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Focus On High-Quality Silicate (Ceramic) Materials
A Practical Guide to Reducing Crazing and Shivering in Glazed Ceramics
By the Goway Chemical Technical Team • Published June 2026 • 15-minute read
Crazing (fine glaze cracks) and shivering (glaze spalling) are both caused by a mismatch between the coefficient of thermal expansion (CTE) of the glaze and the ceramic body. Crazing means the glaze CTE is too low relative to the body — placing it under tensile stress on cooling. Shivering means it is too high — creating excessive compressive stress.
The fundamental fix is to bring the glaze CTE to within approximately 0.5–1.5 × 10⁻⁶/°C below the body CTE (slight residual compression is desirable). This is achieved through targeted adjustments to the oxide composition of the glaze and/or the mineral composition of the body — primarily by modifying SiO₂, Al₂O₃, alkali oxide (Na₂O/K₂O), and ZrO₂ content. Dilatometry measurement before and after any formulation change is strongly recommended.
No single additive eliminates these defects. Successful correction requires calculation, targeted formulation adjustment, and laboratory verification.
Key Facts at a Glance
- Industry guideline: Glaze CTE should be approximately 0.5–1.5 × 10⁻⁶/°C below body CTE (slight residual compression in glaze) (Ref: Parmelee, Ceramic Glazes, 3rd ed.; industry reference range)
- Crazing trigger: Glaze CTE < Body CTE; glaze experiences net tensile stress on cooling → crack network forms
- Shivering trigger: Glaze CTE significantly > Body CTE; excessive compression → adhesion failure, spalling
- Key levers for CTE reduction in glaze: Increase SiO₂ and Al₂O₃; reduce Na₂O and K₂O; add ZrSiO₄ opacifier
- Key diagnostic test: Autoclave steam test (ISO 10545-11) + dilatometry (ASTM C372 / ISO 7991)
- CTE measurement method: Differential dilatometry — simultaneous test of glaze bar and body bar; direct Δα measurement (Ref: ASTM C372)
- Risk factors beyond formulation: Excessive glaze thickness, high-porosity body, very rapid cooling rate, moisture re-absorption after firing
§1 Defect Diagnosis: Crazing vs. Shivering
Before attempting to correct either defect, the first task is to confirm which one you have — because the correction directions are opposite. Applying a crazing fix to a shivering problem will make it worse.
The glaze contracts less than the body on cooling. The body pulls the glaze into tension. Glazes are brittle and weak in tension — they crack.
The glaze contracts much more than the body on cooling. The body restrains glaze contraction — placing it under compressive stress. Excessive compression exceeds adhesion and the glaze spalls off.
1.1 Field Diagnosis Checklist
Confirming Crazing
- Fine craze lines visible under raking light or dye-penetrant inspection
- Pattern extends evenly across the field, not concentrated at edges
- Cracks may appear hours or days after firing (delayed crazing from moisture re-absorption)
- Autoclave steam test (ISO 10545-11) accelerates appearance of latent crazing
- Dilatometry shows αglaze < αbody
Confirming Shivering
- Glaze flakes or slivers detach — often with sharp, concave fracture surface
- Edges and corners of tiles most commonly affected (highest stress concentration)
- May be triggered by cutting or scoring — diagnostic: score glaze, observe shivering on scored line
- Occurs during or immediately after kiln cooling
- Dilatometry shows αglaze significantly > αbody
Goway v2.1 product specifications (TDS) include chemical composition data for ceramic body raw materials (kaolin, ball clay, calcined talc, zirconium silicate, deflocculants, binders). They do not include direct CTE measurement data for glazes or glaze-body systems. All CTE values and calculation coefficients in this guide are cited from published ceramic engineering references (P2) or designated as industry-typical reference ranges (P3). Application-specific verification by dilatometry is mandatory before production changes.
