NEWS
Focus On High-Quality Silicate (Ceramic) Materials
Optimizing Glaze Rheology for Bell/Veil Application: Dispersant and Binder Synergy
Goway offers a range of ceramic dispersants (FG-series deflocculants) and binders as part of our glaze additive product line. For glaze systems prone to foaming during preparation, see also our companion guide on Eliminating Glaze Surface Defects: Defoamer Selection (forthcoming).
Key Takeaways
- Bell and veil glazing have distinct rheology requirements: Bell glazing calls for lower viscosity (industry typical: 150–300 mPa·s at 100 rpm) for fine atomization; veil glazing needs higher extensional viscosity to maintain curtain integrity.
- Dispersants control high-shear flow: Deflocculants and polyacrylate dispersants adsorb onto particle surfaces, reduce inter-particle friction, and allow the glaze to thin under the shear of bell rotation or curtain flow.
- Binders control low-shear structure: CMC, HPMC, and organic polymeric binders create a weak gel network that stabilizes suspension during storage and provides thixotropic sag resistance after application.
- Synergy is in the ratio: Too much dispersant relative to binder leads to sedimentation and sag; too much binder leads to poor atomization and orange-peel surface. The optimal ratio must be determined through lab trial for each glaze formula.
- The Thixotropy Index (TI) is your diagnostic tool: For bell/veil applications, TI (viscosity at 20 rpm / viscosity at 100 rpm) in the range of 1.3–2.0 is generally workable — but this is a guide, not a specification.
1. Bell vs. Veil: Process Requirements and the Rheology Challenge
Bell glazing and veil (curtain) glazing are the two dominant non-contact application methods in modern tile and sanitaryware production. Both eliminate physical contact between applicator and ware — reducing mechanical stress on green bodies — but they place fundamentally different demands on glaze rheology.
1.1 Bell Glazing
In bell glazing, glaze is fed onto the center of a rapidly rotating bell cup (typically 8,000–25,000 rpm, equipment-dependent). Centrifugal force spreads the glaze into a thin film that atomizes at the bell edge, producing a fine droplet mist directed onto the ware surface. The process depends on low high-shear viscosity to achieve uniform film thickness across the bell surface and clean atomization at the edge.
Key rheological demands of bell glazing:
- Low viscosity at high shear rate (industry typical: 150–300 mPa·s at 100 rpm Brookfield,) to ensure even spreading and consistent atomization. (Reference: Industry standard glaze preparation guides; actual target depends on bell RPM, glaze density, and specific gravity.)
- Glaze density typically 1.55–1.80 g/cm³ for bell application (industry reference range) — higher density increases atomization energy demand.
- Controlled thixotropy so the glaze recovers sufficient viscosity after deposition to resist sagging on vertical or contoured surfaces.
- Minimal foaming tendency — air entrapment during high-RPM bell rotation can create pinholes in the fired glaze if not managed.
1.2 Veil (Curtain) Glazing
In veil glazing, glaze flows from an overflow trough or slot die to form a continuous falling curtain. The ware passes through the curtain on a conveyor, receiving a uniform coating thickness. The critical requirement is curtain stability — the falling film must remain coherent from the lip to the ware surface without breaking into streams or droplets.
Key rheological demands of veil glazing:
- Sufficient extensional viscosity to resist curtain thinning and break-up under gravity. This is primarily a binder function — polymers with adequate molecular weight and chain entanglement provide the extensional resistance.
- Viscosity range typically higher than bell application — industry reference range: 250–500 mPa·s at 100 rpm, though this is highly formula-dependent.
- Low sensitivity to shear history — the glaze must maintain consistent viscosity after pumping, recirculation, and passage through the slot die.
- Good leveling after deposition to eliminate curtain-induced flow lines on the ware surface.
1.3 The Common Challenge
Both processes share the same fundamental rheology paradox: the glaze must flow easily during application (high-shear, low-viscosity) but resist movement immediately afterward (low-shear, high-viscosity). This is the "ideal flow curve" problem — and it is solved through dispersant-binder synergy.
