Glazes that produce crawling effects are often considered to be flawed—surfaces that pull away, break apart, and expose the clay body beneath. Yet many ceramic artists are starting to use crawling glazes as a deliberate and expressive surface choice. Learn a new method for creating and controlling crawling glaze.
Questioning the Norm
Traditionally, crawling is encouraged through a physical imbalance with the glaze: excessive clay content, high surface tension, poor glaze adhesion, or surface contamination. This experiment takes a different path. Instead of relying on physical defects, it explores whether a crawling glaze can be chemically activated during preparation, producing a strong and repeatable effect at a low firing temperature of 1652°F (900°C).
My starting question was simple but specific: How can a glaze fired at a relatively low temperature develop a dramatic and consistent crawl without relying on traditional crawling methods? Rather than pushing the glaze toward failure, the goal was to understand whether chemistry itself could be used as a design tool.
Crawling glaze is composed of common ceramic materials: barium carbonate, boric acid, kaolin, silica, feldspar, and calcium carbonate. Individually, none of these materials is unusual. The key difference lies not in the recipe, but in how the glaze is mixed.
The Experiment: Boiling Water
For my experiment, instead of adding room-temperature water, boiling water was gradually added to the dry materials while blending continuously for approximately five minutes. Almost immediately, the glaze behaved differently. It thickened, expanded, and as it cooled, began to partially solidify into a gel-like mass. The texture became elastic rather than fluid—more like a soft paste than a typical glaze slurry.
What makes this especially interesting is that the change was reversible. Adding a small amount of room-temperature (approximately 20–25°C / 68–77°F) water restores the glaze to a workable liquid. This behavior indicates that the glaze is no longer acting as a simple suspension; a chemical interaction has already begun.
Why Heat Changes Everything
When boric acid and barium carbonate are mixed with cold or lukewarm water, they remain largely inactive. The glaze behaves normally, and crawling—if it appears at all—is weak and unpredictable. Boiling water changes the system entirely. The high temperature increases ionic movement in the solution and allows boric acid to partially dissociate into borate ions. These ions can then react with barium carbonate, producing the following reaction:
BaCO3 + 2 H3BO3 Ba(BO2)2 + CO2 + 3 H2O
This reaction does not occur with cold water. Boiling water acts as a chemical trigger, initiating the reaction before the glaze ever reaches the kiln.
What the Reaction Produces
Barium Borate: The most significant result of the hot-water reaction is the formation of barium borate. Barium borate functions as a low-melting flux and a glass modifier. During firing, it begins to soften and melt earlier than much of the surrounding glaze material.
As this early melting occurs, surface tension increases locally, causing the glaze to contract rather than spread. This contraction pulls the glaze into separated islands, producing the crawling effect. Unlike conventional crawling caused by poor adhesion to the clay body, this movement originates within the glaze itself.
Carbon Dioxide (CO2): Carbon dioxide is released during the reaction, primarily at the preparation stage. While most of the gas escapes before firing, its formation contributes to subtle internal disruptions within the glaze structure. These micro-voids increase internal stress during drying and early melting, helping initiate separation during firing. The CO2 does not create visible bubbles in the fired surface.
Water and Glaze Consistency: The reaction also releases additional water, which significantly affects glaze rheology. The most successful results occurred when the glaze had a thick, slightly elastic consistency—thicker than cream, but still brushable or pourable. Tests showed that:
Thin applications reduced crawling
Extremely thick applications could cause flaking
Heavy but controlled application produced strong, stable crawl islands
In many cases, the glaze developed small cracks while drying—an early indicator of internal tension that later translated into crawling.
Testing the Process
To confirm the role of boiling water, the same glaze recipe was mixed using different water temperatures:
Room-temperature water: no gel formation; weak or no crawling
Warm water 104–140°F (40–60°C): slight thickening; partial crawling
Boiling water 212°F (100°C): strong gel formation and consistent crawling
Additional material tests further confirmed the chemistry:
Removing boric acid eliminated the crawling effect
Removing barium carbonate resulted in a normal low-fire glaze
Reducing glaze thickness reduced crawl size or eliminated it entirely
These tests demonstrated that the crawling effect depends on both chemical interaction and preparation method, not on accidental imbalance.
Firing Results
Test tiles were bisque fired to 1922°F (1050°C) and glaze fired to 1652°F (900°C). At this temperature, the glaze consistently produced strong crawling patterns. Because barium borate melts early, localized contraction occurs before full glaze flow, creating high surface tension and clear separation.
The result is a crawling glaze that is predictable, repeatable, and reliable at low-fire temperatures.
A Different Way to Think About Crawling
Crawling glazes are not new. What this experiment offers is a different mechanism. By initiating chemical reactions during glaze preparation—rather than relying on defects during firing—crawling becomes a controlled design choice.
