Glaze Shivering & Peeling: Why It Happens and How to Fix It
Ceramic glaze is not paint. It is a glass coating that must chemically bond to the clay body during firing, and when that bond fails, the glaze shivers off in sharp flakes or peels away in sheets before the kiln even reaches temperature.
Shivering and peeling are two distinct glaze defects with different causes, different timelines, and different fixes. Treating peeling like shivering wastes glaze materials and kiln time, while mistaking shivering for peeling leaves dangerous glass shards on functional ware.
By the Numbers
Glaze Shivering and Peeling: What the Data Shows
Sources: Digitalfire Reference Library, Rhodes’ Clay and Glazes for the Potter, Ceramic Arts Network
This guide covers low-fire, mid-fire, and high-fire glaze shivering and peeling, with firing temperatures, clay body compatibility, kiln requirements, and food safety implications for each scenario.
You will learn how to tell these two defects apart by sight and timing, what causes each one at the materials-science level, and exactly how to fix both problems with specific measurements, glaze chemistry adjustments, and application corrections.
What Is Glaze Shivering and How Does It Differ from Peeling?
Glaze shivering happens after firing when the glaze flakes off the pot in sharp, glassy chips because the glaze is under too much compression relative to the clay body. Peeling happens before firing when dried glaze separates from the bisqueware surface due to poor adhesion or application problems.
The timing tells you everything. Shivering appears after the kiln cools, sometimes days or weeks later, as the compressed glaze finally releases from the clay surface. Peeling appears while loading the kiln or during the early stages of firing as the unfired glaze layer lifts away from the bisque.
According to Daniel Rhodes in Clay and Glazes for the Potter, shivering occurs when the glaze’s coefficient of thermal expansion (CTE) is significantly lower than the clay body’s CTE. The glaze shrinks less than the clay during cooling, putting the glaze layer into compression so severe that it pops off the surface.
In plain terms: the pot shrinks more than the glaze does when cooling, and the glaze eventually buckles and flies off. Peeling, by contrast, is a mechanical adhesion problem, not a thermal expansion problem.
A shivered pot leaves sharp edges that can cut fingers. This makes shivered functional ware a food safety hazard, since glaze fragments can end up in food and the exposed clay body may not be fully vitrified.
For most studio potters, the fastest way to identify which defect you have is to check when the separation happened and whether the flakes are sharp and glassy or soft and powdery.
What Causes Glaze Shivering? The Thermal Expansion Mismatch
Glaze shivering is caused by a coefficient of thermal expansion (CTE) mismatch where the glaze has a lower CTE than the clay body it sits on. Every material expands when heated and contracts when cooled, and the rate of that movement is its CTE.
In a properly fitted glaze, the glaze CTE is slightly lower than the clay body CTE, putting the glaze into mild compression. This compression strengthens the pot, similar to tempered glass. But when the CTE difference exceeds roughly 0.5 to 1.5 percentage points, the compression becomes destructive.
According to Tony Hansen’s Digitalfire Reference Library, shivering is most common in low-fire earthenware bodies fired below cone 04 (1940°F / 1060°C) where the clay body has high thermal expansion due to high silica content in the raw clay. Mid-fire and high-fire bodies are less prone to shivering because their higher firing temperatures allow the body to densify and reduce its overall expansion.
The mechanism works like this: during cooling, the clay body contracts more than the glaze layer. The glaze, now physically smaller in its relaxed state than the clay surface it is bonded to, cannot stretch to match. Stress builds at the glaze-clay interface until the glaze fractures and separates.
This only occurs when the glaze CTE is measurably lower than the body CTE across the entire cooling range from roughly 932°F (500°C) to room temperature. The condition requires a glaze formula with insufficient flux content or excess silica and alumina relative to the clay body.
If the CTE difference exists but is not corrected, the result is either shivering within hours of cooling or delayed shivering that can take weeks, with sharp-edged glaze flakes detaching from the pot surface. The fix is reformulating the glaze to increase its CTE by adding higher-expansion fluxes, as detailed in the repair section below.
Myth vs Fact
Glaze Shivering and Peeling: Common Myths Debunked
Separating fact from fiction on the most common glaze defect misconceptions
✗ Myth
Shivering and crazing are the same problem, just in different directions.
