Once your pottery is nicely fired, the next step is to paint it according to your desires. Painting adds a beautiful visual to the work you have done. The result will not be pleasing if you do it without completely understanding the method.
Glazing helps the pottery retain the color longer than traditional painting methods. Sometimes, some defects in glazing might occur, which leads to many interlinked issues. Though some potters create defects for aesthetic purposes, more often than not, it’s an issue.
Glaze Crazing – The Number 1 Mistake When Painting Pottery
As it’s already established that glazing has some defects, the most common mistake while painting pottery is ‘crazing.’ Crazing is a network of cracks and jagged lines on the glazed surface. It happens with the difference in the thermal expansion of the pottery and the glaze.
As the ceramics are subjected to heat, they expand and contract upon cooling. This phenomenon is called thermal expansion and shrinkage. As pottery is fragile, even a minor change will make it crack to balance the stress.
Two Types Of Crazing
Crazing, unless done for aesthetic purposes, will ruin the pottery. It has two types named immediate grazing and delayed grazing.
1. Immediate Crazing
The crazing appears immediately after removing the pottery from the kiln and happens because the glaze fits too well on the pottery. It’s expected that the glaze shrinks when cooled rather than the pottery shrinking.
2. Delayed Crazing
As the name indicates, you can only see this crazing after weeks or months. And the most common cause of this is called underfiring. Let’s see when underfiring occurs.
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When there is no uniformity in kiln heating
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When there is no accuracy in the thermocouple controller
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When the kiln is shut off early and when it is out of adjustment
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When there are variations in the heating of the kiln-sitter and kiln-shelf positions
Glazes are naturally designed to shrink less than pottery which makes them compressed. It makes them more robust and resistant to crazing.
Is It Safe To Use Crazed Pottery For Food?
Crazing significantly affects the safety and durability of the pottery. As the crazed ware absorbs moisture in the cracks, it gradually becomes a hub for bacterial growth, which leads to the need for the crockery to be consistently cleaned and sterilized.
Compared to the compressed glazes, which provide strength to the pottery, the crazed glaze makes it more brittle and susceptible to breakage. There are chances that the edges of the pottery can mix with any food or drink.
These are toxic because some glazes are made with either red or white lead. So, be conscious of the pottery you buy and ensure they have deemed a food-safe product.
How Hard Is It To Repair The Glaze Crazing?
Though glaze crazing is an issue, it can quickly be dealt with by adjusting the body of the clay. But here, too, the correction won’t be possible if the tension is too much.
Though the correction is easy, there are some things you need to focus on before deciding to proceed with it.
1. Tight Glaze Patterns
If the pattern of the glaze is crowded and tight with less than ⅛ inches gap, then understand that it is hard to correct it.
2. Unique Glaze
If you cannot alter the glaze, you can try again with other clay bodies like a simple cone of 06 to 04 white clay.
3. High Rate Of Absorption
Certain glazes have an absorption rate of over four percent. In this case, the chances of dealing with the crazing are meager.
What Are The Corrective Measures To Solve The Crazing?
Below are some ways to correct your crazing mistakes.
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More often, you can correct the glaze crazing by adding a thin layer of glaze coating. In the case of certain glazes, reducing the thickness will fix the crazing.
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Add a lot of flint to the glaze recipe, making the mesh finer. It will help in correcting the crazing.
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You should fire the kiln to the right cone for an extended period.
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Try firing the cone higher if you’re sure that the glaze won’t be severely affected. The glaze and the clay will fit better when you fire the cones higher.
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Add 200 mesh flint to the clay ware and increase the flint slowly with increased quantities, like 5%, 10 %, and 15%.
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Allow the kiln to cool down slowly. Don’t unload the kiln until the temperature goes below 200-degree celsius.
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Bisque fire the cones if you use a low fire body. Because with a soft fire body, the crazing is bound to appear.
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If the glaze you’re using is a fritted low-fire one, and if you see it crazing, then opt for a fritted glaze with a comparatively low coefficient for expanding.
Though there are many other ways of correcting your glaze crazing, this method is more straightforward and widely preferred. In this regard, to make your pottery painting easier, try the Mayco Stroke and Coat Wonderglaze. The glaze can be done with up to 3 coatings and applied on wet clay or the bisque-fired clay body.
What Are Other Mistakes That Happen While Glazing Pottery?
Crazing is not the only defect that you can experience when glazing pottery. The below table shows the other mistakes and how they happen.
Mistakes In Glazing |
Results |
Shivering |
It causes small, jagged, and sharp pieces to break from the pottery called silvers. It can mix with food and are a health hazard. |
Crawling |
It happens due to issues in adhesion, and it triggers a high index of surface tension and excessive use of powdered glaze. |
Blistering |
It occurs because of the extra glaze thickness, improper preparation of the clay body, and over-firing. |
Pin-holing |
It is caused by poorly controlled firing, the glaze composition, or can appear with grogged clay. |
Setting out |
It happens due to improper mixing of glaze or when using bacteria-infected glaze. |
Conclusion
If you are a potter dealing with the issue of glaze crazing, then you need to have two basic understandings: natural expansion and shrinkage. Correcting the crazing differs on many factors, and it’s essential to fix it because eventually, with use, it becomes a health hazard.
