What Happens If You Put Too Much Glaze on Pottery?

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Putting too much glaze on pottery can cause problems once the piece enters the kiln. As glaze melts, an excessively thick layer may become unstable, run down the pot, bubble, crawl, or produce an uneven surface.

In severe cases, the melted glaze can reach the kiln shelf and stick the pottery to it, potentially damaging both the piece and the shelf.

However, applying several coats doesn’t automatically mean you’ve used too much glaze. Many commercial glazes are specifically designed for multiple coats. The problem is usually excessive total thickness or heavy application beyond the manufacturer’s instructions.

What Happens to Glaze in the Kiln?

Before firing, glaze is a coating of various raw materials. During firing, those materials undergo chemical and physical changes and eventually melt into the finished ceramic surface.

If the layer is excessively thick, the glaze may not behave as intended.

Instead of forming an even coating, it can become overly fluid, trap gases, pull away from the clay, or create an unusually thick surface.

1. The Glaze Can Run

One of the most obvious problems is glaze running.

As glaze melts, an overly thick application can become fluid enough to move down the sides of the pottery.

This is especially concerning near the bottom of a pot.

If the glaze reaches the kiln shelf, it can fuse the piece to the shelf.

Why is this a big problem?

A glaze-shelf connection isn’t simply a cosmetic defect. Removing the pottery afterward can damage the foot of the piece, the shelf, or both.

Always keep the kiln-contact area free of glaze.

2. Too Much Glaze Can Cause Crawling

An excessively thick glaze layer can contribute to crawling, where the glaze pulls away from sections of the pottery during firing.

The result can be irregular bare patches surrounded by areas of concentrated glaze.

Thickness isn’t the only possible cause of crawling. Surface contamination, glaze formulation, and application conditions can also matter.

For the full troubleshooting guide, see Why Is My Glaze Crawling?.

3. Bubbling and Pinholing Can Become More Likely

A heavy glaze application can make it harder for gases to escape during firing.

This can contribute to:

• Pinholes
• Blisters
• Bubbles
• Uneven surfaces

However, excessive glaze isn’t the only cause. Clay body, bisque firing, glaze chemistry, and firing schedule can all influence these defects.

See Why Is My Glaze Bubbling After Firing? for a more detailed explanation.

4. The Surface Can Become Uneven

Instead of a smooth, consistent finish, too much glaze can create:

• Thick pools
• Drips
• Heavy edges
• Uneven gloss
• Unexpected textures
• Areas with different visual thickness

This can be particularly noticeable on large flat surfaces where glaze naturally gathers.

5. The Finished Color May Look Different

Glazes aren’t simply colored paint.

When a glaze is applied much more heavily than intended, the increased thickness can change how the finished surface looks.

A color may become:

• Darker
• More opaque
• More concentrated
• More textured
• Different from the manufacturer’s sample

This is one reason test tiles are valuable when you’re trying to reproduce a specific glaze finish.

6. Your Pottery Can Stick to the Kiln Shelf

This is one of the most serious consequences of excessive glaze.

If glaze runs over the bottom of the piece and onto the shelf, it can melt and bond to the kiln shelf during firing.

Trying to remove the pottery afterward can break the piece or damage the shelf.

That’s why the foot ring or kiln-contact area should be checked carefully before loading.

Does More Glaze Always Mean a Better Color?

No.

It’s tempting to think that adding extra coats will produce a richer or stronger color, but glaze doesn’t work like ordinary paint.

Some glazes are specifically formulated for two or three coats. Adding several additional coats may simply create an overly thick layer rather than improving the appearance.

Follow the manufacturer’s recommended application thickness instead.

How Many Coats Are Too Many?

There isn’t a universal number.

One glaze might be designed for two coats, another for three, and another may require a different application method entirely.

The important question is:

How thick should this particular glaze be applied?

If you’re using a commercial glaze, start with the manufacturer’s instructions. If you’re experimenting with a glaze combination, test it before applying it to valuable pottery.

For more on application, see How Many Coats of Glaze Should You Apply to Pottery?.

What Should You Do If You’ve Already Applied Too Much?

If the pottery hasn’t been fired yet, you have a much better chance of correcting the problem.

Don’t automatically put it into the kiln.

Inspect the surface for obvious pooling, heavy areas, cracking, or glaze on the bottom. Depending on how thick the application is, you may be able to remove or reduce some of the excess.

For step-by-step troubleshooting, see How Do You Fix a Glaze That Is Too Thick?.

Can Slightly Thick Glaze Still Fire Successfully?

Yes.

A glaze being somewhat thicker than usual doesn’t guarantee that the piece will fail.

Some glaze formulas tolerate variation in application better than others. The result also depends on the clay body, firing temperature, kiln atmosphere, and glaze formulation.

That’s why it’s better to think in terms of risk and testing, rather than assuming that every slightly thick glaze application is ruined.

How to Avoid Problems From Excess Glaze

A few habits can make a big difference:

• Follow the glaze manufacturer’s application instructions.
• Don’t assume extra coats will improve the color.
• Watch for pooling around edges and lower areas.
• Keep glaze away from the kiln-contact surface.
• Allow coats to dry properly.
• Test unfamiliar glazes before using them on important work.
• Keep notes about successful glaze thickness and firing results.

Consistent application is much easier when you develop a repeatable glazing routine.

Frequently Asked Questions

Can too much glaze make pottery crack?

Excess glaze can contribute to certain glaze-related problems, but cracking has several possible causes. Glaze fit, clay body, firing conditions, and cooling can also be involved.

Can too much glaze cause glaze to run?

Yes. An excessively thick glaze layer can become more fluid during firing and run down the pottery.

Can too much glaze cause bubbling?

It can contribute to bubbling or pinholing, particularly when gases have difficulty escaping through a heavy glaze layer. However, it isn’t the only possible cause.

Can too much glaze ruin a kiln shelf?

Yes. If melted glaze runs onto the kiln shelf, it can fuse the pottery to the shelf and damage the shelf during removal.

Is three coats of glaze too much?

Not necessarily. Some commercial glazes are specifically designed for three coats. Always follow the instructions for the particular glaze you’re using.

Final Takeaway

Too much glaze doesn’t always ruin pottery, but excessive glaze thickness increases the chance of problems during firing.

The most important risks are glaze running, crawling, bubbling, uneven surfaces, and glaze reaching the kiln shelf. The best prevention is simple: follow the glaze manufacturer’s recommended application method and keep the bottom of your pottery completely free of glaze.

And if you realize the glaze is excessively thick before firing, fix it before it goes into the kiln rather than hoping the firing will correct it.