§2 Thermal Expansion Mismatch Mechanics
2.1 The Stress Formula
The magnitude of residual stress in a glaze layer due to thermal expansion mismatch can be estimated using the following simplified expression:
Eg = elastic modulus of glaze (typical: 60–80 GPa for silicate glass-ceramics) (Ref: Kingery, Bowen, Uhlmann, Introduction to Ceramics)
αb = coefficient of thermal expansion of body (×10⁻⁶/°C)
αg = coefficient of thermal expansion of glaze (×10⁻⁶/°C)
ΔT = temperature change from set point to ambient (typically ~600–700°C for single-fire tiles) (P3 industry reference)
νg = Poisson's ratio of glaze (typical: 0.20–0.25) (Ref: Kingery et al.)
This formula carries an important implication: stress is linear in both Δα and ΔT. A Δα of 2.0 × 10⁻⁶/°C over 600°C generates twice the stress of a 1.0 × 10⁻⁶/°C mismatch. Similarly, a faster kiln cooling rate that increases the effective ΔT per unit time amplifies stress even at the same final Δα.
2.2 Why a Slight Compressive Pre-stress is Preferred
The standard recommendation — that glaze CTE should be slightly below body CTE — is based on the asymmetry in the tensile and compressive strength of glaze materials. Like all ceramic glasses, fired glazes are approximately:
- Compressive strength: 700–1,000 MPa (typical) (Ref: Kingery, Bowen, Uhlmann, Introduction to Ceramics)
- Tensile strength: 30–70 MPa (typical) (Ref: Kingery, Bowen, Uhlmann)
The ratio is approximately 10:1 to 20:1. A glaze under modest compression can safely absorb the residual stress without damage. A glaze under tension has very little margin before cracking. Therefore, a CTE differential of 0.5–1.5 × 10⁻⁶/°C (glaze below body) is a practical safety window that keeps the glaze in gentle compression. A differential exceeding 2.5 × 10⁻⁶/°C in either direction typically exceeds the safe operating range and produces visible defects. (Ref: Parmelee, C.W., Ceramic Glazes, 3rd ed.; Remmey, G.B., Firing Ceramics)
2.3 Factors That Amplify Mismatch Stress
Even a moderate Δα can produce defects if other amplifying factors are present:
| Factor | Effect on Glaze Stress | How to Mitigate |
|---|---|---|
| Excessive glaze thickness | Thicker glaze accumulates more total strain energy; cracks propagate more easily | Optimise glaze specific gravity and application method; target glaze weight per m² specification |
| High body porosity (open) | Porous body offers less mechanical constraint — glaze is less supported, cracks propagate more easily once initiated | Check firing temperature and curve; ensure adequate sintering |
| Rapid kiln cooling | Increases instantaneous thermal gradient across glaze-body interface, effectively magnifying ΔT in the stress formula | Reduce cooling rate below 573°C (quartz inversion) — a well-known critical zone (P3 industry reference) |
| Moisture re-absorption post-firing | Fired body absorbs moisture and expands slightly; places glaze under additional tension — the dominant cause of delayed crazing (Ref: Singer, Singer, Industrial Ceramics) | Store tiles dry; apply moisture-resistant coating to bisque if applicable |
| Non-uniform glaze application | Thickness variations create localised stress concentrations at thin-thick boundaries | Control glaze specific gravity and Ford Cup flow time tightly at application station |
§3 CTE of Glaze Components — Oxide Contributions
The CTE of a fired glaze is largely determined by the weighted contribution of its constituent oxides. The Winkelmann-Schott (or Appen) additive approximation provides a framework for estimating CTE from oxide composition. These coefficients are established values from ceramic engineering literature.
