Understanding and Preventing Cracks in Porcelain and Other Clay Bodies

Working With Porcelain: Why It Isn’t Difficult—Just Different

Porcelain is often regarded as a challenging clay body to work with.  Potters who attempted it often like the medium, however some give up not understanding how to handle the medium. They perceive it as fragile, finicky, and tedious. However, my challenging personality and years of experience have led me to a different perspective. Today, I advocate for working with porcelain clay. While it is demanding,  the rewards and benefits make it all worthwhile. 

My Early Journey With Porcelain Clay
My first experiences working with porcelain, was unsuccessful. To make it worse, more experienced potters and instructors  intimidated me. In my early days of pottery I created simple forms, fired to cone 8.  
Much of my early porcelain work ended up in pit firings. I created incredibly thin porcelain pieces that were fired in pits. These works eventually helped me secure permanent residency for my family and me in the United States.  
Those early works evolved into sculptural pit-fired pieces that carried my emotions during a time that I was still griefing the loss of leaving my home country,  South Africa.
​Eventually, the heaviness lifted. I began seeing light, movement, and ballerinas in sheer dresses in my mind’s eye. Southern Ice porcelain became my medium of joy. Translucency, color, and light became symbols of the future.

Why Porcelain Cracks: Understanding the Real Causes 
Cracking in porcelain isn’t random—it’s usually caused by handling, design, firing, or glazing mistakes, to name a few.  Over the years, I’ve seen every kind of crack imaginable, both in my own studio and in work sent to me by students from around the world through TeachinArt.com.
Let’s break them down.

Sometimes, certain cracks are intentionally allowed. In this case, Antoinette Badenhorst stretched the clay over the balloon while it was being made. The bowl edges cracked. She, stopped it from going too far and enhanced the crack to give the bowl an organic appearance.

S-cracks are easily formed when throwing off the hump. It’s essential to ensure that the bottom of bowls thrown in this manner are compacted properly.

Antoinette Badenhorst’s beautiful, translucent, sculpted porcelain bowl was photographed during a workshop in Simonstown, South Africa.

Porcelain isn’t difficult. It’s different.
Unlike stoneware or earthenware, porcelain is worked as clay but becomes something closer to glass when fired. Understanding that single truth changes everything about how you handle, design, and fire it.

One of Antoinette Badenhorst’s exquisite sculpted porcelain bowls.

Handling Cracks in Porcelain: What to Do and What to Avoid
Porcelain becomes extremely fragile as it dries because it contains less clay, than stoneware or earthenware. 
Key rule:
* Finish shaping and altering porcelain before it passes the leather hard stage
When porcelain starts changing color as it dries, it’s  too late to alter the clay without causing problems. 
How to Prevent Handling Cracks

• Trim as soon as the base and rim are evenly moist.
• Be extra careful with rims—they crack under  little pressure on the wheel head. 
• Handle the semi-dry porcelain carefully. Even if you are successful in fixing a crack, it may show up in translucency. 

This crack was fixed, however because of the particle alignment, it still shows in the translucent pot.

The cracks in one of Antoinette’s students’ trays were caused by weak particle alignment.

​Why Porcelain Handles Crack (And How to Fix It)
Many potters struggle with porcelain handles. The real culprit in most cases is particle orientation.
Clay shrinks in unison only when its particles are aligned and compacted evenly. A handle, unconditionally of the way it is formed,  has its own direction of particles, and when you attach it to a mug, it’s like two traffic flows meeting head-on.
You need an off-ramp.
How to Attach Porcelain Handles Successfully

• Score and wet thoroughly. (remember slip particles are diluted and in disarray!)
• Attach when both parts are equally moist
• Compress and blend the joint well
• Think about handles as foreign objects that must become unified with the form

If cracks still appear, look at possible mistakes in your design and firing schedule, not just the joint.

A diagram illustrates the flow of particles when a handle is attached to a porcelain mug.

This is a good example of particles in the handle of a mug that were not aligned with those in the mug wall.

The vase’s spout, too heavy for the sheet of clay it was attached to, tore and cracked open.

