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Posted by Admin on July, 12, 2026
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How to Get Fine Glaze in Ceramics Through Feldspar, Quartz & Kaolin?
The 6 steps to fine ceramic glaze through Feldspar, Quartz & Kaolin:
- Use K-Feldspar Fe₂O₃ <0.06%, 325 Mesh — provides clean, uniform glass phase with no iron-related discolouration or gas-driven surface defects.
- Use Na-Feldspar Na₂O 10%+, 325 Mesh — lower melt viscosity keeps the glaze fluid longer, enabling complete surface self-levelling and pinhole healing.
- Use Quartz SiO₂ 99.5%+, 325 Mesh — provides defect-free silica network; eliminates carbonate and iron impurities that create glaze bubbles and rough texture.
- Use Washed Kaolin, low Fe₂O₃, 325 Mesh — gives the glaze slip correct suspension, prevents settling during application, and fires without causing discolouration or crawling.
- Verify LOI <0.5% on every raw material — organic matter and carbonates in any ingredient generate gas during firing that creates pinhole and blister defects in the finished glaze.
- Maintain NABL-certified COA per shipment on all three minerals — glaze quality is only as consistent as the most inconsistent raw material in the recipe.
Source: Aalok Overseas Technical Laboratory, Rajasthan, India · Manufacturer & Exporter of Feldspar, Quartz & Kaolin for Fine Glaze Production — 50+ Countries Since 1992 · www.feldsparindia.com
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Home › Blog › Fine Glaze in Ceramics Through Feldspar, Quartz & Kaolin
AALOK OVERSEAS INDIA · RAJASTHAN · MINERAL DIVISION · TECHNICAL BLOG
Glaze Flux · Silica Network · Suspension System · K-Feldspar · Na-Feldspar · Quartz 325M · Washed Kaolin · Low Fe₂O₃ · NABL COA · 50+ Countries · Exporter Since 1992
Published: July 2026 | Author: Aalok Overseas Technical Team | Category: Glaze Chemistry & Ceramic Raw Materials
REQUEST FREE GLAZE MINERAL SAMPLES → VIEW POTASH FELDSPAR VIEW KAOLINThe Three Minerals That Make a Fine Ceramic Glaze — Their Exact Roles
A ceramic glaze is not a single material — it is a precisely balanced system of three mineral categories, each performing an irreplaceable chemical and physical function during firing. No single mineral alone can produce a fine glaze. The quality of each ingredient — and the consistency of that quality from shipment to shipment — determines whether your fired glaze surface is smooth, glossy, and defect-free, or rough, dull, and full of pinholes.
MINERAL 01 — FLUX
Feldspar (K-Feldspar + Na-Feldspar)
Provides K₂O and Na₂O — the alkali fluxes that melt at 1000–1200°C and form the continuous glass phase. This glass phase is the glaze surface itself: it fills pores, smooths texture, creates gloss, and bonds glaze to body. Without sufficient, consistent feldspar flux, there is no smooth glaze — only a rough, semi-fused mat surface.
MINERAL 02 — GLASS NETWORK FORMER
Quartz Powder (SiO₂)
Provides the SiO₂ silica network that gives the glaze its hardness, chemical resistance, gloss depth, and thermal expansion behaviour. Quartz is the structural backbone of the glass phase — without correct SiO₂ content and fineness, the glaze is either too soft (scratches easily) or too stiff (crazes and cracks during cooling).
MINERAL 03 — SUSPENSION & PLASTICITY
Kaolin (China Clay)
Provides Al₂O₃ for glaze stability at temperature, and crucially — provides the colloidal clay particles that keep the glaze slip in suspension during storage and application. Without kaolin, glaze slips settle rapidly, leading to uneven application thickness, which causes crawling, bare patches, and surface irregularity in the fired glaze.
What Is a Fine Ceramic Glaze — and How Is It Measured?