Mechanism: Centrifugal atomization
| Viscosity (100 rpm) | 150–300 mPa·s (industry ref.) |
| Density | 1.55–1.80 g/cm³ (industry ref.) |
| Thixotropy Index | 1.3–2.0 (industry ref.) |
| Critical Additive | Dispersant (high-shear control) |
| Key Defect Risk | Poor atomization, orange peel |
Mechanism: Gravity curtain
| Viscosity (100 rpm) | 250–500 mPa·s (industry ref.) |
| Density | 1.60–1.85 g/cm³ (industry ref.) |
| Thixotropy Index | 1.5–2.2 (industry ref.) |
| Critical Additive | Binder (extensional viscosity) |
| Key Defect Risk | Curtain break, flow lines |
2. The Ideal Flow Curve: What Your Glaze Rheometer Should Tell You
Glaze rheology for bell/veil application is best understood as a shear-thinning flow curve: viscosity decreases as shear rate increases. The difference between a well-formulated glaze and a problematic one lies in the shape of this curve.
2.1 The Three Critical Zones
Ideal Glaze Flow Curve — Viscosity vs. Shear Rate
Zone 1 — Storage (low shear, ~0.1–10 s−1): The glaze sits in a holding tank or recirculation system. Viscosity must be high enough to prevent sedimentation of dense particles (zirconium silicate, frit, pigments). This is the binder's territory — hydrated polymer chains form a weak three-dimensional network that supports particles against gravity.
Zone 2 — Application (high shear, ~1,000–100,000 s−1): The glaze experiences intense shear as it flows through pipes, across the bell surface, or down the curtain. Viscosity must drop sharply to allow uniform spreading, atomization, or stable curtain flow. This is the dispersant's territory — electrostatic repulsion between particles minimizes resistance to flow when shear aligns them.
Zone 3 — Post-Application Recovery (low shear, ~0.1–10 s−1): Immediately after deposition on the ware surface, the glaze must rebuild enough structure to resist sagging on vertical surfaces while still leveling sufficiently to produce a smooth fired finish. This is the synergy zone — both dispersant and binder contribute to the rate and extent of structure recovery.
2.2 Quantifying the Curve: Thixotropy Index (TI)
The simplest quantitative measure of shear-thinning behavior is the Thixotropy Index (TI), calculated as:
Where η is the apparent viscosity measured on a rotational viscometer (Brookfield or equivalent) with a suitable spindle at the specified rotational speeds.
| TI Range | Behavior | Likely Issue | Adjustment Direction |
|---|---|---|---|
| < 1.2 | Near-Newtonian | Sedimentation in tank; sagging on vertical ware; poor atomization at bell edge | Increase binder dosage; consider higher-MW binder grade |
| 1.3–2.0 | Workable range | Generally acceptable for most bell/veil operations | Fine-tune for specific glaze density and equipment parameters |
| 2.1–2.5 | Strongly thixotropic | May cause orange-peel surface; poor leveling; viscosity drift during production | Reduce binder slightly; consider lower-MW binder; verify dispersant dosage |
| > 2.5 | Excessively thixotropic | Curtain instability; gelation in holding tank; application weight fluctuation | Significant reformulation: reduce binder, increase dispersant, or switch binder type |
The TI values above are industry-typical reference ranges. Optimal TI is specific to your glaze formula, application equipment, and production speed. Lab trials under simulated production conditions are essential.
3. Dispersant Mechanism: Controlling High-Shear Viscosity
Dispersants work at the particle surface level. In a glaze suspension, particles of frit, clay, opacifier, and pigment carry surface charges that can cause them to attract one another, forming aggregates or flocs. These flocs trap water internally, increase effective particle volume fraction, and raise viscosity — particularly at low shear. Under high shear, flocs can break apart, but the process is inefficient and unpredictable.
A dispersant prevents floc formation in the first place, ensuring that the glaze behaves as a well-dispersed suspension of individual particles — which flows efficiently under shear.
3.1 How Dispersants Function
Dispersant molecules (e.g., polyacrylate, phosphate) adsorb onto particle surfaces, increasing the magnitude of the surface charge (zeta potential). When all particles carry the same charge, they repel each other — preventing aggregation.