✓ Fact
They are opposites. Crazing means the glaze CTE is too high and the glaze is in tension, creating a crackle network. Shivering means the glaze CTE is too low and the glaze is in extreme compression, ejecting shards. The fixes are chemically opposite as well: crazing requires lowering glaze CTE, shivering requires raising it.
✗ Myth
A glaze that shivers is bad and should be thrown out.
✓ Fact
A shivering glaze can often be saved by adding 5-10% feldspar or other high-expansion flux to raise its CTE, or by applying it on a different clay body. The glaze chemistry is not defective; the fit is wrong for that specific clay body, and the fit can be adjusted.
✗ Myth
Peeling glaze means the bisque was fired too high and the pot is ruined.
✓ Fact
Peeling is often fixable. If the pot has not been glaze-fired yet, wash off the peeling glaze, lightly sand the bisque surface with 220-grit sandpaper to restore tooth, and reapply the glaze at the correct specific gravity. The pot is not lost unless the clay body itself is overfired and sealed.
✗ Myth
Adding more silica to a shivering glaze will fix it by making the glaze tougher.
✓ Fact
Adding silica lowers glaze CTE further and makes shivering worse. Silica has a very low thermal expansion coefficient. To raise glaze CTE and stop shivering, you must add high-expansion materials like feldspar or decrease low-expansion materials like silica and kaolin.
✗ Myth
Commercial brushing glazes never shiver because manufacturers test them.
✓ Fact
Commercial glazes can shiver on the wrong clay body. Manufacturers like Amaco and Mayco test on specific clay bodies. Using a commercial cone 6 glaze on a high-silica low-fire body or an untested stoneware can still produce shivering. Always test your clay-glaze combination on a small test tile before glazing a full kiln load.
What Causes Glaze Peeling? Application and Adhesion Failures
Glaze peeling happens when the dried glaze layer loses contact with the bisqueware surface, either curling at the edges or separating in sheets. Unlike shivering, peeling is not a chemistry problem; it is a physics problem of surface adhesion and moisture movement.
The primary cause is poor mechanical adhesion between the dry glaze particles and the bisque surface. Bisque-fired clay at cone 06 to 04 (1830-1940°F / 999-1060°C) should be porous enough to absorb water from the wet glaze, pulling glaze particles into the surface pores where they lock mechanically when dry.
If the bisque is overfired, the surface becomes too dense and sealed. Water cannot absorb, and the glaze sits on top like dust on glass, ready to peel at the slightest disturbance.
According to Mastering Cone 6 Glazes by John Hesselberth and Ron Roy, bisque fired above cone 02 (2052°F / 1122°C) on most stoneware bodies reduces porosity enough to cause glaze adhesion failure. The authors recommend bisque firing to no higher than cone 04 (1940°F / 1060°C) for most functional ware to maintain adequate absorption.
Other peeling causes include applying glaze too thickly, which creates a heavy layer that cannot hold its own weight on curved surfaces. A glaze hydrometer reading above 1.55 specific gravity for dipping glazes often produces over-thick application that peels during drying.
Dust, oil from fingers, or wax resist residue on the bisque surface also prevent adhesion. Even invisible amounts of hand oil can create a barrier that glaze cannot bond through. Wipe bisqueware with a damp sponge and allow it to dry completely before glazing.
How to Diagnose Shivering vs Peeling: A Step-by-Step Guide
Correct diagnosis determines every fix that follows. Misdiagnosing shivering as peeling leads to glaze chemistry adjustments that do nothing for adhesion, while mistaking peeling for shivering wastes time reformulating a glaze that was chemically fine.
Use the timing, the flake characteristics, and the surface underneath to tell them apart with certainty.
Step-by-Step Guide
How to Diagnose Shivering vs Peeling: Step by Step
5 steps · Takes about 10 minutes per piece
Check when the defect appeared
Did it happen after glaze firing and cooling? That points to shivering. Did it happen during drying, loading, or early kiln warmup? That points to peeling. Write down the exact timing before proceeding.
