Why Is My Glaze Crawling?

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Few things are more frustrating than opening your kiln and discovering that your beautiful glaze has pulled away from the pottery in patches.

This glaze defect is called crawling.

Instead of forming a smooth, continuous surface, the glaze separates into areas, leaving parts of the clay body exposed.

So, why is my glaze crawling?

Glaze crawling is usually related to problems with glaze application, surface preparation, drying, or the relationship between the glaze and the clay body. Fortunately, once you understand the cause, there are several ways to reduce it.

What Is Glaze Crawling?

Glaze crawling happens when a glaze coating pulls away from the ceramic surface during firing, leaving exposed areas of clay.

The glaze may appear as rounded patches, islands, or irregular sections surrounded by bare clay.

Crawling can happen during the firing process when the glaze layer doesn’t remain attached to the surface as it dries and melts.

What Causes Glaze Crawling?

There isn’t always one single cause.

Common causes include:

• Applying the glaze too thickly
• Dust or contamination on the pottery
• Poor glaze adhesion
• Glaze shrinking excessively during drying
• Incorrect glaze application
• An unsuitable glaze or clay combination
• Poorly prepared bisque ware
• Applying additional layers before previous coats have dried

Identifying which of these is happening is the first step toward preventing it.

Can Applying Too Much Glaze Cause Crawling?

Yes.

Excessive glaze thickness is one of the most common things to investigate when troubleshooting crawling.

As glaze dries, it can shrink. A very thick layer can develop enough stress that it pulls away from the ceramic surface.

Instead of forming one continuous coating, sections can separate and crawl together.

If you’re experiencing crawling, try following the manufacturer’s recommended application thickness rather than simply adding more coats.

Can Dust Cause Glaze Crawling?

Absolutely.

A dusty or dirty bisque surface can prevent the glaze from adhering properly.

Before glazing, remove loose dust from the pottery using an appropriate cleaning method.

Also keep your workspace reasonably clean.

Avoid handling the surface excessively after cleaning because oils and other contaminants from your hands can potentially interfere with glaze adhesion.

Can Oils From Your Hands Cause Crawling?

They can contribute to poor glaze adhesion.

Handling bisque ware frequently, especially on areas that will be glazed, can transfer oils or other contaminants onto the surface.

Handle pieces carefully and avoid unnecessary contact with the areas you’re about to glaze.

If you notice crawling in areas that you frequently touch, surface contamination is worth investigating.

Can Glaze Be Too Dry Before Firing?

Yes.

Glaze needs to remain properly adhered to the ceramic surface before firing.

If the dry glaze layer becomes loose, powdery, or easily disturbed, it may not fire properly.

Avoid unnecessary handling after glazing and protect pieces from dust and physical contact before loading the kiln.

Does Glaze Thickness Affect Crawling?

Definitely.

The thickness of a glaze layer can significantly affect how it behaves during drying and firing.

A glaze that’s applied too heavily may be more likely to develop crawling or other surface defects.

This is why following the manufacturer’s application instructions is so important.

More glaze doesn’t necessarily mean a better finish.

Can Multiple Glaze Coats Cause Crawling?

They can if the total glaze layer becomes too thick or if the layers don’t adhere properly.

When applying multiple coats, allow each layer to dry according to the glaze manufacturer’s instructions.

Avoid aggressively brushing over partially dried glaze because this can disturb the underlying layer.

Can the Bisque Firing Cause Crawling?

The condition of the bisque ware can affect glazing.

If the bisque surface isn’t appropriate for the glaze or hasn’t been prepared properly, glaze adhesion may suffer.

Bisque ware should be fired according to the clay manufacturer’s recommendations and should be clean and free from loose debris before glazing.

Can the Clay Cause Glaze Crawling?

Yes.

Glazes and clay bodies don’t always behave identically.

Differences in shrinkage, surface characteristics, and thermal behavior can affect how a glaze performs.

If a particular glaze repeatedly crawls on one clay body but works well on another, compatibility may be part of the problem.

Testing the glaze on your specific clay can help identify this.

Can Glaze Crawling Happen Because of the Glaze Itself?

Yes.

Some glaze formulas are naturally more prone to certain surface defects depending on their chemistry and application.

If you’ve followed the manufacturer’s instructions and still experience repeated crawling, check whether other potters have reported similar behavior for the product and whether the manufacturer provides troubleshooting recommendations.

Avoid changing several variables at once because it makes the cause harder to identify.

How Can You Prevent Glaze Crawling?

Start with the basics.

1. Clean Your Bisque Ware

Remove loose dust and debris before glazing.

2. Apply the Recommended Amount of Glaze

Don’t assume more coats will produce a better result.

Follow the manufacturer’s instructions.

3. Let Each Coat Dry

Give each coat enough time to dry before applying another.

4. Handle Pieces Carefully

Avoid unnecessary touching of areas that will be glazed.

5. Keep Your Workspace Clean

Dust and contamination can interfere with glaze adhesion.

6. Test Your Glaze

Use test tiles before applying an unfamiliar glaze to an important piece.

7. Keep Your Firing Consistent

Use the recommended firing temperature and schedule for the glaze and clay.

Can You Fix Glaze Crawling After Firing?

Once the glaze has already crawled during firing, there isn’t always an easy way to restore the original surface.

Depending on the severity of the defect, you may be able to carefully refire or apply additional compatible material, but this isn’t guaranteed to work.

Refiring without understanding the cause can sometimes make the problem worse.

It’s usually better to identify what caused the crawling and correct the glazing process on future pieces.

Should You Refire Crawled Glaze?

Not automatically.

If the crawling was caused by excessive glaze thickness, simply firing again could cause more glaze movement.

If the problem was contamination or poor adhesion, another firing may not solve it.

Before refiring, determine what happened and make sure the clay and glaze can safely tolerate another firing.

Why Does My Glaze Crawl in Some Areas but Not Others?

Localized crawling can provide an important clue.

If only certain areas are affected, consider whether those areas were:

• Touched frequently
• Dusty
• Glazed more heavily
• Layered differently
• Contaminated
• Different in thickness or shape

For example, if crawling repeatedly occurs where your fingers were holding the piece during glazing, surface contamination may be worth investigating.

Is Crawling the Same as Cracking?

No.

Crawling occurs when glaze pulls away from the ceramic surface, leaving patches of exposed clay.

Glaze cracking, often called crazing, involves fine cracks forming through the glaze surface.

They are different defects and can have different causes.

Understanding the difference makes troubleshooting much easier.

Final Thoughts: Why Is My Glaze Crawling?

If your glaze is crawling, don’t immediately blame the kiln.

The most common things to investigate are glaze thickness, surface cleanliness, contamination, drying, glaze adhesion, and clay-glaze compatibility.

Start by cleaning your bisque ware properly, applying the recommended amount of glaze, allowing each coat to dry, and handling the pottery carefully.

Most importantly, test your glaze before using it on a large batch of important work.

Once you find the right combination of clay, glaze thickness, application technique, and firing schedule, crawling becomes much easier to prevent.