Typical zeta potential target: |ζ| > 30 mV for stable dispersion (industry reference, DLVO theory).
Some dispersants (particularly polyacrylate types with side chains) provide steric hindrance — physically preventing particles from approaching close enough to aggregate, even if electrostatic repulsion is partially screened by dissolved ions.
Advantage: More tolerant of hard water and multivalent cations than pure electrostatic dispersants.
By breaking apart flocs, dispersants release the water that was trapped inside, making it available to lubricate particle movement. This reduces the effective solid volume fraction without changing the actual solid content.
Practical effect: Lower viscosity at a given solid content — or the ability to raise solid content without increasing viscosity.
3.2 Dispersant Types for Glaze Systems
| Type | Example Chemistry | Mechanism | Typical Dosage (% dry glaze wt.) |
Best For |
|---|---|---|---|---|
| Polyacrylate salt | Sodium polyacrylate | Electrostatic + Steric | 0.05–0.3% (industry ref.) | General-purpose glaze; tolerant of hard water |
| Inorganic phosphate | STPP, SHMP | Electrostatic + Ca²⁺ sequestration | 0.05–0.25% (industry ref.) | Soft-water systems; cost-sensitive formulations |
| Ceramic deflocculant | Silicate-phosphate blend | Electrostatic | 0.1–0.4% (industry ref.) | Medium-to-high solid content; broad mineral compatibility |
| Polycarboxylate ether | PCE superplasticizer-type | Steric-dominant | 0.05–0.2% (industry ref.) | High-solid content; rapid wetting applications |
Dosage ranges are industry-typical reference values. Optimal dosage must be determined by a five-point dosage curve test with your specific glaze formulation. Goway ceramic deflocculants, including FG-series products, offer consistent performance across various glaze mineral compositions. For product-specific recommendations, consult our ceramic dispersant solutions center.
4. Binder Mechanism: Building Low-Shear Structure
If dispersants are the "thinners," binders are the "thickeners" — but this oversimplification misses the point. Binders in glaze rheology are not just viscosity-builders; they are structural network formers that create a weak, reversible gel that breaks down under shear and rebuilds when shear is removed. This is the essence of thixotropic behavior.
4.1 How Binders Function
Water-soluble polymers like CMC (carboxymethyl cellulose) and HPMC (hydroxypropyl methylcellulose) hydrate in the aqueous phase, uncoiling their molecular chains. These extended chains entangle with one another, forming a physical (not chemical) network that traps particles and resists flow at low shear.
Under high shear, the chains align in the flow direction and disentangle — viscosity drops. When shear ceases, chains re-entangle — viscosity recovers. This is the molecular basis of thixotropy.
The hydrated polymer network increases the yield stress of the glaze — a minimum force that must be exceeded before flow begins. As long as the gravitational stress on a suspended particle is below the yield stress, the particle remains immobilized. This prevents sedimentation of high-density glaze components (zirconium silicate, some frits) during storage.
Practical target: Yield stress of 1–5 Pa is typically sufficient for most glaze densities (industry reference).
For veil glazing, binders contribute extensional viscosity — resistance to stretching deformation — which is critical for curtain stability. Higher molecular weight polymers provide greater extensional viscosity at equivalent shear viscosity.
This is why curtain break problems are often solved by switching to a higher-MW binder grade rather than simply increasing dosage.