Examine the flake edges
Shivering produces sharp, glassy, razor-edged flakes that are fully melted. Peeling produces soft, crumbly, unfired glaze powder or sheets that are still matte and unfired in texture. Pick up a flake with tweezers and check the edge.
Look at the exposed clay surface
Shivering leaves a clean, smooth, sometimes slightly glossy bare clay patch where the glaze detached. Peeling leaves a rough, dusty, or powdery surface with visible dry glaze residue. The shivered surface looks like a fresh break; the peeled surface looks like it never bonded.
Check for a crackle network
Shivering often appears on the same pot that shows no crazing, or very little crazing, because the glaze is in compression, not tension. If your pot has heavy crazing, the glaze CTE is too high, and shivering is chemically impossible on that piece. Crazing and shivering do not coexist on the same glaze-clay combination.
Test the remaining glaze adhesion
Tap the pot gently with a wooden tool handle. If more glaze flakes fall off, and they are sharp glassy chips, shivering is active and ongoing. If the remaining glaze is stable but the peeled areas are at the rims or thickest glaze zones, it is likely an application or drying adhesion failure.
The pot in front of you will tell you what went wrong, but only if you check these five signs in order. Skipping the timing check and going straight to the flake examination is the most common diagnostic mistake potters make.
How to Fix Glaze Shivering: Recipe and Clay Body Solutions
Fixing shivering requires raising the glaze’s coefficient of thermal expansion until it is a close match to the clay body, or switching to a clay body with a lower CTE. The chemical fix is adding high-expansion flux materials to the glaze recipe.
In glaze chemistry terms, the oxides with the highest thermal expansion coefficients are sodium oxide (Na2O) and potassium oxide (K2O), both supplied by feldspars and frits. Oxides with the lowest CTE are silica (SiO2) and alumina (Al2O3). A shivering glaze needs more high-CTE flux and less low-CTE glass former and stabilizer.
According to the Hesselberth and Roy Unity Molecular Formula guidelines for cone 6 glazes, a well-fitted mid-fire glaze has a combined alkali oxide (KNaO) level of 0.15 to 0.30 molar equivalents in the unity formula. Shivering glazes often fall below 0.10 KNaO, meaning they lack sufficient high-expansion flux.
The practical fix for a shivering glaze recipe is adding 5-10% additional feldspar by weight. Start with 5% more potash feldspar or soda feldspar in a 100-gram test batch, mix, apply to a test tile of the same clay body, and fire. If shivering stops, you have fixed the CTE mismatch.
If it persists at 5%, increase to 8% and test again. If it persists at 10%, the clay body CTE may be unusually high, and switching to a different clay body is more cost-effective than continuing to push the glaze formula.
For commercial glazes, you cannot reformulate them. The fix is switching to a clay body the manufacturer recommends for that glaze line. Laguna and Standard Ceramic both produce mid-range stoneware bodies tested against major commercial glaze lines, and switching to a matched body eliminates shivering without any chemistry work.
There is no field test for CTE that a studio potter can perform without laboratory equipment. The practical approach is systematic testing: one variable changed at a time, fired on test tiles, with results recorded. A three-tile test comparing the original glaze, plus 5% feldspar, and plus 10% feldspar will reveal whether feldspar addition solves the shivering.
How to Fix Glaze Peeling: Application and Bisque Corrections
Fixing peeling requires restoring the bisque surface porosity, correcting glaze application thickness, and eliminating contamination. Since peeling is an adhesion problem, not a chemistry problem, the solutions are mechanical and procedural.
For bisque that is overfired or sealed, light sanding with 220-grit silicon carbide sandpaper restores surface tooth and provides mechanical grip for the glaze layer. Sand evenly over the entire surface, wipe with a damp sponge to remove dust, and allow the piece to dry fully before reglazing.
If peeling was caused by thick glaze application, check your specific gravity. Dipping cone 6 dipping glazes should measure 1.45-1.50 on a hydrometer at room temperature. If the reading is above 1.55, add water in small increments, stir thoroughly, and retest until the target range is reached.
A needle tool pushed through wet glaze to the clay surface should show a thickness of 1.5-2mm for most functional glazes. Thicker than 2mm and the glaze layer cannot hold its own weight during drying on vertical or curved surfaces. Thinner than 1mm and coverage may be insufficient after firing.
