment

Since the sulfur in the clay raw materials can lead to the emergence of pinholes, then in the raw material preparation stage, we need to target the reduction of sulfur content in the clay, to control it within 0.1%. Specific methods include, washing and flotation of kaolin (removal of sulfides), or adding 1% barium carbonate (BaCO₃) high-temperature sulfur fixation; billet sealed aging for more than 15 days to promote the decomposition of organic matter, reducing the amount of fired gas production.

3.2. Glaze optimization

The grinding degree of the glaze is not enough particle gap is too large, it will be easy to make the air mixed into it, resulting in pinholes. Then, we have to glaze raw materials in the screening stage over 400 mesh sieve to reduce large particles. In the raw material grinding stage, the ball mill is used to grind to the 10,000-hole sieve residue <0.05%. In addition, add 0.5% magnesium oxide (MgO) to expand the melting range of the glaze and extend the gas discharge time. In the glaze slurry storage stage, 5% zirconium silicate (ZrSiO₄) can be added to improve the glaze high-temperature viscosity and close the external gas.

3.3. Firing temperature control

There are several temperature nodes mentioned above in the process of raising the raw billet from room temperature to 900°C. One is room temperature-300℃, to control the speed of heating, in the season that is not winter, to control the heating time should not be less than 2 hours. In 300-900 ℃, to control the time should not be less than 3 hours. In addition, every 100 ℃, to set aside 5 minutes of insulation period. Used to allow the ceramic mug billet in the body of the organic matter or sulfide, can be fully decomposed, and there is enough time for gas discharge. 900-1250 ℃, need 4 hours. Holding is also necessary during the vitrification stage of the glaze.

3.4. Control of kiln air pressure

The kiln needs to have an oxidizing flame and a reducing flame during firing. When ceramic mugs are fired, their content varies somewhat depending on the stage. The overall principle is to be a temperature section of a temperature section of the firing, in the firing of air pressure should be controlled at negative pressure -5 ~ 0Pa, the most appropriate. Can make the fired ceramic mug more stable, less pinhole defects.

In summary, the formation of pinholes in ceramic mugs, the root cause is that the gas is not discharged from the raw billet. The formation of pinholes is twofold, one is the raw materials, including clay and glaze raw materials, and the second is improper control of the firing process. Pinholes in ceramic mugs can not be avoided, China Ceramic Mug Factory, through strict control of the quality of raw materials and improve the precision of firing control, to minimize the chances of pinholes, to provide customers with high quality and stability of ceramic mugs.

In-depth analysis of the firing process of ceramic mugs

Xinxiang custom 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.

3 production methods and 2 decal methods for ceramic mug decals

Xinxiang custom ceramic mug manufactuer, the process of making ceramic mugs, the clay will become ceramic mugs raw blanks after some series of processes. Ceramic mugs of raw blanks need to be embellished, in the previous article, we introduced the glaze knowledge of ceramic mugs, this article, we talk about ceramic cups of flower paper. In the previous China ceramics introduced ceramic flower paper category is suitable for microwave oven, also introduced, water decal process. Today, we systematically and comprehensively introduce the knowledge of ceramic mugs paper.

1. What is flower paper

Ceramic cup flower paper, is a ceramic mug “makeup” means. It is like a kind of tattoo stickers, through the firing process, the customer's customized pattern, fused to the ceramic mug. Let different ceramic mugs have different pictures, suitable for different people and scenes. So, how is the ceramic flower paper made up? It has 3 layers. The lowest layer is the base layer that holds the pattern. The most commonly used materials for the base layer are kraft paper or water-soluble paper. The base layer is discarded after the application and cannot be involved in the firing. The second layer is the pattern layer, which is made up of pigments. The patterns and colors we choose are reflected in this layer. There are three processes for producing this layer: lithography, screen printing and digital printing. The pattern layer is produced through one of these processes. The top layer is the cover oil layer. The function of this layer is to protect the pattern layer in the center.

2. Flower paper classification

According to the material of the flower paper can be divided into 3 categories: acetal film paper, underglaze flower paper and water transfer decal paper. Often seen is the water transfer paper, today mainly to explain this one. The other two, we will talk about later. According to the firing temperature, ceramic mugs can be divided into: high-temperature paper and low-temperature paper. Purchasers are often asked by the ceramic mug factory is: “this ceramic mug needs high temperature paper or low temperature paper”. According to the temperature distinction between paper, is the most important thing for buyers to understand.

2.1. High-temperature paper firing temperature is 780-850 ℃, high-temperature paper color is light, high solidity. Low temperature floral paper firing temperature is 650-750 ℃, its color is very bright, very bright red and gold are low temperature floral paper. So, what causes them to have different firing temperatures and different vibrant colors after firing? Actually, it's similar to the glazes in our last post. The colors all come from metal oxides. The metal oxides cobalt, manganese, etc. that are used for the colors in the high-temperature flower paper have a high melting point, so they are high-temperature flower paper. On the contrary, low-temperature flower paper with cadmium, selenium and other metal oxides, these oxides are less resistant to high temperatures, but the color is bright, and the firmness of the firing is not as good as high-temperature flower paper.

2.2. High-temperature flower paper and low-temperature flower paper need different adhesives. High-temperature flower paper glue: the glue is natural resin (such as rosin) or high-temperature glue, when fired will be completely burned to ash, leaving no residue. This way the glaze is smooth and will not blister. If the glue is not burned clean, the glaze will have black spots (like burnt rice grains). Glue for low-temperature floral paper: organic resins (such as acrylics) are used, and they burn clean at low temperatures. However, if the temperature is not high enough, the glue residue will stick to the glaze and be sticky to the touch. After firing at low temperature, if you wipe the mug with a wet cloth, the glue residue may whiten (like a tape mark).