4.2 Binder Types for Glaze Systems
| Type | Example | Key Properties | Typical Dosage (% dry glaze wt.) |
Best Application |
|---|---|---|---|---|
| CMC | Carboxymethyl cellulose (Na-CMC) |
Good water retention; moderate thixotropy; cost-effective; sensitive to multivalent cations | 0.05–0.3% (industry ref.) | Bell glazing; general curtain stability |
| HPMC | Hydroxypropyl methylcellulose | Better thermal gelation resistance; less ionic sensitivity; higher water retention | 0.05–0.2% (industry ref.) | Veil glazing; warm-climate operations |
| Organic polymeric binder | Polyacrylate/Polyacrylamide copolymer | Strong green bonding; adjustable MW; good compatibility with dispersants | 0.1–0.5% (industry ref.) | High-solid content glazes; sanitaryware |
| Xanthan gum | Biopolymer | Very high low-shear viscosity; strong yield stress at low concentration; shear-thinning | 0.01–0.05% (industry ref.) | Anti-settling in long-term storage; specialty glazes |
Dosage ranges are industry-typical reference values. Goway organic polymeric binders, including FG-ZM01A (Active Ingredient: 95-98%) and FG-ZM01D (Active Ingredient: 90-95%), offer high active content for glaze binding applications (Source: Goway Technical Data Sheet). Note: these products are primarily characterized for ceramic body binding; suitability for glaze systems should be confirmed through a specific glaze application trial. For the complete additive range, see Goway glaze additive product series.
5. The Synergy: How Dispersants and Binders Work Together
The magic — and the frustration — of glaze rheology control lies in the fact that dispersants and binders do not act independently. Changing the dosage of one shifts the effective working range of the other. This is the synergy space: the envelope of dispersant/binder combinations that produce the target flow curve.
5.1 The Competitive Adsorption Model
Both dispersants and binders can adsorb onto particle surfaces — but they compete for the same sites. A dispersant molecule that adsorbs onto a glaze particle surface contributes electrostatic or steric repulsion. A binder molecule that adsorbs onto that same surface contributes bridging between particles (flocculation by polymer bridging).
This means:
- If dispersant is added first and allowed to adsorb: It dominates the surface, and the binder is forced to act primarily in the aqueous phase — where it builds the desired low-shear network without causing bridging flocculation.
- If binder is added first: It occupies surface sites and can bridge particles into flocs that the dispersant, added later, may not fully break apart — resulting in higher-than-expected viscosity and inconsistent rheology.
5.2 Finding the Synergy Window: Dispersant-Binder Ratio Map
The relationship between dispersant dosage (D), binder dosage (B), and resulting glaze rheology can be mapped into four qualitative zones:
5.3 Synergy Effects on Application Performance
Based on industry practice and glaze application testing experience, the dispersant-to-binder ratio has observable effects on key application outcomes:
| Ratio Direction | Bell Atomization | Curtain Stability (Veil) | Anti-Sag | Leveling | Sedimentation Resistance |
|---|---|---|---|---|---|
| D ↑ / B ↓ (dispersant-heavy) |
✓ Good | ⚠ May thin | ✗ Poor | ✓ Good | ✗ Poor |
| D ↓ / B ↑ (binder-heavy) |
✗ Poor | ✓ Good | ✓ Good | ✗ Poor | ✓ Good |
| Optimal balance | ✓ Good | ✓ Good | ✓ Good | ✓ Acceptable | ✓ Good |
These are qualitative trends based on industry application experience. Actual performance depends on specific glaze composition, additive grades, water quality, and process conditions. Lab trials with your materials are essential.
6. Selection & Dosing Matrix by Glaze Type
No single dispersant-binder combination works for all glaze systems. The selection depends on the glaze's mineral composition, target application method, and specific process constraints. The table below provides starting-point recommendations for common glaze types.