For bisqueware contaminated with dust or oil, wash the entire pot under running water with a clean sponge, using no soap. Allow it to dry for at least 24 hours before glazing. Bisque that has sat on a shelf for weeks collects airborne dust and oil from studio air. A quick rinse restores a clean surface for glaze adhesion.
If peeling occurs specifically at the rim where a double-dipped layer meets a single-dipped wall, the transition zone is too thick. Feather the dip overlap by dipping only two-thirds of the intended overlap zone on the second dip, or switch to pouring the inside glaze to avoid rim buildup entirely.
Quick Reference
Glaze Defects: Key Terms Explained
Quick reference for the technical terms used throughout this guide
The rate at which a material expands when heated and contracts when cooled, expressed as a percentage of original size per degree of temperature change. In ceramics, glaze CTE must be slightly lower than clay body CTE for a durable compression fit.
A post-firing glaze defect where the fired glaze detaches from the clay body in sharp, glassy flakes due to excessive compression from CTE mismatch. Occurs after the kiln has cooled, sometimes days or weeks later.
A pre-firing glaze defect where the unfired or drying glaze layer separates from the bisqueware surface due to poor adhesion. Occurs before or during kiln loading and warmup, not after firing.
Clay that has been fired once to a low temperature (typically cone 06-04, or 1830-1940°F / 999-1060°C) to convert it from fragile greenware into a porous, durable state that absorbs glaze water for proper adhesion.
The ratio of the density of a glaze slurry to the density of water. A specific gravity of 1.45-1.50 is the standard target for dipping glazes. Higher values mean thicker glaze with more solids per volume; lower values mean thinner glaze.
A glaze material that lowers the melting temperature of silica. Common fluxes include feldspar (sodium, potassium, calcium), whiting (calcium carbonate), zinc oxide, and lithium carbonate. Fluxes have high CTE values and are key to fixing shivering.
A glaze defect where the glaze CTE is too high relative to the clay body, putting the glaze in tension and creating a network of fine cracks. Crazing and shivering are opposite problems; a glaze cannot do both on the same clay body.
A small calibrated ceramic pyramid that bends at a specific temperature when sufficient heat work has been absorbed. Orton cones measure heat work, not temperature alone. Cone 6 (2232°F / 1222°C) is the standard mid-fire glaze temperature.
The process by which a clay body becomes dense and non-porous during firing as silica and flux materials melt and fill pore spaces. A fully vitrified clay body has under 1% absorption. Over-vitrified bisque resists glaze adhesion.
A group of aluminum silicate minerals rich in sodium, potassium, or calcium that serve as the primary flux in ceramic glazes. Potash feldspar (K2O-rich) and soda feldspar (Na2O-rich) are the most common types used to raise glaze CTE.
A primary clay mineral (Al2O3·2SiO2·2H2O) used in glazes to supply alumina and silica while keeping the glaze in suspension. EPK (Edgar Plastic Kaolin) is the most common kaolin in American glaze recipes. Kaolin lowers glaze CTE.
Silicon dioxide (SiO2), the primary glass-forming oxide in ceramic glazes. Silica has a very low thermal expansion coefficient. High-silica glazes are prone to shivering because they do not expand enough to match the clay body during cooling.
How to Prevent Both Defects Before They Happen
Preventing shivering and peeling requires testing your clay-glaze combination on a small scale before committing to production work. The single most reliable prevention method is firing test tiles for every new clay body and glaze pairing you introduce to your studio.
A proper test tile is a vertical slab of the exact clay body you plan to use, bisque-fired to your standard cone, glazed on one side with the target glaze, and fired to maturity. Check the tile for shivering after 24 hours, 1 week, and 1 month to catch delayed failures.
For peeling prevention, always bisque to the same cone every time. Consistency in bisque temperature (cone 04 at 1940°F / 1060°C for most stoneware) eliminates porosity variation as a variable. Use Orton witness cones on every bisque shelf to verify actual heat work, since kiln controllers can drift over time.
Maintain a glaze logbook with specific gravity readings, application method notes, and firing results for every glaze in your studio. When peeling or shivering appears, the logbook tells you whether the specific gravity drifted, the bisque temperature changed, or the clay body batch differs from your last successful firing.
