The Cracking Conundrum: Understanding Crazing in Ceramics

Crazing in ceramics is a network of fine cracks that can appear on the glazed surface of pottery. This phenomenon occurs due to differences in the thermal expansion rates between the glaze and the clay body. Crazing can affect the durability of ceramics and may be intentional or unintentional.

Beyond the Surface: The Science and Art of Crazing in Ceramics

Crazing is a common phenomenon that occurs in ceramics when there is a difference in the rate of contraction between the glaze and the body of the piece. This results in a network of fine cracks on the surface of the glaze, which can be visible or only felt when touched. I have found that crazing can occur in any type of ceramic piece, from functional to decorative. While it can be aesthetically pleasing and add character to a piece, it can also weaken the structural integrity of the object and make it susceptible to staining or other forms of damage. Therefore, it’s important to understand crazing and how to prevent it.

“Crazing is a common phenomenon in ceramics that occurs when the glaze on the surface of the clay body contracts more than the clay body itself.”

Ed Shears

Why does crazing occur in ceramics?

Crazing in ceramics occurs due to a mismatch in the coefficient of thermal expansion between the glaze and the clay body during the cooling process. As the pottery cools, the glaze contracts more than the clay, leading to small cracks in the glaze called crazing. The degree of crazing can vary depending on the type of clay, glaze, and firing temperature used. Other factors, such as the age of the piece and exposure to moisture, can also contribute to crazing over time. Proper control of the firing process and the selection of compatible clay and glaze materials can help prevent or minimize crazing.

What are the different types of crazing in ceramics?

Crazing in ceramics can be classified into several types based on the appearance of the cracks. One type of crazing is called “mesh crazing,” which is characterized by a network of tiny cracks that resemble a mesh or net. Another type is “pattern crazing,” which produces a distinct pattern of cracks that can be seen on the surface of the glazed ceramic. “Spiderweb crazing” is another type that creates a radial pattern of cracks that look like a spider web. “Fine crazing” is a type of crazing that produces very small cracks that are barely visible to the naked eye. Finally, there is “catastrophic crazing,” which occurs when the cracks in the glaze are large and deep, leading to the formation of pieces of ceramic falling off.

“The presence of crazing in ceramics can affect both the aesthetic appearance and the functionality of the piece.”


Is crazing in ceramics always bad?

As an expert in ceramics, I would say that crazing is not necessarily always bad, as it can be intentionally created for aesthetic purposes. In fact, crazing is often desirable in certain types of pottery, such as traditional Japanese crackle glaze, which is prized for its unique and organic appearance. However, if the crazing is unintended, it can weaken the structure of the ceramic and make it more susceptible to damage or staining. It can also make it difficult to clean and maintain. Therefore, it ultimately depends on the intended use and aesthetic of the ceramic piece.

“Crazing is caused by a variety of factors, including the chemical composition of the clay body, the glaze, the firing process, and environmental conditions.”


How does crazing affect the value of ceramics?

As an artist with many years in ceramics, I can say that crazing can have a significant impact on the value of ceramic pieces. In some cases, crazing is desirable and can actually increase the value of a piece, particularly in certain types of pottery such as majolica or Raku. However, in most cases, crazing is considered a flaw and can significantly decrease the value of a ceramic piece, particularly if the crazing is severe or extensive. It is important for collectors and buyers to carefully examine the piece for crazing and to consider its impact on the overall value before making a purchase. As a ceramic artist or collector, it is also important to take proper care of ceramic pieces to prevent or minimize crazing, as it can be difficult to repair and may further reduce the value of the piece.

What factors cause crazing in ceramics?

Crazing in ceramics can be caused by various factors such as the coefficient of thermal expansion, clay body composition, and glaze fit. The coefficient of thermal expansion refers to the rate at which an object expands or contracts with temperature changes. If the glaze and clay have different coefficients of thermal expansion, the glaze can develop cracks or fissures as the piece cools. Clay body composition can also affect crazing, with certain clay types being more prone to it than others. Glaze fit, or how well the glaze adheres to the clay body, can also cause crazing if it is too tight or too loose. Other factors such as firing temperature, atmosphere, and cooling rate can also impact crazing in ceramics.

How does the glaze affect crazing in ceramics?