Using boiling water to activate the reaction between boric acid and barium carbonate allows ceramic artists to approach crawling not as a failure, but as an intentional and repeatable surface strategy.
the author Mohamad Soudy is an Egyptian ceramic artist whose work explores experimental glaze surfaces and sculptural ceramic forms. He was awarded the NCECA Multicultural Fellowship in 2023, and received the Egyptian Incentive Award (Fourth Medal) in 2020.
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Glazes that produce crawling effects are often considered to be flawed—surfaces that pull away, break apart, and expose the clay body beneath. Yet many ceramic artists are starting to use crawling glazes as a deliberate and expressive surface choice. Learn a new method for creating and controlling crawling glaze.
Questioning the Norm
My starting question was simple but specific: How can a glaze fired at a relatively low temperature develop a dramatic and consistent crawl without relying on traditional crawling methods? Rather than pushing the glaze toward failure, the goal was to understand whether chemistry itself could be used as a design tool.
Crawling glaze is composed of common ceramic materials: barium carbonate, boric acid, kaolin, silica, feldspar, and calcium carbonate. Individually, none of these materials is unusual. The key difference lies not in the recipe, but in how the glaze is mixed.
The Experiment: Boiling Water
For my experiment, instead of adding room-temperature water, boiling water was gradually added to the dry materials while blending continuously for approximately five minutes. Almost immediately, the glaze behaved differently. It thickened, expanded, and as it cooled, began to partially solidify into a gel-like mass. The texture became elastic rather than fluid—more like a soft paste than a typical glaze slurry.
What makes this especially interesting is that the change was reversible. Adding a small amount of room-temperature (approximately 20–25°C / 68–77°F) water restores the glaze to a workable liquid. This behavior indicates that the glaze is no longer acting as a simple suspension; a chemical interaction has already begun.
Why Heat Changes Everything
When boric acid and barium carbonate are mixed with cold or lukewarm water, they remain largely inactive. The glaze behaves normally, and crawling—if it appears at all—is weak and unpredictable. Boiling water changes the system entirely. The high temperature increases ionic movement in the solution and allows boric acid to partially dissociate into borate ions. These ions can then react with barium carbonate, producing the following reaction:
BaCO3 + 2 H3BO3 Ba(BO2)2 + CO2 + 3 H2O
This reaction does not occur with cold water. Boiling water acts as a chemical trigger, initiating the reaction before the glaze ever reaches the kiln.
What the Reaction Produces
Barium Borate: The most significant result of the hot-water reaction is the formation of barium borate. Barium borate functions as a low-melting flux and a glass modifier. During firing, it begins to soften and melt earlier than much of the surrounding glaze material.
As this early melting occurs, surface tension increases locally, causing the glaze to contract rather than spread. This contraction pulls the glaze into separated islands, producing the crawling effect. Unlike conventional crawling caused by poor adhesion to the clay body, this movement originates within the glaze itself.
Carbon Dioxide (CO2): Carbon dioxide is released during the reaction, primarily at the preparation stage. While most of the gas escapes before firing, its formation contributes to subtle internal disruptions within the glaze structure. These micro-voids increase internal stress during drying and early melting, helping initiate separation during firing. The CO2 does not create visible bubbles in the fired surface.
Water and Glaze Consistency: The reaction also releases additional water, which significantly affects glaze rheology. The most successful results occurred when the glaze had a thick, slightly elastic consistency—thicker than cream, but still brushable or pourable. Tests showed that:
In many cases, the glaze developed small cracks while drying—an early indicator of internal tension that later translated into crawling.
Testing the Process
To confirm the role of boiling water, the same glaze recipe was mixed using different water temperatures:
Additional material tests further confirmed the chemistry:
These tests demonstrated that the crawling effect depends on both chemical interaction and preparation method, not on accidental imbalance.
Firing Results
Test tiles were bisque fired to 1922°F (1050°C) and glaze fired to 1652°F (900°C). At this temperature, the glaze consistently produced strong crawling patterns. Because barium borate melts early, localized contraction occurs before full glaze flow, creating high surface tension and clear separation.
The result is a crawling glaze that is predictable, repeatable, and reliable at low-fire temperatures.
A Different Way to Think About Crawling
Crawling glazes are not new. What this experiment offers is a different mechanism. By initiating chemical reactions during glaze preparation—rather than relying on defects during firing—crawling becomes a controlled design choice.
Using boiling water to activate the reaction between boric acid and barium carbonate allows ceramic artists to approach crawling not as a failure, but as an intentional and repeatable surface strategy.
the author Mohamad Soudy is an Egyptian ceramic artist whose work explores experimental glaze surfaces and sculptural ceramic forms. He was awarded the NCECA Multicultural Fellowship in 2023, and received the Egyptian Incentive Award (Fourth Medal) in 2020.
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