A fine ceramic glaze is a fired glaze surface that meets the following measurable quality parameters simultaneously. If any one fails, the glaze is rejected at inspection.
| GLAZE QUALITY PARAMETER | MEASUREMENT / STANDARD | TARGET VALUE | PRIMARY MINERAL CONTROL |
|---|---|---|---|
| Surface Smoothness | Visual + tactile inspection; profilometer Ra value | Ra <0.5 μm (mirror glaze) | Feldspar fineness (325M) + Na-Feldspar flow |
| Gloss Level | Gloss meter — 60° angle | ≥85 GU (high gloss tile) | K₂O/Na₂O ratio in feldspar + SiO₂ from quartz |
| Whiteness / Colour | Spectrophotometer — GE / CIE whiteness | ≥88% GE (white wall tile) | Fe₂O₃ <0.06% in feldspar; TiO₂ <0.02% quartz |
| Pinhole / Blister Freedom | Visual count per m² — ISO 10545-2 | Zero visible defects (Grade A) | LOI <0.5%, Fe₂O₃ <0.06% in all raw materials |
| Glaze Adhesion (No Crawling) | Visual — bare clay patches after firing | Zero bare patches | Kaolin Al₂O₃ content + correct specific gravity of slip |
| Hardness / Scratch Resistance | Mohs scale / EN ISO 10545-6 | ≥5 Mohs (wall) / ≥6 (floor) | SiO₂ content and purity from quartz |
| Thermal Shock Resistance (No Crazing) | ISO 10545-9 — temperature cycling | No visible crazing | K₂O/SiO₂ expansion match — feldspar:quartz ratio |
8 Causes of Poor or Rough Ceramic Glaze — and the Raw Material Behind Each
CAUSE 01 — MOST COMMON
Insufficient Feldspar Flux — Incomplete Melt, Rough Matt Surface
When K₂O + Na₂O from feldspar is insufficient — either because the feldspar proportion in the recipe is too low, or because the K₂O/Na₂O of the supplied feldspar is below specification — the glass phase is incomplete. The result is a rough, semi-matt, porous glaze surface instead of a smooth gloss finish. Fix: Verify K₂O ≥11.5% in K-Feldspar, Na₂O ≥9.5% in Na-Feldspar, on every lot with NABL COA.
CAUSE 02 — FELDSPAR RELATED
Coarse Feldspar Particle Size — Unmolten Granules in Glaze Surface
Feldspar particles above 75 microns (coarser than 200 Mesh) do not melt completely within the fast-fire glaze cycle. These unmolten granules create localised rough spots, surface bumps, and matt patches surrounded by otherwise glossy glaze — one of the most common causes of glaze surface texture complaints. Fix: 325 Mesh feldspar, verified by wet sieve test on every lot.
CAUSE 03 — QUARTZ RELATED
Wrong Quartz Mesh or Low SiO₂ Purity — Glaze Too Stiff or Too Soft
Coarse quartz (above 100 microns) does not fully dissolve into the feldspar glass phase within the firing cycle — leaving residual crystalline silica patches that create a rough, granular glaze texture. Low-purity quartz (SiO₂ below 99%) introduces iron and titanium impurities that discolour and weaken the glass network. Fix: Quartz SiO₂ 99.5%+, 325 Mesh, Fe₂O₃ <0.02%.
CAUSE 04 — KAOLIN RELATED
Coarse or High-Iron Kaolin — Crawling and Discolouration
Kaolin with coarse particle size (above 2 microns D50) provides inadequate suspension — the glaze slip settles and separates during storage and application, causing uneven thickness. Thick zones crawl (shrink and retract) during firing; thin zones fire rough or pin-hole. High-Fe₂O₃ kaolin adds visible iron discolouration to the fired white glaze. Fix: Washed, low-Fe₂O₃ kaolin (<0.8%) with fine D50, 325 Mesh, NABL COA.
CAUSE 05 — GAS EVOLUTION
High LOI in Any Raw Material — Pinholes and Blisters in Glaze
Organic matter, carbonates, and water of crystallisation in any of the three minerals burn off during firing, releasing gas. If this gas evolution occurs after the glaze surface has begun to seal, it punches through — creating pinholes and blisters in the finished glaze. LOI must be below 0.5% in feldspar and quartz; kaolin naturally has higher LOI (up to 14%) from clay water, but this must be released in the bisque stage before glazing. Fix: LOI <0.5% in feldspar + quartz; ensure bisque is fully fired before glaze application.
