Glaze crawling is an issue which can throw a major spanner in the works when it comes to pottery, ceramics and other fired works. Crawling glaze looks like small, spidery veins in the glazed surface of the finished piece, leading to uneven and blotchy colour and texture. This issue can be notoriously difficult to work with, and can cause some major headaches for artisans and ceramic artists. But what is glaze crawling, and how can it be prevented? In this article, we’ll cover all of that and more.
The Science Behind Glaze Crawling
The term ‘glaze crawling’ refers to the runny, sometimes patchy appearance which can occur when glaze dries, or is fired. This most commonly happens when a glaze shrinks too quickly or unevenly during firing, which is affected by batch consistency, the thickness of the glaze, the amount of water and the firing curve, air flow in the kiln, type of clay being used, and much more. When a glaze shrinks it can cause microscopic wrinkles in the glazed surface, which form cracks and lead to the appearance of ‘crawls’.
Understanding the Effects of Glaze Crawling
Glaze crawling is a common problem in ceramics, pottery and porcelain. When it hits, glaze can pool in uneven shapes known as ‘birds nests’, which creates an unappealing bumpy texture that can ruin a piece. Glaze also can start to run or pull away from the piece, leaving an unsightly mess on the surface of the work. This can cause problems for artisans who are making functional objects as it affects their durability. In addition, this crawling glaze can also lead to non-consistent colors in pieces with multiple colors applied.
Causes of Glaze Crawling
Glaze crawling can be caused by using a glaze that’s too thickly applied, uneven batch consistencies, inconsistent air flow inside the kiln, or inappropriate fired temperatures. It is usually caused by too much liquid glaze being used in comparison to the amount of clay in the piece. Glaze shrinkage differ depending on the type of clay and the chemicals used in applying the glaze. If a piece of clay has too much shrinkage rate between the body and glaze, the layers could separate due to the glaze shrinking faster than the body. This creates small tears in the surface, which can be visible as crawling.
Diagnosing Glaze Crawling Problems
If you’re dealing with glaze crawling problems it may be a good idea to take a step back and look at your process. Pay attention to the ratio between clay and glaze being applied. If you have been using a higher water content with your glazes, consider reducing it. Make sure you use a consistent batch density when measuring out your ingredients. Finally, it may be necessary to adjust your firing temperature or increase air flow if that is one of your factors.
Solutions for Glaze Crawling Issues
The best way to deal with glaze crawling is prevention. Monitoring your ingredients and following a consistent firing pattern will go a long way towards avoiding this issue altogether. However, if you find yourself dealing with glaze crawling issues there are some corrective steps to take. You can tweak your drying or firing temperature, or rework you batch ratios between clay and glaze. Applying oil or burnishing coats of engobe while wet can also help reduce crawling during firing.
Preventing Glaze Crawling in the Future
Once you have identified where your glaze crawling problems lie, you can start to adjust your processes accordingly. Keep an eye out for ingredients that are not being mixed evenly, or ratios between clay and glaze that are too far off balance. Make sure you fire pieces at an appropriate temperature and do not reduce air circulation within your kiln. Finally, make sure you regularly inspect your pieces for uneven glazing.
The Benefits of Controlling Glaze Crawling
Controlling and preventing glaze crawling can have a host of benefits for anyone producing fired works. Aside from creating attractive and attractive pieces, you can also create consistent colors and textures without having to put in extra work. By controlling and preventing glaze crawling you can also extend the life of functional fired creations, and ensure they remain durable over time while retaining their aesthetic qualities.
Tips for Maintaining a Non-Crawling Glaze
The best way to ensure you don’t run into any issues with glaze crawling is to take preventative action. Here are some tips to help prevent glaze crawling problems:
- Ensure you follow consistent batch ratios when applying glazes.
- Keep an eye on ingredient amounts and mix until completely even.
- Check for clay and glaze shrinkage rate differences between layers.
- Monitor temperatures and adjust if necessary.
- Maintain steady air flow within your kiln.
- Regularly check functional pieces for any signs of stress cracking.
Glaze crawling is an issue which many ceramic artisans encounter from time to time. With some investigation into the cause of your problems, effective preventative measures and regular maintenance you can take control over your glazing process and produce beautiful, even fired works every time.