For potters using commercial glazes, test each new glaze on your standard clay body before using it on a full kiln load. The manufacturer’s recommended clay body is a starting point, not a guarantee. Different production runs of the same clay body can vary slightly, and a test tile fired with each new batch catches these variations.
Our complete glaze troubleshooting guide covers every defect from pinholing to blistering to crawling, with systematic diagnostic steps and proven fixes for each. When shivering or peeling is just one of several recurring problems in your studio, that resource helps you trace all defects back to their root causes.
Applying glaze correctly is the other half of prevention. Our step-by-step guide to glazing ceramic pots walks through surface preparation, specific gravity adjustment, application thickness verification, and drying protocols that eliminate peeling at the source.
Advanced Questions About Glaze Shivering and Peeling Not Covered Elsewhere
Can I mix glazes from different brands on the same pot?
Quick Answer: Mixing commercial glazes from different brands is chemically risky. Each manufacturer formulates to a specific CTE range, flux system, and firing schedule. Combining an Amaco glaze with a Mayco glaze creates an unpredictable intermediate CTE and melt chemistry that may shiver on one area while remaining stable on another.
Test any mixed-brand application on a tile before using it on ware. The safe approach is layering glazes from the same product line, where the manufacturer has already tested interlayer compatibility and CTE matching across the entire series.
If you must mix brands, apply the higher-CTE glaze as the bottom layer and the lower-CTE glaze on top. This puts the bottom glaze in compression and the top glaze in mild tension, which is less likely to shiver than the reverse.
What happens if I use a cone 10 glaze in a cone 6 kiln?
Quick Answer: A cone 10 glaze fired to cone 6 (2232°F / 1222°C) instead of its rated 2381°F (1305°C) will not fully melt. The surface comes out dry, chalky, and underfired. The glaze never reaches its maturing temperature, so the fluxes do not fully dissolve the silica and alumina into a continuous glass.
This underfired glaze has poor adhesion to the clay body and may peel or flake after firing. It is also not food-safe because the unmelted surface is porous and traps bacteria. If you are working in a cone 6 kiln, use only glazes rated for cone 5-6.
Some cone 10 reduction glazes, particularly shino and celadon types, are chemically impossible to replicate at cone 6 in an electric kiln because their color development depends on the reduction atmosphere present in gas or wood firing.
Why does my glaze only shiver at the rim and not on the body?
Quick Answer: Rims experience the most extreme thermal stress because they are the thinnest section of the pot and cool fastest during kiln unloading. The rim also often has a slightly thicker glaze application from double-dipping or pouring overlap.
Faster cooling at the rim creates a steeper CTE differential between glaze and body at that location. If the glaze-body fit is borderline acceptable at the thicker, slower-cooling body, it may still fail at the rim where the thermal gradient is sharpest.
The fix is either reducing rim glaze thickness by single-dipping only, or adjusting the glaze CTE upward by 2-3% feldspar addition to eliminate the borderline mismatch entirely.
Is a shivered pot safe if the remaining glaze seems intact?
Quick Answer: No. A pot that has shivered in one area has an active CTE mismatch that may cause further shivering at any time, including after the pot is in use. The remaining glaze is under destructive compression, and additional flakes can detach during washing, heating, or normal handling.
Shivered ware should never be sold or used for food. The sharp glaze edges are a laceration hazard, and the exposed clay body beneath the shivered area may not be fully vitrified, meaning it can harbor bacteria. Discard or repurpose shivered pots as non-functional decorative items only.
If you want to attempt recovery, refiring the pot with a thin overglaze layer that has a higher CTE can sometimes bond the compression layer, but results are unreliable and the pot will never meet food-safety standards.
Can I refire a pot that peeled before the glaze firing?
Quick Answer: Yes, you can wash off all the remaining glaze, dry the bisque completely, sand lightly with 220-grit paper, and reglaze. The pot itself is not damaged. The failure was in the glaze application, not the clay body.
Make sure to identify and correct the cause of peeling before reglazing. If the bisque was overfired and sealed, sanding restores surface porosity. If the specific gravity was too high, thin the glaze. If the bisque was dusty or oily, wash and dry it.