The glaze is one of the primary factors that affect crazing in ceramics. The coefficient of thermal expansion (CTE) of the glaze must match the CTE of the ceramic body for the glaze to fit properly without crazing. If the CTE of the glaze is lower than that of the ceramic body, it will cause the glaze to contract more than the body during cooling, resulting in tensile stress and crazing. Conversely, if the CTE of the glaze is higher than that of the body, the glaze will expand more than the body during cooling, resulting in compressive stress and potentially causing the glaze to crack. The fit between the glaze and the body is crucial in minimizing the risk of crazing.

How does the body of the ceramic affect crazing?

When it comes to crazing in ceramics, the body of the ceramic can play a significant role. The porosity and shrinkage rate of the ceramic body can impact the development of crazing in the glaze layer. If the body of the ceramic is too porous or has a high rate of shrinkage, it can cause stress in the glaze layer, leading to the formation of crazing. Additionally, the coefficient of thermal expansion (CTE) of the ceramic body can also impact the development of crazing. If the CTE of the body and glaze are not compatible, it can lead to stress and cracking, ultimately resulting in crazing. It’s important for ceramic artists and manufacturers to consider the characteristics of the ceramic body when choosing glazes and firing temperatures to minimize the risk of crazing.

Can firing temperature affect crazing in ceramics?

My experience says, yes, firing temperature can affect crazing in ceramics. Generally, the higher the firing temperature, the less likely it is for crazing to occur. This is because higher firing temperatures allow for the glaze and body of the ceramic to mature together more completely, reducing the amount of tension between the two layers. However, it’s important to note that firing temperature is not the only factor that affects crazing, and that other factors such as the composition of the clay body and glaze can also play a role.

How can humidity and temperature affect crazing in ceramics?

Humidity and temperature can affect the expansion and contraction of the ceramic body and glaze, which can lead to crazing. When ceramics are exposed to high humidity, the clay body and glaze can absorb moisture and expand, while low humidity can cause them to contract. These changes in size can create stress on the ceramic, leading to crazing. Similarly, rapid changes in temperature can cause the ceramics to expand or contract too quickly, which can also lead to crazing. Therefore, it is important to store ceramics in stable and controlled environments to prevent crazing.

How can you prevent crazing in ceramics?

I can suggest some ways to prevent crazing in ceramics. First, choose a glaze that has a similar coefficient of expansion to the clay body. Second, ensure that the glaze is applied evenly and thinly to the clay surface. Third, consider altering the firing temperature or cooling rate to reduce thermal shock. Fourth, avoid sudden changes in temperature or humidity during storage or display. Fifth, allow pieces to dry slowly and evenly to avoid trapped moisture. Finally, be aware of the clay and glaze materials used and their compatibility. By following these steps, you can reduce the likelihood of crazing and improve the overall quality and durability of your ceramics.

Can you fix crazing in ceramics?

Crazing in ceramics is a permanent issue and cannot be fully repaired. However, there are some methods that can help to reduce its visibility. One approach is to apply a thin coat of clear lacquer or wax over the entire surface to mask the lines of the crazing. Another method is to fill the cracks with paint, dye, or pigment to make them less noticeable. However, it is important to note that these methods are temporary solutions and may not completely hide the crazing. The best approach is to prevent crazing in the first place by controlling the factors that cause it, such as the glaze fit, the firing temperature, and the clay body.

Can you refire a crazed piece of ceramics?

Refiring a crazed piece of ceramics can potentially fix the crazing, but it is not always successful. Refiring at a higher temperature can help to melt the glaze and fill in the cracks, but it can also cause other problems such as warping, bubbling, or even cracking. It is important to carefully evaluate the piece and consider the risks before attempting to refire. It is also worth noting that refiring a piece can change its appearance, so it may not look exactly the same as before. In general, it is best to avoid crazing in the first place by properly controlling the firing process and using appropriate glazes and clay bodies.

How can you stabilize a crazed piece of ceramics?

It is possible to stabilize a crazed piece of ceramics, but the success rate depends on the severity of the crazing and the condition of the piece. One method involves applying a consolidant, which is a liquid material that fills the cracks and strengthens the ceramic. Another method is to use a humidification chamber, which slowly introduces moisture to the ceramic to encourage the cracks to close. However, it is important to note that these methods may not completely eliminate the appearance of crazing and may not be appropriate for valuable or historically significant pieces. It is always recommended to consult a professional conservator before attempting any repairs or stabilization methods.

