Category: Wheel-throwing

Understanding and Preventing Cracks in Porcelain and Other Clay Bodies

1/26/2026

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.

A one-of-a-kind, wheel-thrown, altered, and carved translucent porcelain bowl. The sculpture features a flared, organic shape with multiple vertical folds resembling stylized leaves or petals that twist upwards from a narrow base. The exterior is a matte, unglazed cream or pale yellow color, while the interior is glazed in a smooth, glossy, pale lime green or yellow hue. The thin porcelain walls allow light to pass through, highlighting the delicate structure and the contrast between the exterior and interior colors.

One of Antoinette Badenhorst’s exquisite sculpted porcelain bowls.

This is a hand-built, altered porcelain bowl by South African ceramic artist Antoinette Badenhorst. The artist specializes in translucent porcelain pieces, often featuring carved exteriors and glazed interiors, which form part of her signature work. Each piece is part of a larger theme of

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.

A hand-built porcelain sculpture by Antoinette Badenhorst featuring two parts. A small, round, white bowl with a green interior and a jagged rim sits within a larger, flat, white porcelain sheet that resembles a leaf or a large petal. The bowl has a small V-shaped opening on one side.

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.

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.

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.

A translucent bowl that show how a fixed crack looks in translucent porcelain after is was fired.

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

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.

Showing the handle of a tray that cracked due to lack of particle alignment.

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.

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

Sketch that shows how a potters should visualize the alignment of particles.

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

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 is a clear image of a dunting crack because of too much glaze on the inside of this bowl.

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

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

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.

A golden crystalline plate that broke in 3 pieces due to uneven firing.

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

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.

A crack showing on the inside of a dried bowl.

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?

Spiral cracks showing on this white bowl with leaflike decoration.

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

Sketch showing what spiral cracks look like.

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

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

Sketches showing what various cracks look like.

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

Small cracks on the rim of this porcelain bowl.

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

Dunting cracks showing on this wheel thrown porcelain plate.

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 little porcelain cup cracked from the rim almost to the bottom.

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.

The sketch shows how a v-crack look on a mug when the rim dries faster than the body.

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

This cup shows a dunting crack that appeared after it was used for a while.

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

This crack was seen on the bottom of a vessel before it was fired.

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

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.

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

TAGS
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

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Cracking and dunting of porcelain mugs.

9/10/2020

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I was busy sorting through mugs; moving some from my showroom to my kitchen cabinets and some from my kitchen cabinets to the trash pile. If you are as sentimental as I am, any rejects first makes a round through your own kitchen and then you would look for more reasons not to dump it. Sometimes a mug will just beg you to trash it! This one time it became a pottery lesson that everyone should be aware of.
I noticed these lines in the image below in one of my porcelain coffee mugs. I knew it was the liner glaze on the inside that was cracking.
(Technical term for potters is dunting. )

Although this mug looks perfect, it had a crack in the glaze on the inside.

When glaze is applied too thick on the interior, a mug may show stain lines on the inside which are actually coffee stains that seeped into the crack and that would eventually seep out on the shelf.

When glaze is applied too thick on the interior of a mug, it may show clear cracking lines, where coffee in this case, seeped into and stained the crack.
The dunt were probably in the clay too, but my bear eye could not see it yet. I would have known over time. Chances were that hot water would have revealed that, either with an explosion of the mug (if I am really unlucky!) or with liquid just seeping out onto the table or in my lap.

It was very visible in the light colored porcelain mug. (Image above) Many mugs will not show this kind of defect and as you all know, it is the perfect place for dirt and bacteria to gather. Any well vitrified clay object can be subject to too thick layers of glaze and it can be disastrous in any clay body if the problem is not addressed.
I took the mug outside and knocked it on the cement to break it.( Yes I protected my eyes with safety glasses) and I have to tell you, it took me about 5 really hard knocks, before it broke. Did I mention that porcelain is a really strong ceramic medium?
Anyway, the way it broke shows clearly a too thick layer of liner glaze inside the mug (see image below).

A too thick glaze layer is clearly visible on the bottom of this mug shard.

How to prevent dunting in pottery.

