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Posted by Admin on July, 20, 2026
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What Causes Crazing in Ceramics — and How Is It Cured Through Feldspar and Quartz?
The 5 fixes for crazing through feldspar and quartz:
- Increase quartz content in the body — raising the body's thermal expansion coefficient closer to the glaze's reduces the mismatch that causes crazing.
- Balance feldspar flux ratio — correct K₂O/Na₂O content in the body controls the body's own expansion behaviour relative to the glaze.
- Use consistent, mesh-graded quartz — uneven quartz particle size causes unpredictable expansion behaviour batch to batch.
- Match feldspar type to glaze chemistry — soda feldspar's lower viscosity and potash feldspar's wider firing range affect glaze fit differently.
- Verify NABL COA on every lot — batch-to-batch feldspar or quartz variation is a common, overlooked cause of intermittent crazing.
Source: Aalok Overseas Technical Laboratory, Rajasthan, India · Manufacturer & Exporter of Feldspar and Quartz Powder to 50+ Countries Since 1992 · www.feldsparindia.com
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AALOK OVERSEAS INDIA · CERAMIC DEFECT GUIDE #01
Glaze-Body Thermal Expansion Mismatch · Feldspar Flux Ratio · Quartz Mesh Consistency · NABL COA · Exporter Since 1992
REQUEST FELDSPAR & QUARTZ SAMPLE → VIEW SPECIFICATIONSWhat Is Crazing — and Why Does It Happen?
Crazing is a fine, spider-web network of cracks that forms in a fired glaze — usually visible weeks or months after firing rather than immediately. It happens because the glaze layer, upon cooling, contracts more than the ceramic body beneath it. Glass-like glazes and ceramic bodies each have their own coefficient of thermal expansion (COE); when the glaze's COE is significantly higher than the body's, the glaze ends up under tension it cannot withstand, and it cracks in a fine网 pattern to relieve that stress. Crazing does not need heat or mechanical shock to appear — it can develop slowly at room temperature as the glaze layer settles.
Crazing vs. Other Glaze/Body Defects
| DEFECT | WHAT CRACKS | PRIMARY CAUSE |
|---|---|---|
| Crazing | Glaze only (fine network) | Glaze COE too high relative to body |
| Dunting | Body (crescent cracks) | Quartz inversion stress, rapid cooling |
| Shivering | Glaze (flakes off edges) | Glaze COE too low relative to body — opposite of crazing |
6 Causes of Crazing Traceable to Feldspar and Quartz
CAUSE 01
Insufficient Quartz in the Body
Quartz raises a body's thermal expansion coefficient. A body with too little quartz expands and contracts less than the glaze layer above it, leaving the glaze under tension on cooling — a leading cause of crazing in underbodied recipes.
CAUSE 02
Incorrect Feldspar Flux Ratio in the Body
Feldspar content affects both the body's vitrification and its overall expansion behaviour. A body formulated with the wrong K₂O/Na₂O balance for its glaze can shift the body's COE just enough to trigger crazing that wasn't present in the original recipe.
CAUSE 03
Inconsistent Quartz Mesh Grading
Uneven quartz particle size changes how much of the quartz remains as free silica versus dissolves into the glassy matrix, altering the body's effective expansion coefficient batch to batch even when the nominal quartz percentage stays the same.
CAUSE 04
Mismatched Feldspar Type for the Glaze Chemistry
Soda feldspar's lower melt viscosity produces a different glass network than potash feldspar at the same firing temperature, which can shift glaze COE relative to a body designed around the other feldspar type.
CAUSE 05
Batch-to-Batch Feldspar/Quartz Variation
A supplier switching mine zones or blending inconsistent lots can silently shift flux or silica content just enough to move a recipe that was previously stable into crazing territory — without any visible change in the raw material.
CAUSE 06
High LOI Causing Micro-Porosity
Elevated loss-on-ignition in feldspar or quartz can leave micro-porosity in the fired body that subtly changes its effective expansion behaviour, compounding an already-marginal glaze fit.
Crazing Diagnostic — Symptom → Cause → Fix
| SYMPTOM | LIKELY CAUSE | FIX |
|---|---|---|
| Crazing appears weeks after firing, not immediately | Glaze COE too high relative to body — classic crazing | Increase body quartz content or adjust feldspar flux ratio |
| Crazing starts appearing after switching feldspar supplier | Batch-to-batch K₂O/Na₂O or silica variation | Demand NABL COA per shipment; verify against previous supplier's typical chemistry |
| Crazing worse on thicker-glazed pieces | Greater glaze mass amplifying the same COE mismatch | Reassess glaze application thickness alongside body/glaze fit |
| Intermittent crazing with no formulation change | Inconsistent quartz mesh grading between lots | Switch to consistently mesh-graded 200/325 quartz with sieve analysis on COA |
The Aalok Overseas Solution — Consistent Feldspar & Quartz for Crazing-Free Glazes
Mine-Direct Potash & Soda Feldspar
K₂O/Na₂O held within a tight band lot to lot, so your body's expansion behaviour stays stable — no unexplained crazing from a raw material switch you didn't make.
Consistently Graded Quartz Powder
200/325 mesh quartz with verified sieve analysis, giving predictable free-silica content and expansion behaviour batch after batch.
NABL COA on Every Shipment
Full XRF chemistry, LOI, and mesh data on every lot — not a one-time sample — so your formulation stays matched to your raw material, shipment after shipment.
Technical Support for Glaze Fit
Aalok Overseas' technical team can help match feldspar and quartz grade selection to your specific glaze chemistry to correct or prevent crazing.
Why Manufacturers Choose Aalok Overseas
Since 1992, Aalok Overseas has supplied mine-direct, NABL-certified potash feldspar, soda feldspar, quartz powder, and kaolin to ceramic manufacturers across 50+ countries. Consistency — not just chemistry on paper — is what actually prevents defects like crazing from reappearing shipment after shipment.
FAQ — Crazing in Ceramics
Q
What is the main cause of crazing in ceramic glaze?
Crazing is caused by the glaze's thermal expansion coefficient being too high relative to the body beneath it, so the glaze contracts more than the body on cooling and cracks under tension. This mismatch traces back to body and glaze formulation, particularly feldspar flux ratio and quartz content.
Q
How does quartz content affect crazing?
Quartz raises a ceramic body's thermal expansion coefficient. Increasing quartz content in an underbodied recipe brings the body's expansion closer to the glaze's, reducing the tension that causes crazing.
Q
Can crazing be fixed without changing the glaze recipe?
Yes, in many cases. Adjusting the body's quartz content or feldspar flux ratio can close the COE gap from the body side without reformulating the glaze itself, which is often simpler than redeveloping a glaze recipe.
Q
Is crazing the same as dunting?
No. Crazing is a fine network of cracks in the glaze layer only, caused by a glaze-to-body expansion mismatch. Dunting is a crack in the body itself, usually crescent-shaped, caused by thermal shock or quartz inversion stress during cooling.
Q
Why does crazing sometimes appear weeks after firing?
Glaze under tension can take time to reach the stress threshold that causes visible cracking, especially with slow moisture absorption or gradual thermal cycling in storage, which is why crazing is often called a "delayed" defect.
Related Ceramic Defect & Raw Material Guides
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