Firing Cracks and Dunting in Porcelain
Dunting happens when the kiln heats or cools too fast. It can occur in bisque or glaze firing.
If a piece comes out of the kiln split cleanly in two, or cracks days later with sharp, glassy edges—the cooling cycle is usually to blame.  
Dunts in bisque ware is not   common in porcelain clay, but glaze cracking happens often.  
How to Prevent Firing Cracks

• Slow down your firing and especially the cooling schedule
• Pay special attention to cooling around quartz inversion
• Don’t rush porcelain through temperature changes

Preventing Design Cracks in Porcelain Work 
Porcelain must be formed evenly. Uneven thickness leads to slumping, tearing, and cracking.
At high temperatures, porcelain becomes  pyro plastic — it softens like glass. 

Design Tips for Porcelain

• Keep walls consistent in thickness
• Avoid heavy areas attached to thin ones. 
• Heavy clay will be drawn towards the kiln shelf and will drag thinner clay along with it. 

This beautiful crystalline plate, exposed to uneven cooling in the kiln, broke into pieces.

The glaze applied to the bowl was too thick, causing it to break into two pieces. This is a very clear example of dunting.

Over-Glazing: A common Cause of Porcelain Cracks
Too much glaze—especially inside forms—can split porcelain apart.
If glaze pools thickly in the bottom of bowls or vessels, it creates stress during firing.
​
Glazing Tips for Porcelain

• Apply thin, even glaze layers
• Avoid heavy pooling, especially  in the interior bottom of thin pots
• Spray glazing is an effective technique for applying  glaze to thin porcelain. 

Spiral Cracks in Wheel-Thrown Porcelain
There’s a  misconception that porcelain must be thrown fast to prevent collapse. In reality, it’s advisable to throw porcelain slowly, with a deliberate focus on compacting the clay particles. Spiral cracks occur when certain clay parts remain misaligned and shrink unevenly. These cracks mostly become visible during the final firing process.

How to Avoid Spiral Cracking 

• Throw slowly and meticulously. 
• Compression should be applied uniformly to the entire object, including its interior, exterior, and base, considering both the inside and outside. 
• Don’t rush. Form your pot deliberately and carefully. 

​General Tips to Prevent Base and Rim Cracks

• Trim thin porcelain before it gets too dry
• Attach a  a sponge bat on the wheel head to trim delicate rims on
• Compact the base inside and out
• Keep wall thickness even throughout

These sketches from Antoinettes porcelain online classes illustrate the various cracks that may develop in porcelain due to uneven drying.

Is the lack of compression on the interior of the bowl due to insufficient compression, or could it be that the area where the wall and base meet was left wetter than the rest of the bowl?

These are typical spiral cracks that either went unnoticed during the bisque kiln firing or occurred early in the glaze fire.

Tiny V-cracks have appeared on one of Antoinette’s students’ bowls. If these cracks are detected in time, they can be repaired.

The sketch depicts a bowl to the left, with clay particles that were not uniformly compressed.

This plate was subjected to uneven heating and cooling in the kiln, resulting in dunting.

• Antoinette Badenhorst, a renowned potter, presents online classes and hands-on workshops worldwide. In 2014, she and her husband, Koos, founded TeachingArt Online School of Art. Together with other experienced and renown teachers, they provide comprehensive online courses for potters and artists globally. These comprehensive learning experiences are meticulously designed to enhance skills, boost confidence, and foster a deeper understanding of pottery, rather than offering mere demonstrations. 

This crack is related to s-cracks and due to uneven drying.

This little cup was made by one of Antoinettes students. It looks like the crack was formed during firing. The glaze curls into the crack, therefore this is not dunting from the glaze firing.

This crack likely occurred because the base was drying on a non-absorbing bat. Alternatively, it may not have been cut loose from the bat after it was thrown.

The sketch from Antoinettes online classes with TeachinArt illustrates a V-crack that forms when the rim dries more quickly than the base.

This crack is most possibly due to glaze that was too thick for the body.

 If you enjoyed and gained something from this blog post, please share it with your friends. Unfortunately, I won’t be traveling abroad this year because I need to catch up on my studio work and am also writing a book. 
Details of my next ​porcelain workshop is available  on the Workshop page

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porcelain clay, working with porcelain, porcelain pottery, porcelain cracking, porcelain firing, porcelain handles, wheel thrown porcelain, translucent porcelain, porcelain glazing, how to prevent cracks in porcelain