CAUSE 06 — IRON CONTAMINATION
High Fe₂O₃ Across Any Mineral — Discolouration and Micro-Voids
Fe₂O₃ above 0.10% in feldspar, above 0.03% in quartz, or above 0.8% in kaolin introduces yellow-brown tints and generates gas micro-voids during firing — simultaneously reducing whiteness and creating surface defects. For fine white glaze, all three minerals must be specified and verified at low iron. Fix: Fe₂O₃ <0.06% (feldspar), <0.02% (quartz), <0.8% (kaolin) — NABL XRF COA per lot.
CAUSE 07 — SLIP PREPARATION
Incorrect Glaze Slip Specific Gravity — Over or Under Application
Even perfect raw materials fail if the glaze slip specific gravity is wrong. Too dense: glaze is applied too thick, causing crawling and glaze edge defects. Too thin: insufficient glaze coverage, rough fired surface, and pin-hole formation from bisque body gas escaping through a thin glaze layer. Consistent kaolin quality (fixed particle size, fixed water demand) is essential for maintaining stable slip specific gravity without constant adjustment. Fix: Use consistent, washed kaolin with verified plasticity index from NABL-COA supplier.
CAUSE 08 — BATCH INCONSISTENCY
Variable Raw Material Specifications Between Shipments
A glaze recipe tuned to K-Feldspar K₂O 12%, Quartz SiO₂ 99.5%, and Kaolin Al₂O₃ 36% will behave differently when supplied with K₂O 10.5%, SiO₂ 98%, or Al₂O₃ 33% in subsequent shipments — even from the same supplier if there is no per-lot COA verification. Batch inconsistency across all three minerals is the hardest-to-diagnose cause of erratic glaze quality. Fix: NABL COA on every lot of all three minerals; reject any lot outside ±0.3% of specification.
Glaze Defect Diagnostic — Symptom → Raw Material Cause → Fix
| GLAZE DEFECT OBSERVED | PROBABLE RAW MATERIAL CAUSE | RECOMMENDED FIX |
|---|---|---|
| Rough, matt surface — no gloss | Insufficient K₂O/Na₂O in feldspar; coarse feldspar PSD | Upgrade to 325M feldspar; verify K₂O ≥11.5% / Na₂O ≥9.5% by NABL COA |
| Pinholes — sharp craters in glaze | Fe₂O₃ too high in feldspar or quartz; high LOI | Fe₂O₃ <0.06% feldspar; SiO₂ 99.5%+ quartz; LOI <0.5% all minerals |
| Glaze crawling — bare clay patches | Coarse or inconsistent kaolin; high glaze shrinkage | Fine washed kaolin, correct specific gravity; check bisque dust/moisture |
| Cream / yellow tint in white glaze | Fe₂O₃ above 0.10% in feldspar or quartz | Premium K-Feldspar Fe₂O₃ <0.06%; Quartz Fe₂O₃ <0.02% |
| Glaze crazing — fine cracks after cooling | SiO₂ too low; feldspar:quartz ratio imbalanced | Increase quartz content; verify SiO₂ 99.5%+ at 325M; rebalance recipe |
| Blistering — dome-shaped bubbles in glaze | Organic matter or sulphates in feldspar; fast firing | LOI <0.5% + SO₃ <0.05% in feldspar COA; check bisque firing completeness |
| Glaze settles quickly in slip tank | Kaolin too coarse; insufficient colloidal fraction | Fine-particle washed kaolin with correct deflocculation; check kaolin D50 |
| Glaze quality varies batch-to-batch | No per-lot COA on feldspar, quartz, or kaolin | Demand NABL COA on every shipment of all three minerals; single-source supply |
Aalok Overseas — Three Minerals, One Fine Glaze Solution
Potassium Feldspar — The Glaze Flux
K-Feldspar K₂O 11.5–13%, Fe₂O₃ <0.06%, 325 Mesh delivers a clean, complete glass phase that creates surface gloss, whiteness, and pinhole-free smoothness. High K₂O provides a more viscous, harder glass — ideal for floor tile glazes and sanitaryware requiring durability. Consistent batch-to-batch K₂O (±0.3%) keeps glaze melt behaviour predictable every production run.