For delicate or thin-walled pots, use a soft sponge and running water to remove glaze without stressing the bisque form. Avoid scrubbing that could erode carved details or thin edges.
Does the type of water in my studio affect glaze peeling?
Quick Answer: Very hard water with high mineral content can leave a fine salt or mineral residue on bisqueware after washing, which acts as a barrier to glaze adhesion. If your studio uses well water or municipal water with noticeable hardness, this residue can contribute to peeling.
Distilled water for the final rinse before glazing eliminates this variable. For most studios with municipal water, this is not a primary cause of peeling, but it is worth testing if you have eliminated all other variables and peeling persists across different glazes and clay bodies.
Water quality also affects glaze slurry chemistry over multiple sessions. Minerals from tap water accumulate in the glaze bucket as water evaporates and is replaced, gradually changing the glaze’s ionic balance and suspension properties.
Can slip or engobe application prevent shivering on a problematic clay body?
Quick Answer: Applying a slip or engobe layer between the clay body and the glaze can act as an intermediate CTE buffer in some cases. If the slip has a CTE between that of the clay body and the glaze, it absorbs some of the stress that would otherwise cause shivering at the glaze-body interface.
Our guide to making and using ceramic slip covers slip formulation, application thickness, and compatibility testing with different clay bodies and glazes. An engobe formulated with 20-30% frit added to the slip base creates a glass-bonding intermediate layer that improves glaze adhesion on difficult bodies.
This technique is most effective on low-fire earthenware bodies that inherently have high CTE values. A properly formulated engobe can make the difference between a shivering-prone terra cotta body and a stable glazed surface.
What is the difference between shivering and crawling?
Quick Answer: Crawling happens when molten glaze pulls away from the clay body during firing, leaving bare clay patches with rounded, melted edges where the glaze retracted. Crawling is caused by dust, oil, or over-application preventing the glaze from wetting the surface properly during melting.
Shivering happens after firing, when the glaze is fully melted and cooled, and the flakes have sharp, broken-glass edges. Crawling is a surface-tension and wetting problem during firing. Shivering is a compression fracture problem after cooling.
If the bare patch has smooth, rounded glaze edges, it is crawling. If the bare patch has sharp, jagged edges with glass-like fracture surfaces, it is shivering. The timing and edge shape are diagnostic.
Is shivering more common in reduction or oxidation firing?
Quick Answer: Shivering is equally possible in both atmospheres because CTE mismatch is a chemistry problem, not an atmosphere problem. However, reduction firing introduces additional variables that can mask or mimic shivering.
Reduction can alter the surface chemistry of the clay body by reducing iron oxide to ferrous oxide, which acts as a flux and slightly densifies the body surface. This can change the effective CTE at the glaze-body interface in ways that are difficult to predict without testing.
Electric kiln potters have one advantage: the consistent oxidation atmosphere eliminates atmosphere as a variable, making CTE testing more repeatable and predictable from one firing to the next.
Can a chipped glaze edge lead to shivering?
Quick Answer: A mechanical chip in the glaze from impact damage is not shivering and does not cause shivering, but it can look similar. The difference is that a chip has a point of impact and does not continue to spread, while shivering can progress spontaneously over time.
If the damage is limited to a specific impact point and no new flakes appear after a week of observation, it was a mechanical chip. Repairing chipped glaze on functional ceramic ware involves different techniques than fixing shivering, and the repair guide linked here covers epoxy fill, cold glaze touchup, and refiring options for different types of damage.
However, a pot with borderline shivering is more vulnerable to impact chipping because the glaze is already under extreme compression. A light bump that would not affect a properly fitted glaze can trigger a shivering cascade on an unstable pot.
Conclusion
Shivering and peeling are two different defects, and treating them as the same problem wastes time and materials. Shivering needs a glaze CTE adjustment or a clay body switch. Peeling needs a bisque porosity fix or an application correction.
Test every new clay-glaze combination on a small tile. Check specific gravity before every glazing session. And keep a logbook so you know what worked and what did not. These three habits eliminate most shivering and peeling before they reach your production kiln.