The additive model (Winkelmann-Schott / Appen coefficients) is an approximation valid for most common silicate glaze systems. It assumes no non-linear interactions between oxide pairs. For glazes with unusual compositions (e.g., very high ZnO, high B₂O₃), independent dilatometry is required to validate calculated estimates. (Ref: Appen, A.A., Chemistry of Glass, Khimiya, Leningrad, 1970; Salmang, Scholze, Keramik)
3.1 Oxide CTE Contribution Table (Appen Coefficients)
| Oxide | Appen CTE Coefficient (×10⁻⁶/°C per mole fraction) | Directional Effect on Glaze CTE | Secondary Effects on Glaze Properties |
|---|---|---|---|
| Network Formers — typically reduce or moderate CTE | |||
| SiO₂ | 0.5 | Reduces | Increases viscosity, hardness, chemical resistance; raises maturing temperature |
| Al₂O₃ | −0.3 (network stabiliser; small negative contribution in typical compositions) | Slight reduction | Improves mechanical strength, reduces thermal shock sensitivity; raises maturing temperature, reduces gloss if over-dosed |
| B₂O₃ | −0.3 (network former at >15 mol%; fluxes at lower levels) | Slight reduction (depends on concentration) | Powerful flux at low levels; lowers surface tension; may increase thermal shock resistance |
| ZrO₂ / ZrSiO₄ | Approximately 4.0–4.6 × 10⁻⁶/°C (intrinsic CTE of ZrSiO₄) (Ref: Kingery, Introduction to Ceramics) | Reduces bulk glaze CTE as undissolved dispersed phase | Provides opacity; improves chemical resistance; raises maturing temperature. See note on mechanism below. |
| Network Modifiers — typically increase CTE | |||
| Na₂O | ~3.9 (high) | Strongly increases | Powerful flux; lowers viscosity and surface tension; may cause leaching in aggressive environments |
| K₂O | ~2.7 | Increases | Flux; contributes to brightness and gloss; generally less leachable than Na₂O |
| Li₂O | ~2.7 | Increases | Powerful flux at low concentrations; unique in that it may reduce CTE in some borosilicate formulations |
| CaO | ~1.6 | Moderately increases | Hardens glaze; improves durability; useful CTE control in matte glazes |
| MgO | ~0.6 | Slight increase | Promotes matte surface; increases hardness; found naturally in calcined talc |
| ZnO | ~0.6 | Slight increase | Opacifier at high levels; promotes crystalline (aventurine) glazes; generally good CTE control |
| BaO | ~1.9 | Increases | Useful flux; contributes to brightness; restricted in some markets for health reasons |
| PbO | ~1.0 (restricted) | Moderate | Historically used as flux/opacifier — prohibited in most current applications due to toxicity |
Appen coefficients from: Appen, A.A., Chemistry of Glass, and Salmang, H., Scholze, H., Keramik. Values listed are approximate and apply to oxide-mole-fraction-based calculations. Actual fired glaze CTE must be verified by dilatometry (ASTM C372 / ISO 7991).
3.2 The ZrSiO₄ Mechanism — Why Zirconium Silicate Can Help Reduce Crazing
Zirconium silicate (ZrSiO₄) acts as an opacifier via two mechanisms: at typical glaze firing temperatures (1050–1180°C), a portion of the ZrSiO₄ dissolves into the glaze melt. The undissolved ZrSiO₄ fraction remains as dispersed refractory particles within the fired glaze matrix. These particles have an intrinsic CTE of approximately 4.0–4.6 × 10⁻⁶/°C — significantly lower than the typical CTE of the surrounding silicate glass phase (7–9 × 10⁻⁶/°C). As a result, the presence of a dispersed low-CTE phase effectively reduces the bulk CTE of the glaze.
This means that the common practice of adding zirconium silicate as a white opacifier has a secondary benefit of reducing CTE — making it particularly useful in high-alkali glazes that would otherwise be susceptible to crazing. A Zirconium Silicate Opacifier that is sized correctly (d50 typically 0.5–1.5 µm for glazes) and of appropriate purity will both whiten the glaze and moderately reduce CTE. For guidance on selecting the correct grade for your firing temperature, see our Zirconium Silicate Grade Selection guide.
Goway zirconium silicate products (C6064: Zr(Hf)O₂ 63.5–64.5%, SiO₂ 33.13%; C6060: Zr(Hf)O₂ 59.5–60.5%, SiO₂ 34.04%; C6099: Zr(Hf)O₂ 18–20%, Al₂O₃ 80–82%) are characterised by chemical composition and whiteness at 1200°C (Source: Goway Technical Data Sheet). The TDS does not include CTE measurement data for glaze systems incorporating these products. The CTE reduction effect described above is based on the established ZrSiO₄ crystal CTE from ceramic engineering literature, and quantitative CTE impact in any specific glaze formulation must be determined by dilatometry.