Does crazing occur in all types of ceramics?

My experience has shown crazing can occur in all types of ceramics, whether it be earthenware, stoneware, or porcelain. It is a natural occurrence that can happen during the cooling process after firing, and is not specific to any type of ceramic body. However, certain types of glazes and firing temperatures can increase the likelihood of crazing. It is important for ceramic artists to be aware of this and take steps to minimize the occurrence of crazing in their work.

Does crazing occur more often in certain types of ceramics?

My experience has shown crazing can occur more often in certain types of ceramics. For example, earthenware and some types of stoneware are more prone to crazing compared to porcelain. This is because earthenware and stoneware have a more porous body compared to porcelain, which makes them more susceptible to water absorption and changes in temperature and humidity. However, crazing can occur in any type of ceramic, and it ultimately depends on factors such as the composition of the body and glaze, firing temperature, and environmental conditions.

How does crazing affect porcelain versus stoneware?

According to Meesh, artist, author, and product manager, “Crazing can occur in both porcelain and stoneware ceramics.” However, porcelain is more prone to crazing due to its lower coefficient of thermal expansion. This means that the glaze and body of the porcelain expand and contract at different rates during firing and cooling, which can cause stress and lead to crazing. Stoneware, on the other hand, has a higher coefficient of thermal expansion, making it more forgiving and less likely to experience crazing. Nonetheless, crazing can still occur in stoneware if the glaze and body have significant differences in thermal expansion coefficients.

How does crazing affect earthenware versus porcelain?

Crazing affects earthenware and porcelain differently. Earthenware is more prone to crazing due to its higher porosity, which means that it can absorb moisture more easily. Porcelain, on the other hand, is less prone to crazing due to its lower porosity. However, if the glaze and body are not properly matched in their coefficients of thermal expansion, crazing can still occur in porcelain. Crazing can be more visible and prominent in earthenware due to the higher contrast between the body and glaze.

How do you clean and care for crazed ceramics?

I advise, when it comes to cleaning and caring for crazed ceramics, it’s important to handle them gently. Avoid using abrasive materials or harsh chemicals, as they can cause further damage to the already fragile glaze. Instead, use a soft cloth or sponge with warm water to clean the surface of the piece. If necessary, a mild dish soap can be added to the water.

“Proper care and maintenance of crazed ceramics involves gentle cleaning and avoiding extreme temperatures and humidity.”

David Jackson

It’s also important to avoid exposing crazed ceramics to extreme temperatures or rapid temperature changes, as this can cause further cracking or damage to the glaze. Store the piece in a dry, stable environment away from direct sunlight or sources of heat.

If the piece is particularly valuable or fragile, it may be best to consult with a professional conservator or restoration expert for cleaning and care advice.

Can you use crazed ceramics for food and drink?

I do not recommend crazed ceramics be used for food and drink. Crazing provides a porous surface that can harbor bacteria, making it difficult to clean. Food and drink may seep into the cracks and can cause stains, discoloration, and odors. Additionally, crazed ceramics may be more prone to chipping and breaking. It is important to inspect the piece thoroughly before use and discard it if there are any signs of damage or cracks that penetrate the entire piece. If using crazed ceramics for display purposes only, it is recommended to avoid placing food or liquid in them altogether.

“Crazed ceramics should not be used for food or drink as the cracks in the glaze can harbor bacteria.”

Ed Shears

Can you display crazed ceramics?

Yes, you can still display crazed ceramics as they can still be visually appealing and unique. Some collectors even prefer the look of crazed ceramics as they see it as adding character to the piece. However, it’s important to note that if the crazing is severe and affects the structural integrity of the ceramic, it may not be safe to display as it could break or shatter. It’s always best to evaluate the level of crazing and determine if it’s suitable for display on a case-by-case basis.

Why does my ceramic mug have cracks in the glaze?

Ceramic mugs are a popular choice for many people, thanks to their durability, aesthetic appeal, and functionality. However, one issue that can arise with ceramic mugs is the development of cracks in the glaze, which can be unsightly and potentially compromise the structural integrity of the mug. These cracks are often the result of a phenomenon known as crazing, which is the development of fine cracks in the glaze surface of a ceramic piece.