3. Flower paper production process

3.1. Lithographic printing (offset printing)

Lithography is the production of patterns on aluminum printing plates, each color corresponds to a plate. When printing, the ink adheres to the raised portion of the printing plate and is transferred to the patterned paper by means of a rubber cylinder. This technique is suitable for mass production and has the lowest cost, which is about $0.1 to $0.3 per sheet of floral paper. If the order quantity exceeds 100,000 pieces, lithography is the most economical choice. However, its disadvantage is that the color is not bright enough, can only print a maximum of 6 colors, and can not show metallic or three-dimensional effect.

3.2. Screen Printing (Screen Printing)

Screen printing needs to make a separate screen plate for each color, through manual color printing layer by layer scraping. For example, when making a gift mug with a gold embossed pattern, workers need to repeatedly scrape 3 to 4 times to increase the thickness of the ink layer. The advantage of this technique is that it can achieve three-dimensional effects (ink layer thickness of up to 0.1 to 0.3 mm) and metallic colors, and is suitable for medium-volume orders (5,000 to 50,000 pieces). However, the color register error is large (about ± 0.5 mm), small characters or fine patterns are easy to blur, and each color needs to be dried, the production cycle is long.

3.3 Digital printing (inkjet printing)

Digital printing eliminates the need for plate making and directly prints the pattern onto the floral paper with ceramic ink, which is cured by ultraviolet light. Digital printing can be done quickly and in rich colors, supporting photo-quality gradient effects. It has the highest flexibility, with orders starting at 50 sheets, but it also has the highest cost ($5 to $8 per sheet) and special colors such as gold need to be filled in later by hand.

3.4. Core differences between the three technologies:

Cost: lithographic < screen < digital (suitable for orders from large to small).

Color effect: digital ＞ screen ＞ lithographic (from gradient to metallic).

Production speed: lithographic suitable for long-term large quantities, digital suitable for urgent small quantities.

4. Decal operation steps

4.1 The first step: pretreatment

Clean the mug: use non-woven cloth dipped in 95% alcohol to wipe the glaze surface to ensure that there is no dust, oil or water marks. If you use paper towels may be residual fluff, wipe with water will lead to poor decal.

Preheat the mugs: leave them in the preheating zone at 40-50°C for 3-5 minutes, especially in winter, to avoid condensation when appliqueing cold mugs which may cause the pattern to shift.

4.2. Step 2: Applique operation

4.2.1. Soaking method (flat mugs):

a. Soak the decal paper in 25℃ water for 8-12 seconds to separate the backing paper from the pattern layer.

b. Slide the pattern onto the surface of the mug, fix the center first, and then use the rubber scraper to scrape from the center to the edge at an angle of 45° to discharge the air bubbles. If the scraping force is too strong, the pattern may be torn, and the residual air bubbles will produce pinholes after firing.

4.2.2. Transfer film method (curved mugs)

a. Cover the pattern paper with transfer film and compact it to make sure there are no air bubbles.

b. Slowly tear off the backing paper and stick the film with pattern to the mug surface, use 60℃ hot air gun to locally heat to assist bonding.

c. Tear off the transfer film evenly, too fast may result in pattern residue.

4.3. Step 3: Drying and Quality Inspection

4.3.1. drying: dry at 55-60 ℃ for 15-20 minutes, touch no wet feeling can be. Too high temperature will lead to glue failure.

4.3.2. QC:

Alignment accuracy: check the pattern splicing at the mug handle, mug mouth, etc., the error needs to be less than 1mm.

Edge checking: use strong light to observe whether the edge is warped or not, and the decal glue needs to be reapplied after discovery.

Bubble treatment: use the tip of a needle to poke bubbles and make up the glue, otherwise it will burst when firing.

4.4 Step 4: treatment before entering the kiln

a. Dust removal: blow the surface of the mugs with an ionic air gun, especially at the inner edge of the mouth of the mugs where dust is likely to accumulate.

b. Stacking protection: invert the mugs on the silicone shelf to avoid handling the pattern.

5. Precautions for the decal process

a. Environmental control: decal workshop needs to be maintained at about 25 ℃, humidity 60%, to avoid deformation of the paper or glue failure.

b. Flower paper preservation: avoid light and flat, expired flower paper (more than 1 year) glue will fail, easy to fall off after sticking.

c. Burning risk: low-temperature flower paper (such as gold) need to strictly control the temperature, more than 750 ℃ may lead to metallic color blackening. The heating stage (300-600℃) needs to be slow (3℃ per minute) to prevent the pattern from cracking.

d. Pattern haloing: Applique when the glaze is not thoroughly dry, need to ensure that the glaze is dry for more than 24 hours after application.

e. Lack of color after firing: check the ink thickness (screen printing needs to be ≥ 20 microns) or kiln temperature is too high.

f. Blackening of the gold edge: the gold-containing flower paper should be fired in the oxidizing flame to avoid contact with smoke.

g. Decals off: Decals need to be put into the kiln within 8 hours, otherwise the glue fails.

Different images of ceramic coffee mugs are derived from ceramic flower paper. The cost and difficulty of making ceramic flower paper is determined by the number of colors, whether there are gradient colors, and special colors such as red, gold and silver. The raw ceramic is the foundation of the mug, and the quality of the glaze and the paper is a direct factor in the aesthetics of the mug. The above information is based on the quality of ceramic flower paper hardware guarantee, ceramic mug flower paper is beautiful, but also by virtue of the ceramic mug factory technical workers operating practices and quality control guarantee. Both hard and soft to ensure that we get our hands on a beautiful ceramic coffee mug.