§4 Adjustment Strategies for the Glaze Formulation
The glaze formulation offers more adjustment flexibility than the body formulation in most production settings. The four principal levers are:
Increase Silica (SiO₂) Content
Adding flint, quartz, or ground silica to the glaze batch directly increases SiO₂ in the fired glaze. SiO₂ has the lowest CTE contribution of common network formers (~0.5 × 10⁻⁶/°C).
Increase Alumina (Al₂O₃)
Adding calcined alumina, clay (kaolin/ball clay), or aluminium hydroxide increases Al₂O₃ content. Al₂O₃ acts as a network stabiliser and moderately reduces CTE while improving hardness.
Reduce Alkali Oxides (Na₂O, K₂O)
Na₂O and K₂O have the highest CTE contributions of common glaze oxides (~3.9 and ~2.7 respectively). Reducing soda feldspar, nepheline, or soda ash additions is the most effective single action to reduce CTE in alkali-rich glazes.
Add Zirconium Silicate (ZrSiO₄)
As described in §3.2, undissolved ZrSiO₄ particles in the fired glaze act as a low-CTE dispersed phase, reducing bulk glaze CTE while simultaneously providing opacity.
Increase Alkali Flux (Na₂O, K₂O, Li₂O)
If CTE is too low (shivering direction), cautiously increasing soda feldspar, potash feldspar, or lithium carbonate additions will raise glaze CTE. Li₂O is a powerful flux at low concentrations.
Reduce SiO₂ or Add Flux Frits
Reducing silica addition or switching to a higher-flux frit formulation raises glaze CTE. Frit manufacturers' technical data sheets typically list nominal CTE values — use these as a starting point.
Glaze formulation is a multivariate system. Changing more than one variable simultaneously makes it impossible to determine which adjustment was effective. Adjust one oxide at a time; test by dilatometry after each change; fire a batch-scale trial before full-scale production. Changes that appear to correct CTE mismatch may introduce new defects (crawling, pinholing, colour shift) if not verified through the complete firing cycle.
§5 Adjustment Strategies for the Body Formulation
In most production situations, the glaze is more easily adjusted than the body — because body formulation changes affect dimensional tolerances, pressing behaviour, firing shrinkage, and mechanical strength. However, body CTE adjustment is occasionally necessary when:
- The glaze is a purchased commercial product with a fixed composition
- The body is shared across multiple glaze lines — adjusting the body fixes the issue for all glazes simultaneously
- Glaze CTE adjustment alone would compromise glaze aesthetics (e.g., the required increase in SiO₂ would make the glaze matte)
5.1 Body CTE Adjustment Levers
| Body Ingredient | Effect on Body CTE | Typical Goway Raw Material | Goway TDS Chemistry |
|---|---|---|---|
| Kaolin (Calcined or Raw) | Relatively low CTE after firing; mullite/silica phase formation. Increasing kaolin fraction slightly lowers body CTE. | FG-K90, FG-K86 | FG-K90: Al₂O₃ 35.5%, SiO₂ 49.5% (Source: Goway TDS) FG-K86: Al₂O₃ 33.71%, SiO₂ 50.52% (Source: Goway TDS) |
| Feldspar | High K₂O/Na₂O content; feldspar-rich bodies generally have higher CTE. Reducing feldspar fraction lowers body CTE. | — | FG-K86 K₂O 3.17% (Source: Goway TDS) — kaolin with elevated K₂O; acts as a natural mild feldspathic contributor |
| Calcined Talc | MgO-rich; forms enstatite (MgSiO₃) and proto-enstatite phases on firing. Enstatite has CTE ~9–11 × 10⁻⁶/°C (Ref: Kingery et al.) — higher than typical body. Adding talc can raise body CTE. | 91#, 88#, 90#, 93# | 93#: MgO 31.09%, SiO₂ 65.7% (Source: Goway TDS). Used in floor tiles and sanitaryware bodies for CTE adjustment and whiteness. |
| Silica (Quartz/Flint) | Quartz CTE is approximately 12 × 10⁻⁶/°C below the quartz inversion (~573°C). Above inversion, cristobalite phase can form in high-silica fired bodies, with CTE ~21–23 × 10⁻⁶/°C. Net effect on sintered body CTE depends on phase composition after firing. Generally, increasing silica raises fired body CTE at room temperature due to residual quartz contribution. (Ref: Kingery, Introduction to Ceramics) | — | — |
| Ball Clay | Similar to kaolin on firing. High plasticity ball clays introduce more organic matter (L.O.I) — which burns out, increasing porosity and changing body mechanics. CTE effect is secondary to mullite-silica phase balance. | FG-B88, FG-B82 | FG-B88: Al₂O₃ 30.5%, SiO₂ 54.2% (Source: Goway TDS) FG-B82: Al₂O₃ 32.5%, SiO₂ 50.9%, Fe₂O₃ 1.0% (Source: Goway TDS) |
Body CTE changes affect dimensional tolerances, warpage, and mechanical strength. Any body formulation adjustment must be validated through a full production trial including dimensional checks, strength testing (EN ISO 10545-4), and glaze quality evaluation.