Even walls and an even application of glaze on any functional clay object is crucial. In this case the glaze layer was too strong for the clay body. Since it is a clear glaze, it is possible that I double glazed it without realizing the mistake.
Prevent thermal shocking during the firing process. A kiln that is fired too fast or that fires unevenly may cause trouble, not only with dunting, but possibly with warping too.
Obtain knowledge of silica and its behavior in pottery clay and glazes and especially how it will behave during firing of a pottery kiln. ( Silica, often a culprit in the studio, is an interesting topic for potters to review.) See: Kilns suitable for porcelain in the near future.
Potters must make sure their glaze and clay body is a good fit for each other. There are glazes that are simply too strong for the clay body in use and instead of just shivering, it may tear and crumble a pot up into pieces.
Glazing on just one side of a piece, may cause dunting, when the stress of expansion and shrinkage on one side is stronger than the other side.
Large plates, platters and trays often tends to dunt when it is not properly set up in the kiln Learn how to fire plates.

Identify dunting in a clay object

When a crack is long and ongoing with a sharp edge, it is most certainly a dunt. This type of cracking can appear in the clay or the glaze or in both. They may appear vertical, horizontal, spiral or with a ragged edge all over the object.
If the crack is soft and rounded, it means that glaze moved and melted into the crack. The obvious observation is that the crack was there before the glaze melted. This type of crack is unrelated to dunting.

How to use pottery in the kitchen

It is important that pottery users realize that they are working with a glass-like product that can break and chip if it is abused in the kitchen.

Here are a few tips to be aware of when you buy pottery.
Always inspect your pottery directly after you received it from any ceramic artist; especially when it is shipped to you.
Make sure it does not have hidden cracks, by tapping with a wooden spoon on the rim. A cracked piece will have a dull sound.
If you are about to subject your pottery to heat or cold, ALWAYS avoid sudden temperature changes. NEVER take a bowl or casserole dish straight from the refrigerator to the oven or vise versa. Not only is it a dangerous practice in which you can get hurt, but you will most certainly loose your precious bowl.
If you observe a crack, understand when it is a dunt and when it is a flaw in the making process. A crack that was formed in the making will have rounded corners, whereas a dunt is sharp.
Be aware that there is such a thing as delayed dunting. By discussing it with the potter, you may help him/her to solve a issue that they may be unaware of.

Links
TeachinArt - Online School of Art
Wheel thrown porcelain dinnerware
Handbuilding porcelain dinnerware
AIC_IAC - International Ceramics Academy of Ceramics
MAC - Mississippi Arts Commission

Antoinette appreciate any comments. Also visit her Porcelain shopping gallery if you are interested in collecting one or more of her ceramic art pieces.

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Throwing a tall porcelain bottle - porcelain teacher Antoinette

2/5/2020

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Earlier pit fired porcelain bottle by Antoinette Badenhorst.

The throwing of a bottle requires specific planning. When working with porcelain it may take a little more planning, since the diva would not work along unless you do it "her" way. In this series of images I am showing you how I do it.

Be sure to wedge and center the clay properly The width of the dome before the opening of the clay, is an indication of how wide the bottle will be at the bottom.

Open the clay so that you have a round curve in the interior bottom. This will help to form a rounded curve at the base.

Push a dent at the bottom of the pot to be able to move a wall of clay upward.

Rather than pulling, push the clay up.

Keep pushing the "clay-wave" up right to the top. If you have to stop in- between, do so, but continue where you stopped.

Note the direction of my arm. That helps to keep the cylinder narrow and going upward instead of flaring open.
Keep pushing the clay-wave up right to the top.
Strengthen the clay rim by running over it and gently forcing the clay into the wall.(repeat this pushing process from bottom to rim at least 3 times)

The curve forms when your hands start to push the wall in and outward. Also notice how the position of my arm changes. When the interior hand pushes the clay wall outward and move it upward at the same time, a belly starts to form. At this time the outer hand (which is normally the dominant hand) will follow on the outside just below the inner hand.

When the hands change position, where the outside hand gets above the inner hand, the bellying stops and the clay move inward, closing in. Keep removing slurry and excess water all the time while throwing.

When the clay mouth becomes narrow enough for the hands to cup around the rim, it is time to collar the clay.