| Glaze Type | Application Method | Recommended Dispersant Type | Starting Dispersant (% dry wt.) |
Recommended Binder Type | Starting Binder (% dry wt.) |
Key Adjustment Note |
|---|---|---|---|---|---|---|
| Transparent frit glaze | Bell | Polyacrylate salt | 0.10–0.20% | HPMC (low MW) | 0.05–0.10% | Minimize binder ash; prioritize dispersant for clean atomization |
| Transparent frit glaze | Veil | Polyacrylate salt | 0.10–0.15% | HPMC (medium MW) | 0.08–0.15% | Higher binder needed for curtain stability; verify no haze from binder ash |
| White zirconium glaze | Bell | Ceramic deflocculant | 0.15–0.30% | CMC | 0.08–0.15% | High ZrSiO&sub4; density (4.6 g/cm³) demands strong suspension; binder essential |
| White zirconium glaze | Veil | Ceramic deflocculant | 0.12–0.25% | CMC + HPMC blend | 0.10–0.20% | Combined binder often better than single type for curtain + suspension |
| Color glaze (pigment) | Bell | Polyacrylate salt (low ionic sensitivity) |
0.15–0.25% | CMC (low MW) | 0.05–0.12% | Pigments release multivalent ions — use dispersant tolerant of Ca²⁺/Fe³⁺ |
| Color glaze (pigment) | Veil | Polyacrylate salt (low ionic sensitivity) |
0.12–0.20% | HPMC | 0.08–0.15% | HPMC less ion-sensitive than CMC for pigment systems |
| Matt glaze (high clay) | Bell | Ceramic deflocculant + STPP blend |
0.20–0.35% | Xanthan gum (low dose) or CMC |
0.01–0.03% (xanthan) or 0.10–0.20% (CMC) |
High clay content requires strong deflocculation but also good suspension |
| Sanitaryware glaze | Bell | Polycarboxylate ether | 0.08–0.15% | Organic polymeric binder | 0.15–0.30% | Thick application layers require strong green bonding from binder |
All dosage recommendations are industry-typical starting points for lab trial evaluation. Actual optimal dosage must be determined through five-point dose-response testing with your specific glaze formulation, process water, and application equipment. Goway technical team can support tailored starting-point recommendations — request a consultation.
6.1 Decision Flowchart for Additive Selection
7. Laboratory Trial Protocol: Finding Your Optimal Ratio
The following protocol provides a systematic, seven-step method for identifying the optimal dispersant-to-binder ratio for a given glaze formula and application method.
7.1 Equipment Required
- Rotational viscometer (Brookfield or equivalent) with suitable spindle (typically #3 or #4 for glaze viscosity range)
- Stopwatch
- Analytical balance (±0.01 g)
- High-shear mixer (laboratory disperser, 1,000–3,000 rpm capability)
- Graduated cylinders (250 mL or 500 mL) — for sedimentation observation
- Constant-temperature water bath (optional but recommended — viscosity is temperature-sensitive; aim for 25 ± 1°C for all measurements)
- Test tiles (for application simulation, if available)
7.2 The Seven-Step Protocol
- Prepare baseline glaze (no additives). Weigh your standard glaze batch at the target solid content and density. Mix thoroughly with a high-shear disperser for 3 minutes at 1,500 rpm. Record the baseline viscosity at 20 rpm and 100 rpm. Note: this baseline may show very high or very low viscosity depending on glaze composition — this is expected.
- Dispersant dose-response curve (5 points). Prepare five sub-batches of the baseline glaze. Add dispersant at 0.05%, 0.10%, 0.15%, 0.20%, and 0.25% (dry glaze weight). Mix each for 3 minutes at 1,500 rpm after addition. Measure viscosity at 100 rpm for each. Select the dosage that achieves the target high-shear viscosity (industry typical for bell: 150–300 mPa·s; veil: 250–500 mPa·s). Call this Dopt.
- Binder addition at Dopt (3 points). To three fresh sub-batches at Dopt, add binder at 0.05%, 0.10%, and 0.15%. Mix for 2 minutes at 1,000 rpm, then allow 20 minutes of hydration without agitation. Measure viscosity at 20 rpm and 100 rpm. Calculate TI for each. Select the binder dosage where TI falls in the 1.3–2.0 range.
- Sedimentation stability test. Pour each candidate formulation into a 250 mL graduated cylinder. Cover and let stand undisturbed for the target storage duration (e.g., 8 hours, 24 hours, or 72 hours). Measure supernatant height and any sediment layer thickness. An acceptable formulation shows < 5% supernatant volume at the target storage duration.
- Application simulation (if equipment available). Apply the candidate formulation using laboratory-scale bell or mini-curtain apparatus, or through a simple dip-and-drain test on a vertical tile. Observe: atomization quality / curtain stability, coating uniformity, sagging on vertical surfaces, and drying uniformity. Record observations; photograph defects.