For context on how body binder selection and the spray drying process interact with body porosity (which influences glaze stress behaviour), refer to our Improve Ceramic Green Strength: Binder Selection guide — body green strength, granule quality, and pressed-body porosity are all upstream variables that affect how the fired body responds to glaze-body CTE mismatch stress.
§6 Practical CTE Calculation and Test Methods
6.1 The Appen Additive Calculation (Mole Fraction Method)
For a first approximation of glaze CTE from oxide composition, the Appen additive model calculates:
ai = Appen CTE coefficient for oxide i (from Table in §3.1)
Sum is taken over all oxides in the Seger unity mole formula
Worked Example (P3 Estimation — for illustration only):
A simple opaque white tile glaze contains (approximate mole fractions):
SiO₂: 0.55 × 0.5 = 0.28
Al₂O₃: 0.10 × (−0.3) = −0.03
Na₂O: 0.08 × 3.9 = 0.31
K₂O: 0.05 × 2.7 = 0.14
CaO: 0.08 × 1.6 = 0.13
ZnO: 0.04 × 0.6 = 0.02
ZrO₂: 0.04 × 4.0 = 0.16 (undissolved ZrSiO₄ fraction)
Estimated αglaze ≈ 1.01 × 10⁻⁶ sum — but note this model is summed per mole, not per 10⁻⁶ unit. Final value in practice depends on proper unit conversion per Appen's original publication.
6.2 Dilatometry — The Definitive Measurement
The gold standard for CTE characterisation of glazes and bodies is differential dilatometry (simultaneous measurement of glaze specimen and body specimen):
Prepare Test Specimens
Prepare fired glaze specimens (typically 50 × 6 × 6 mm bars) and matching body specimens (same dimensions) from production-equivalent materials fired at the target temperature and hold time. Grinding the surfaces flat and parallel is critical to dilatometry accuracy.
Run Differential Dilatometry
Insert glaze bar and body bar simultaneously into the differential dilatometer (push-rod type or optical). Heat from room temperature to 900°C at a standard controlled rate (typically 3–5°C/min). Record displacement vs. temperature curves for both specimens. (Ref: ASTM C372 Standard Test Method for Linear Thermal Expansion of Porcelain Enamel and Glaze; ISO 7991)
Calculate Mean CTE and Δα
Calculate mean CTE (α) for each specimen over the range 25–400°C (common reference range for ceramic tile). Calculate Δα = αbody − αglaze. A positive Δα confirms the glaze is under compression (desirable). Negative Δα confirms tensile stress (crazing risk). Δα exceeding 2.5 × 10⁻⁶/°C in either direction warrants immediate formulation review. (P3 industry-typical threshold)
Identify Set Point (Fixing Temperature)
From the dilatometry trace, identify the "set point" — the temperature below which the glaze transitions from viscous relaxation to elastic behaviour. All thermal expansion mismatch stress that matters for crazing and shivering accumulates below this temperature. For most commercial tile glazes, the set point is in the range of 600–700°C. (Ref: Parmelee, Ceramic Glazes)
Steam Test Verification (ISO 10545-11)
As a rapid plant-floor supplement to dilatometry, apply the autoclave steam test: place 10 representative fired samples in a pressure cooker at 100–120°C for 30–60 minutes (or per ISO 10545-11 procedure). Inspect for crazing using dye penetrant. Pass/fail criterion: no crazing visible at 10× magnification. This test does not replace dilatometry but provides a practical go/no-go check before production scale-up.