As the clay collar, it becomes thicker again and more clay becomes available to enclose the form and to make a spout. This is a critical time, since the clay is been worked a lot and it can easily collapse. Firm, but gentle touch and often a slightly increased speed of the wheel is necessary to keep the curve up. If you are a beginner doing pot for the first time, a 10 to 15 minute break to allow the clay to dry of some may help.

Keep collaring.

Push the clay up to form the spout.

Cut the rim straight with sharp tool if needed.

Move the clay with the one pinkie up against the other pinkie, which is in a supportive role at this stage.

Run a kidney up against the curve of the pot to remove excess slurry and to smooth the pot and allow the eye to move pleasantly and without obstruction over the curve.

Move the kidney up against the spout to help the transition between pot and spout become smooth.

The bottles below were made in the early 2000's by Antoinette.

Tips to throw a bottle successfully on the wheel.

Work very sparingly with water. More so when you throw with porcelain since the clay is thirsty and will collapse faster. Rather use little amounts of water more often that a big handful. Dipping fingers in the water is often times enough. I like to use a sponge and keep it lightly lubricated.

It takes experience to know when you need to start making the belly. Leave the pot at least a quarter of an inch thick so that there are enough clay to expand into a curve.

The top third is normally a good starting place to start narrowing the bottle.

Run a kidney (slightly bent between your fingers) from bottom to top to take out any ridges that may obstruct the flow of the curve.

Have fun, keep practicing and let me know how this method works for you. maybe you have a special tip to share here.
Keep following, because I will share more educational ceramic information here.
If you like what you see and get, please share it with your friends.

Below are comments that I copied from my previous web server. feel free to continue with comments

Thanks for the "push" vs. "pull" technique. Will try to indent and see results. Will use some porcelain at Elgin Community College this semester. Hope all is well in Mississippi with you and Koos.

Reply
Antoinette link
1/20/2014 04:47:18 pm
Great to hear from you Corky! We are doing very well while I hear you guys are cold this year! Hope your studio is warm. Let me know if the technique works for you.

Reply
Elize Kruger
1/20/2014 07:17:02 pm
Hi Antoinette, Thanks! Have you got dates yet for your Durban workshop?

Reply
Antoinette link
1/21/2014 04:14:12 am
I sent my info to some people there Elize .You can e-mail me and I will give you their names, but I guess they will have to work it through before letting me know. I have a great workshop coming up in Bryanston with Colleen Lehmkuhl and a few more in the pipeline.

Reply
Rosemary Hobson
1/21/2014 05:00:50 am
I am so looking forward to meeting you at your workshop with Colleen. Your work is very inspirational.love and light Rose Hobson.

Antoinette link
1/21/2014 07:12:35 am
Thanks Rose,I trust I will be able to teach you my techniques and you will be able to make your own beautiful works.

Reply
John Lesondak
1/21/2014 07:20:10 am
Now I'm really going to import some porcelain from France (our closest distributor). This is sheer delight to observe. But I MUST be doing it too. The photos were simply excellent (that "move the clay with one pinkie" frame is simply perfect. Thank you.

Reply
Antoinette link
1/21/2014 07:42:41 am
You are so welcome John. Next time you come back to the States, bring us a small piece of Limoges with you if you can. Just make sure it is dried in full, for flight purposes. I am very curious about it. Hope to see you in one of my future classes. Just got the next date from Mike Lalone for 2015 too..............

Reply
Greta Michelle Joachim link
1/21/2014 08:09:34 am
This is wonderful Antoinette. I am glad you decided to do this and I look forward to the e-course. How much clay are you working with in this how to?

Reply
Antoinette link
1/21/2014 09:18:23 am
Greta, it is a while since I made this specific slide presentation, but I am guessing it was about 1.5- 2 lbs. That is the beauty of porcelain: big results with a little biddy clay.
Also: it is basically put together from 2 different pots. I took the best images to get a continuous presentation.

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Understanding and Preventing Cracks in Porcelain and Other Clay Bodies

Cracking and dunting of porcelain mugs.

How to prevent dunting in pottery.

Identify dunting in a clay object

How to use pottery in the kitchen

Throwing a tall porcelain bottle - porcelain teacher Antoinette

The bottles below were made in the early 2000's by Antoinette.

Below are comments that I copied from my previous web server. feel free to continue with comments

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