Have you ever made a glazed piece of pottery, only for it to dry and crack? This can be a frustrating experience for pottery makers of all skill levels, and the causes of glaze cracking are difficult to ascertain. In this article, we’ll explore what causes glaze cracking when it dries and how to prevent it from happening. We’ll also take a look at different types of glazes and discuss the role of clay bodies in glazing. Finally, we’ll go over some tips for working with glazes and look at alternatives to cracked glazing.
What Causes Glaze to Crack When Drying?
Glaze cracking or shivering when drying may be caused by a number of different factors. Glaze can shrink during the drying process, causing micro-fractures and ultimately leading to complete cracking. The type of clay body used in your pottery can also play a role in causing glaze cracking. Different clay bodies have different shrinkage rates, and when the glaze shrinks faster than the clay it can result in cracking. Additionally, the firing temperature of your piece is important, too high or low temperatures can cause glaze cracking.
Common Glaze Cracking Problems
Glaze cracking can be caused by a number of different factors, but some of the most common problems are:
- The glaze shrinks faster than the clay body.
- The glaze shrinks more than usual.
- The firing temperature is too high or too low.
- The clay body is not suited to the type of glaze being used and reacts poorly to it.
Preventing Glaze Cracking
To prevent glaze cracking, there are a few things you can do. Firstly, it’s important to choose the right clay body for the type of glaze you want to use, as this will ensure the two are compatible. Secondly, ensure you’re firing your pieces at the right temperature, as any slight changes can cause your glaze to crack. Lastly, take any special measures using the manufacturer’s directions for the glaze, such as a slow cooling rate to ensure all the chemicals have time to work their magic.
Understanding Different Types of Glazes
There are many different types of glazes available for different types of pottery. Most commercial ceramic glazes can be divided into two main categories: high-fire and low-fire. High-fire glazes require temperatures up to 2300 degrees Fahrenheit (1260 Celsius) and are generally used for stoneware and porcelain clay bodies. Low-fire glazes range from 1400 degrees Fahrenheit to 1800 degrees Fahrenheit (760-980 Celsius) and are used mainly for earthenware or terracotta clay bodies.
The Effects of Temperature on Glazing
The temperature at which you fire your piece can have a big impact on the final result of your glazed pottery. If your glazed piece has been fired at too high a temperature, then the thermal shock will cause cracks in the glaze. This can be especially common when firing a low-fire glaze at too high a temperature. On the other hand, firing at too low a temperature can lead to an unstable glaze layer, which will be prone to cracking as it dries.
The Role of Clay Bodies in Glazing
Clay bodies play an important role in preventing glaze cracking when drying. Not all clay bodies can be used with certain types of glaze, as each type of clay body will have a different shrinkage rate during the drying and firing process. For this reason, if you want to avoid large scale glazing cracking then it’s important to find the right type of clay body for the type of glaze you plan on using.
Troubleshooting Glaze Cracking Problems
If you’re experiencing persistent glaze cracking problems then you will need to do some troubleshooting. If you’re using the correct type of clay body for your glaze then you might need to adjust your firing temperatures, as this is a common cause of glaze cracking. Alternatively, it might be worth switching to a different type of glaze altogether as some types of glazes require higher firing temperatures than others.
Tips for Working with Glazes
When working with glazes there are a few tips you should keep in mind to help prevent problems such as cracking. Firstly, be sure to follow the manufacturer’s instructions carefully. Secondly, always use a kiln with an even temperature throughout, as uneven heat can cause excessive stress on your glazed pieces during drying. And finally, work quickly during the glazing process, especially on larger pieces, as this will help reduce any thermal shock that could cause cracking.
Alternatives to Cracked Glazing
If your piece has cracked despite your best efforts then you might want to consider alternative methods for finishing your pottery. One option is dipping your pottery in wax, which will help to protect it from future cracking. Another option is to use cold finishes, which do not require high firing temperatures and can help to seal any cracks from occurring again.
Glaze cracking can be incredibly frustrating for pottery makers, but with some understanding of what causes it and how to prevent it you should be able to minimise the chances of a piece cracking during drying. By choosing the right glaze and clay body and following some simple tips you can ensure that your pottery is finished with a perfect finish every time!