K₂O 11.5–13% · Fe₂O₃ <0.06% · 325M · GE Whiteness 90–93% · NABL COA
Sodium Feldspar — The Glaze Flow Agent
Na-Feldspar Na₂O 10–11%, 325 Mesh melts at a lower temperature and produces a less viscous glass — keeping the glaze surface fluid longer during firing. This extended fluidity enables the glaze to self-level, heal pinholes before they set, and produce a mirror-smooth surface in fast-fire kiln conditions. Essential for wall tile glazes and decorative finishes requiring maximum flow.
Na₂O 10.0–11.0% · Fe₂O₃ <0.12% · 325M · GE Whiteness 84–88% · NABL COA
Quartz Powder — The Glaze Structure
Quartz SiO₂ 99.5%+, 325 Mesh dissolves completely into the feldspar glass phase, extending the silica network for higher hardness, deeper gloss, and correct thermal expansion. High-purity quartz at 325 Mesh has no residual coarse particles that create rough spots — and no iron or titanium impurities that discolour the white glaze or generate gas defects.
SiO₂ 99.5%+ · Fe₂O₃ <0.02% · TiO₂ <0.02% · 325M · GE Whiteness 90–95% · NABL COA
Kaolin — The Glaze Suspension Agent
Aalok Overseas Kaolin (Al₂O₃ 34–38%, Fe₂O₃ <0.8%, 325 Mesh) provides fine clay platelets that keep the glaze slip in stable suspension — eliminating settling, separation, and uneven application thickness. Al₂O₃ from kaolin also raises the glaze's refractoriness, preventing glaze run-down on vertical surfaces in sanitaryware and tall insulators.
Al₂O₃ 34–38% · Fe₂O₃ <0.8% · SiO₂ 46–50% · 325M · Low Sand · NABL COA
Standard Glaze Recipe Reference — Using Aalok Overseas Minerals
| APPLICATION | K-FELDSPAR % | NA-FELDSPAR % | QUARTZ % | KAOLIN % | OTHER ADDITIONS | FIRING TEMP |
|---|---|---|---|---|---|---|
| High-Gloss Wall Tile Glaze | 35–40% | 15–20% | 20–25% | 10–15% | Calcite 5–8%, ZnO 2–3% | 1080–1120°C |
| Porcelain Floor Tile Glaze | 40–50% | 10–15% | 20–25% | 8–12% | Calcite 3–6%, BaCO₃ 1–2% | 1200–1250°C |
| Sanitaryware Glaze | 45–55% | 5–10% | 20–25% | 12–18% | ZnO 2–4%, Dolomite 2–3% | 1220–1260°C |
| Matt Tile Glaze | 25–35% | 10–15% | 15–20% | 15–20% | Al₂O₃ 5–8%, ZrO₂ 3–5% | 1080–1130°C |
| Fast-Fire Wall Tile | 25–30% | 20–25% | 20–25% | 10–12% | Frit 15–20%, Calcite 3–5% | 1050–1100°C |
Note: These are reference formulations. Adjust proportions based on your specific firing temperature, kiln type, and tile format. Request Aalok Overseas technical data sheets for application-specific glaze formulation support.
Aalok Overseas — Complete Specification Reference for Fine Glaze
| MINERAL | GRADE | KEY OXIDE | FE₂O₃ | LOI | GE WHITENESS | MESH | GLAZE ROLE |
|---|---|---|---|---|---|---|---|
| K-Feldspar | Standard 200M | K₂O 11.0–12.5% | <0.08% | <0.5% | 88–92% | ≥200M | Wall Tile · Domestic Glaze |
| K-Feldspar | Premium 325M |
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