There are a variety of factors that can contribute to crazing in ceramic mugs, including the composition of the clay body, the thickness of the glaze, and the temperature at which the mug was fired. Additionally, exposure to extreme changes in temperature or humidity can exacerbate existing crazing or even cause new cracks to form.

While crazing can be concerning, it is not necessarily a sign that the mug is unusable. However, if the cracks are deep enough to allow liquids to seep through the glaze and into the body of the mug, it may not be safe for food or drink use. In this case, it is best to retire the mug or repurpose it for decorative use only.

If you have a ceramic mug with cracks in the glaze, it is important to handle it with care to avoid further damage. Avoid exposing the mug to extreme temperatures or sudden changes in temperature, as this can cause the cracks to worsen or even lead to the mug shattering. Additionally, be careful when cleaning the mug, as harsh or abrasive cleaners can exacerbate existing cracks or cause new ones to form.

Conclusion And Summary

Crazing in ceramics refers to the occurrence of hairline cracks on the surface of a glazed ceramic object. It is caused by the difference in the coefficients of thermal expansion between the body and glaze of the ceramic, as well as other factors such as the firing temperature, humidity, and body composition. While crazing can negatively affect the appearance and value of a ceramic object, it is not always considered a flaw and can sometimes even enhance the aesthetic appeal.

Preventing crazing can be achieved through careful consideration of the glaze and body materials, firing temperatures, and environmental conditions during and after firing. While there are ways to stabilize or fix crazed ceramics, it is not always guaranteed to be successful. Despite the potential drawbacks of crazing, it is a common and interesting phenomenon in the world of ceramics that adds to the uniqueness and character of each piece.


As you already know, (you read this far) in the world of ceramics, the term ‘crazing’ refers to the phenomenon of the glaze developing a network of fine cracks over time, a characteristic that can be both admired and loathed by ceramic artists.

As you’re sitting at your pottery wheel, crafting a piece, you might not be considering the ware and glaze expansion, yet these play a significant role in the eventual appearance of your ceramic work. The interplay between these expansions and contractions during the firing cycle could lead to crazing.

Here’s the science behind it as I see it: as your ceramic piece cools down from the firing cycle, both the bisque pottery and the glaze contract. However, if the glaze contracts more than the clay body, it can lead to the formation of a web-like pattern of fine cracks. This is what we call crazing.

While some artists may view crazing as an imperfection, others consider it a beautiful, natural pattern, often intentionally induced in decorative pieces. The added texture and character can add a vintage or rustic charm to the piece, making it more appealing to some.

But beyond aesthetics, crazing could potentially pose issues. Delayed crazing, which occurs hours, days, or even weeks after the piece has been removed from the kiln, can be problematic. It can weaken the structural integrity of the piece and may even cause it to leak if it’s meant to hold liquids.

I say, crazing could also be problematic during the firing process itself. Crazed pieces can stick to the kiln shelf, damaging both the work and the kiln.

So, what can ceramic artists (you) do to prevent or limit crazing? Adding extra silica to the glaze is one common solution I know of. It enhances the glaze’s fit by increasing its thermal expansion, reducing the chance of crazing. Also, ensure that the glaze is appropriately matched to the clay body in terms of their expansion rates.

I recap by saying, crazing in ceramics is a complex issue that requires careful consideration. Whether you view it as a flaw or feature, understanding its causes and implications can greatly enhance your ceramic work. Remember, even the most uncrazed pieces bear the subtle fingerprints of the artist and the kiln’s fiery breath – marks of the beautiful chaos that is ceramics, right?


Ceramic Arts Network:

Lakeside Pottery:

Insight Live by Digitalfire:

Ceramic Materials Workshop:

The Complete Guide to High-Fire Glazes John Britt 2007
“With recipes for mixing, testing, applying, and firing hundreds of high-fire glazes, this fully illustrated reference will help all ceramists gain a better understanding of glazes and the factors that make them work.”

The Potter’s Dictionary of Materials and Techniques by Frank Hamer

The Ceramic Spectrum: A Simplified Approach to Glaze and Color Development by Robin Hopper

Glazes Cone 6: 1240 C / 2264 F by Michael Bailey

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