- Firing test. Fire test tiles with the candidate formulation at your standard firing cycle. Evaluate: gloss, color (compare with reference), surface smoothness, and any pinhole or crater defects. Verify that fired glaze properties meet specification. If binder ash affects gloss or color, consider a lower-ash binder grade.
- Fine-tune production parameters. Based on lab results, create two additional formulations: one at Dopt − 0.02% (to test the lower dispersant limit) and one at Bopt + 0.02% (to test the upper binder tolerance). Measure TI and sedimentation for both. The production formulation should be robust within a small tolerance window (±0.02%) — not at a knife-edge condition.
8. Troubleshooting Common Rheology Problems
Symptoms: Glaze does not atomize uniformly from the bell edge; visible droplets, threads, or uneven spray pattern.
Rheology cause: High-shear viscosity is too high — the glaze film does not thin sufficiently under bell rotation shear.
Likely root cause: Insufficient dispersant dosage; binder dominates at all shear rates. Also possible: dispersant not fully adsorbed due to incorrect addition order.
Correction: (1) Increase dispersant in 0.02% increments. (2) Verify dispersant is added before binder in the mixing sequence. (3) Check that mixing time after dispersant addition is adequate (minimum 5 minutes at >1,000 rpm). (4) If problem persists, consider switching to a dispersant with stronger steric stabilization.
Symptoms: The falling glaze curtain tears or splits into streams before reaching the ware, causing uncoated stripes.
Rheology cause: Insufficient extensional viscosity — the glaze film cannot sustain the tensile stress of gravity-driven acceleration.
Likely root cause: Binder dosage too low, binder molecular weight too low, or dispersant over-dosage suppressing network formation. Also possible: excessive glaze density creating too-rapid curtain acceleration.
Correction: (1) Increase binder dosage by 0.02–0.05%. (2) If using CMC, consider switching to a higher-MW grade or to HPMC for better extensional viscosity. (3) Reduce dispersant slightly if TI is below 1.3. (4) Reduce glaze density by 0.02–0.05 g/cm³ as a short-term measure while finalizing rheology adjustment.
Symptoms: Dense white sediment layer at tank bottom after 4–8 hours of standing; application produces glaze with variable opacity.
Rheology cause: Insufficient yield stress to suspend high-density ZrSiO&sub4; particles (ρ ≈ 4.6 g/cm³).
Likely root cause: Binder under-dosed, or binder type does not provide adequate low-shear structure. Also possible: dispersant over-dosed, suppressing the weak gel network.
Correction: (1) Increase binder by 0.03–0.05% — prioritize this over dispersant adjustment for sedimentation issues. (2) Consider adding xanthan gum at 0.005–0.01% as a supplementary suspension aid — xanthan provides strong yield stress at very low dosage. (3) If using CMC, verify water hardness; Ca²⁺ can precipitate CMC and reduce effectiveness. (4) Reduce dispersant by 0.02% to allow a degree of controlled flocculation that assists suspension.
Symptoms: Glaze drips or accumulates in a thick band at the bottom of bell-glazed ware; glaze thickness is non-uniform top-to-bottom.
Rheology cause: Insufficient structural recovery (thixotropy) after deposition — the glaze remains too fluid at low shear.
Likely root cause: Binder dosage too low relative to dispersant level; TI below 1.3. Also possible: binder hydration incomplete — adding and immediately applying without allowing full hydration.
Correction: (1) Increase binder in 0.02% increments until TI reaches ≥1.3. (2) Ensure 20–30 minutes of binder hydration time in the preparation tank before use. (3) Verify that recirculation or agitation in the holding tank is not mechanically degrading the binder polymer chains. (4) If viscosity is already at target and TI is low, consider switching to a higher-MW binder rather than simply increasing dosage of the current grade.
Symptoms: Glaze viscosity increases progressively over a shift, requiring water additions to maintain application weight; or viscosity decreases over time.
Rheology cause (increasing viscosity): Water evaporation from recirculation system (common in warm environments); incomplete initial binder hydration leading to continued swelling during production.
Rheology cause (decreasing viscosity): Dispersant continuing to adsorb over time and further reducing flocculation; shear degradation of binder polymer chains in recirculation loop.