Iterate and Re-test
After each formulation adjustment (glaze or body), repeat dilatometry on new fired specimens. Do not assume additive-model calculations alone are sufficient — the Appen model has ±0.5–1.0 × 10⁻⁶/°C accuracy, and a target Δα of 0.5–1.5 × 10⁻⁶/°C requires measurement precision that the calculation alone cannot provide.
Production Trial and Hold
After dilatometry confirms the target Δα, run a minimum of one full kiln car (or equivalent batch size) under production conditions. Hold product for 72 hours before release — delayed crazing from moisture re-absorption will manifest within this window. Only release to storage after visual inspection and steam test pass. The spray drying and granule preparation process also affects fired body porosity; see our Spray Drying Energy Optimization guide for relevant upstream process parameters.
§7 Selection & Adjustment Matrix
| Defect Type & Severity | CTE Situation | Primary Glaze Action | Secondary/Body Action | Verification Priority |
|---|---|---|---|---|
| Mild crazing Fine network, appears on cooling |
Δα estimated 0–0.5 × 10⁻⁶/°C (glaze slightly above body) | Add 3–5% ZrSiO₄ opacifier to glaze; or increase SiO₂ by 2–4 mole % | Reduce cooling rate through quartz inversion zone | Steam test after each adjustment; dilatometry to confirm Δα |
| Moderate to severe crazing Immediate on cooling, or extensive network |
Δα estimated 0.5–2.0 × 10⁻⁶/°C (glaze significantly above body) | Reduce Na₂O/K₂O alkali content by 15–25% molar; increase SiO₂ and/or ZrSiO₄ | If body CTE is too high: review feldspar fraction; increase kaolin proportion | Dilatometry mandatory; full kiln trial before scale-up |
| Delayed crazing Appears days/weeks after production |
Borderline CTE mismatch + moisture expansion | Check CTE by dilatometry — even borderline Δα ≈ 0 can cause delayed crazing if body absorbs moisture and expands | Improve body firing temperature / density to reduce water absorption; review storage conditions | ISO 10545-3 (water absorption) + dilatometry; check fired body porosity |
| Mild shivering Edge/corner chipping, localised spalling |
Δα: glaze moderately above body CTE | Reduce ZrSiO₄ (if high loading is reducing glaze CTE excessively); add soda feldspar or potash feldspar to glaze | If body CTE is too low: review silica addition; add calcined talc (MgO source) | Dilatometry; confirm glaze CTE ≥ body CTE − 1.5 × 10⁻⁶/°C |
| Severe shivering Widespread spalling, flakes during cutting |
Δα: glaze significantly above body CTE (≥ 2.5 × 10⁻⁶) | Significant reformulation: reduce all high-CTE flux inputs; reformulate against a body-specific CTE target | Consider body CTE adjustment via talc addition; review all raw material oxide contributions | Dilatometry mandatory at every formulation iteration; steam test; cut-edge inspection |
| High-alkali glaze on low-silica body Crazing risk from composition mismatch |
Predicted high Δα from oxide composition | Add intermediate-CTE flux (CaO via calcium carbonate or wollastonite) to partially replace Na₂O; add ZrSiO₄ for dual CTE reduction + opacity | Increase silica in body to raise body CTE toward glaze CTE | Calculate Appen estimate; verify by dilatometry before production trial |
| New raw material batch causes sudden crazing | CTE changes due to raw material variation | Test new raw material by XRF/XRD; compare K₂O/Na₂O/CaO in feldspar batch; run incoming CTE check on glaze fired with new material | Set incoming QC thresholds for Na₂O, K₂O in feldspar and clay raw materials | XRF analysis; dilatometry on glazes prepared with new vs. old batch |
| Glaze crazing after glaze thickness increase | Same formulation, only glaze application changed | Reduce glaze specific gravity and/or application weight to return to original thickness; or add ZrSiO₄ to reduce CTE and compensate for thickness effect | Review glaze application method; calibrate glaze application weight per m² | Steam test; check glaze weight per tile vs. specification |
All adjustment directions are qualitative guidance based on well-established ceramic engineering principles (P2) and industry practice (P3). Quantitative adjustment amounts depend on the specific glaze and body compositions. Laboratory-scale trials with dilatometry verification are required before production implementation.