Correction — Increasing viscosity: (1) Cover or enclose the holding tank to reduce evaporation. (2) Increase initial binder hydration time to 30+ minutes. (3) Pre-dissolve CMC/HPMC as a stock solution (1–2% concentration) rather than adding dry powder to the glaze — this ensures complete hydration before use.
Correction — Decreasing viscosity: (1) Reduce dispersant dosage slightly so the system operates closer to the flocculation threshold (more robust). (2) If using high-MW binders in a high-shear recirculation pump, consider switching to a shear-stable grade. (3) Add a small make-up dose of binder solution mid-shift if drift is predictable and consistent.
9. Frequently Asked Questions
Bell glazing typically requires glaze viscosity in the range of 150–300 mPa·s at 100 rpm (Brookfield). This is lower than the 350–600 mPa·s often used for disc-spray glazing, because the bell atomization mechanism depends on rapid, uniform centrifugal spread. However, ideal viscosity is interdependent with glaze density (typically 1.55–1.80 g/cm³ for bell applications), solid content, and bell rotational speed. A lab trial with your specific glaze formula and bell parameters is the only reliable way to establish the target viscosity window.
Dispersants and binders serve complementary functions in glaze rheology. Dispersants (such as sodium polyacrylate or ceramic deflocculants) adsorb onto glaze particle surfaces to create electrostatic repulsion, reducing inter-particle friction and lowering viscosity under high-shear conditions such as bell atomization. Binders (such as CMC, HPMC, or organic polymeric binders) hydrate in the aqueous phase to create a weak gel network that provides low-shear viscosity for suspension stability and thixotropic structure that prevents sagging after application. When properly dosed together, they produce an ideal flow curve: low viscosity under high shear (good atomization) and high viscosity under low shear (anti-settling, anti-sag). The key is finding the correct ratio for your specific glaze formula. See our dispersant solutions and glaze additive series for product options.
The Thixotropy Index (TI) is the ratio of viscosity measured at two different shear rates, typically 20 rpm and 100 rpm on a rotational viscometer. For bell/veil glazing, a TI of 1.3–2.0 is generally considered workable. A TI below 1.2 may indicate insufficient suspension stability and sag resistance; a TI above 2.5 may cause poor leveling and orange-peel surface. However, the ideal TI range is formula-specific and depends on bell configuration, glaze density, and application speed. The TI is primarily tuned through binder type and dosage adjustment.
In many cases yes, but with caveats. The ceramic deflocculants used for body slurry (such as FG-series products) can serve as dispersants in glaze preparations in principle, because the fundamental mechanism — electrostatic repulsion between suspended particles — is the same. However, glazes often contain different mineral surfaces (frits, opacifiers, colorants) and operate at lower solid content, which means the optimal dispersant type and dosage may differ significantly. Additionally, some body deflocculants contain components that can interfere with glaze development during firing. Goway offers both body dispersants and glaze-specific additives; consult our glaze additive product line for the most appropriate grade for your application.
Curtain break in veil glazing occurs when the glaze film loses cohesion during the free-fall curtain stage. Common rheology-related causes include: insufficient low-shear viscosity (the curtain thins and tears under gravity), excessive density (the curtain accelerates too quickly), or poor extensional viscosity due to inadequate polymeric binder hydration. In rheology terms, the binder may be under-dosed, the binder type may not provide adequate chain entanglement at the glaze's solid content, or the dispersant-to-binder ratio may be skewed too far toward dispersion. Typical corrections include increasing CMC/HPMC dosage by 0.02–0.05 percentage points, switching to a higher-molecular-weight grade, or reducing dispersant dosage to allow some controlled flocculation that strengthens the curtain structure.
Water hardness (dissolved Ca²⁺ and Mg²⁺ ions) affects glaze rheology through two primary mechanisms. First, multivalent cations can bridge between negatively charged particle surfaces and anionic dispersant molecules, reducing electrostatic repulsion and causing flocculation — this is why phosphate-based dispersants (like STPP) may perform poorly in hard water, as they preferentially react with Ca²⁺ rather than adsorbing on glaze particles. Second, CMC binders are particularly sensitive to Ca²⁺, which can cause precipitation or reduce hydration effectiveness. For plants with hard water (>200 ppm CaCO&sub3; equivalent), polyacrylate dispersants and HPMC binders are generally more robust choices. If hard water cannot be treated, consider adding a small amount of STPP (0.02–0.05%) as a water softener before adding the main dispersant package.
At typical dosage levels (total additives < 0.5% of dry glaze weight), well-selected dispersants and binders should not negatively affect fired surface quality. Dispersants containing sodium (polyacrylate, STPP, ceramic deflocculants) contribute Na&sub2;O to the glaze oxide balance — at typical dosages this is generally within the glaze formula's tolerance. Binders such as CMC and HPMC burn out cleanly at temperatures above ~350°C, well before glaze melting begins, leaving minimal ash (<2% of binder weight). However, for high-quality transparent glazes, even minor ash residue can produce haze. For color glazes, binder ash composition may interact with certain pigment systems. The recommended precaution is a laboratory firing test with your specific glaze formula and the proposed additive package at maximum expected dosage, comparing gloss, color (L*a*b*), and surface quality against an additive-free reference. See also our companion guide on Eliminating Glaze Surface Defects: Defoamer Selection for pinhole/crater management (forthcoming).
10. Request a Custom Rheology Optimization Trial
Get a Tailored Rheology Solution for Your Glaze Line
Every glaze formulation is unique — and so is every factory's water quality, equipment configuration, and production schedule. Goway's technical team can help you identify the optimal dispersant-binder combination for your specific glaze and application method.
What we offer:
- Starting-point dispersant and binder recommendations based on your glaze formula
- Five-point dose-response testing guidance and interpretation support
- Compatibility evaluation with your specific process water
- Complementary additive screening — including defoamers for pinhole-prone glazes
- On-site or remote technical consultation for production-scale implementation
To help us provide the most relevant recommendations, please share the following when you contact us:
Or email our technical team directly at the address listed on our contact page. Please reference this guide when inquiring.
Technical Notes & Disclaimer
- Data sources: All viscosity ranges, dosage recommendations, and TI values cited in this guide are industry-typical reference values unless explicitly attributed to a Goway product TDS. Product-specific parameters for FG-ZM01A and FG-ZM01D are sourced from Goway Technical Data Sheets. Glaze-specific dispersant products (such as GD-series references in some internal literature) are not represented in the current v2.1 product database — for glaze-optimized product specifications, contact the Goway technical team.
- Lab trials are essential: The recommendations in this guide are starting points for laboratory evaluation. Optimal dispersant and binder types, dosages, and ratios must be determined through systematic trials with your specific glaze formula, process water, application equipment, and firing cycle. No generalized guide can substitute for formulation-specific testing.
- Firing verification: All glaze additives should be verified through a complete firing trial at production conditions before full-scale adoption. Evaluate gloss, color, surface smoothness, and any defect formation against your quality standard.
- No absolute guarantees: This guide provides methodology and reference information. Actual results depend on factors beyond the scope of any general guide, including raw material batch variation, equipment condition, operator technique, and environmental conditions (temperature, humidity).
- Product availability: Not all dispersant and binder types discussed may be available in all regions or from Goway's standard product line. Contact your Goway representative for current product availability and regional sourcing.
Keyword：
Previous
More News
GOWAY INTERNATIONAL MATERIAL CO., LTD
Founded in 2009, we specialize in producing and supplying ,ceramic additives and related products, committing to supplying stable, environmentally friendly,professional and ceramic materials.
Contact UsContact Us
Company Phone/Wechat：86-0757-82131106 / +8613728575572
Company Fax：86-0757-82131106
Whatapp/skype: +8613600032377
E-mail：info6@goway-china.com
Office Address: Room C11-6, Foshan National Torch Innovation and Pioneer Park, Jihua 2nd Road, Chancheng District, Foshan City, Guangdong Province, China.
Factory Address: Nanbian Industrial Zone, Sanshui District, Foshan City Guangdong Province，China.