§8 Laboratory Validation Protocol
The following 7-step protocol guides a systematic investigation from symptom to verified fix:
Collect Defect Samples and Document
Collect minimum 20 tiles exhibiting the defect plus 20 defect-free tiles from the same production run. Record: firing date, kiln car position, glaze application line, batch numbers of all raw materials. Photograph defects under raking light and 10× magnification.
Confirm Defect Type (§1 Checklist)
Apply the diagnostic checklist from §1. If uncertain between crazing and shivering, apply dye-penetrant to a defective tile and examine crack morphology. Run ISO 10545-11 steam test on defect-free tiles to check for latent crazing susceptibility.
Run XRF on Glaze and Body (if not recently done)
Obtain XRF oxide analysis of the current glaze and body. Calculate the Seger unity mole formula for the glaze. Apply the Appen additive model (§6.1) to estimate current glaze CTE. Compare with body CTE estimated from known body composition or measured dilatometry data.
Dilatometry of Current Glaze and Body
Prepare fired bars of the current glaze (cast from melt, or ground from fired tile glaze layer if thick enough) and body. Run differential dilatometry per ASTM C372 / ISO 7991. Record actual Δα = αbody − αglaze. Compare with Appen model prediction to calibrate the model for your specific system.
Design Glaze Adjustment Experiment
Based on confirmed Δα and defect type, design a minimum 3-point formulation trial (conservative/moderate/aggressive adjustment of the primary lever identified in §4 or §5). Prepare test glazes. Apply to standardised test tiles at the production-equivalent specific gravity and application weight. Fire at production temperature.
Dilatometry and Steam Test on Trial Glazes
For each formulation variant, run dilatometry on fired glaze bars. Record Δα. Apply steam test (ISO 10545-11) to fired tiles. Identify the formulation that achieves target Δα of 0.5–1.5 × 10⁻⁶/°C (glaze below body) and passes steam test.
Production Trial and 72-Hour Hold
Fire a full kiln car (or equivalent batch) with the optimised formulation. Hold for 72 hours minimum before inspection. Perform: visual inspection, steam test, scratch adhesion check (for shivering), cut-edge inspection. If all pass, update the production Standard Operating Procedure with the new formulation, target Δα, and dilatometry schedule.
§9 Troubleshooting
Crazing eliminated in lab trial, but reappears in production after several days
Shivering occurs only at cut edges and tile corners — centre of tile is fine
Adding more ZrSiO₄ increased opacity but did not reduce crazing
Glaze passes dilatometry test but still crazes on the production floor
Simultaneously observing both crazing and shivering on different parts of the same tile
§10 Frequently Asked Questions
Request a Thermal Expansion Matching Consultation
Crazing and shivering corrections benefit greatly from expert review of both glaze and body chemistry together. Goway's technical team works with ceramic producers to identify the specific formulation adjustments that resolve CTE mismatch while preserving glaze aesthetics and body mechanical performance.
To submit an inquiry, visit our Zirconium Silicate Opacifier product page (/products_detail/11.html) and use the inquiry form. Please include the information below to enable a more targeted response.
Please reference this guide ("Crazing and Shivering Guide") when submitting your inquiry. Providing existing XRF data and dilatometry records (if available) enables more precise recommendations.
Related Resources
- Zirconium Silicate Opacifier — C6064 (Zr(Hf)O₂ 63.5–64.5%), C6060, C6099 product specifications (visit /products_detail/11.html)
- Zirconium Silicate Grade Selection — grade selection methodology for opacifier applications (visit /News_detail/154.html)
- Improve Ceramic Green Strength: Binder Selection — body binder selection affects body porosity, which influences glaze-body stress response (visit /News_detail/158.html)
- Spray Drying Energy Optimization — upstream process parameters that affect fired body porosity and glaze application quality (visit /News_detail/155.html)
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