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Posted by Admin on July, 16, 2026
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What Is LOI in Feldspar — and Why Does It Matter for Ceramic Production?
Why LOI matters — 5 practical effects on ceramic production:
- Gas release timing — LOI components burn off or decompose during firing, and inconsistent LOI shifts when this gas release happens relative to the body's densification, risking trapped gas defects.
- Shrinkage predictability — variable LOI adds an unpredictable component to firing shrinkage, making dimensional tolerance harder to hold batch after batch.
- Surface defects — high LOI is a common contributor to pinholing, blistering, and micro-bubbling in glaze and glass surfaces.
- Paid weight, not product — LOI is weight that burns away during firing, meaning buyers are effectively paying freight and material cost for mass that never becomes part of the finished product.
- A leading indicator of purity — LOI outside a mineral's normal expected range can signal contamination or an unexpected mineral mix, making it a useful quality check beyond its direct firing impact.
Source: Aalok Overseas Technical Laboratory, Rajasthan, India · Manufacturer & Exporter of Low-LOI Feldspar, Quartz & Kaolin to 50+ Countries Since 1992 · www.feldsparindia.com
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AALOK OVERSEAS INDIA · RAJASTHAN · FELDSPAR DIVISION · TECHNICAL BLOG #18
Loss on Ignition · Gas-Release Defects · Firing Shrinkage Control · Low-LOI Feldspar, Quartz & Kaolin · NABL COA · Exporter Since 1992
Published: July 2026 | Author: Aalok Overseas Technical Team | Category: Ceramic Raw Material Quality
REQUEST LOW-LOI FELDSPAR SAMPLE → VIEW FELDSPAR SPECIFICATIONSWhat Is LOI (Loss on Ignition) — and How Is It Measured?
Loss on Ignition (LOI) is a standard laboratory test that measures the percentage weight loss of a mineral sample after it is heated to a fixed high temperature — typically 950-1000°C — for a set period, usually until weight stabilises. The weight lost represents volatile components: physically bound (adsorbed) water, chemically bound (crystal-structure) water, carbonates that decompose to release CO₂, sulphides and sulphates, and any organic matter. In feldspar, LOI is generally low since feldspar's crystal structure holds little bound water compared to clay minerals — but even a small LOI variation matters because feldspar is used in precisely controlled proportions within a ceramic body recipe.
Typical LOI Ranges by Mineral and Application
| MINERAL | TYPICAL LOI RANGE | WHY IT DIFFERS |
|---|---|---|
| Potassium Feldspar (Premium Grade) | <0.35-0.6% | Low bound water in crystal structure; mainly trace carbonate/organic |
| Sodium Feldspar (Premium Grade) | <0.35-0.6% | Similar crystal structure to potash feldspar |
| Quartz Powder (Premium Grade) | <0.1-0.25% | Crystalline silica holds minimal bound water or volatiles |
| Kaolin | 12-14% (normal, not a defect) | Kaolinite's crystal structure contains chemically bound hydroxyl water, released on dehydroxylation during firing |
Kaolin's high LOI is expected and is not itself a quality problem — what matters for kaolin is that LOI stays consistent within its normal band, since an LOI reading well outside 12-14% can indicate contamination.
8 Reasons LOI Matters for Ceramic Production
REASON 01 — MOST DIRECT IMPACT
Gas Release Timing During Firing
As LOI components burn off or decompose, they release gas — water vapour, CO₂, and other volatiles — at specific temperature points during the firing cycle. If this gas release happens after the body has begun to seal and densify (particularly once the glaze surface starts to mature), the trapped gas cannot escape cleanly and shows up as pinholes, blisters, or bubbles.
REASON 02 — DIMENSIONAL CONTROL
Firing Shrinkage Predictability
Densification and shrinkage are affected by how much mass a body loses during firing and when. Variable LOI in the feldspar or quartz component adds an unpredictable variable to total shrinkage, on top of the flux-driven vitrification shrinkage that a body is designed around — making dimensional tolerance harder to hold consistently.
REASON 03 — COST, NOT JUST QUALITY
LOI Is Paid Weight That Never Becomes Product
Every tonne of feldspar shipped and invoiced includes its LOI weight — material that burns away during firing and never contributes to the final fired body. A feldspar with 1.0% LOI versus 0.4% LOI means paying for, transporting, and processing extra dead weight that adds no value to the finished product.
REASON 04 — PURITY INDICATOR
LOI as an Early Warning for Contamination
A feldspar or quartz lot with LOI unexpectedly higher than its normal range can indicate contamination with clay, organic matter, or carbonate minerals picked up during mining or handling — making LOI testing a useful proxy check even before full XRF chemistry results are available.
REASON 05 — GLAZE SURFACE QUALITY
Gas Release Directly Affects Glaze Gloss and Clarity
In glaze and frit applications, gas escaping through a maturing glaze layer is one of the most common causes of reduced gloss, dullness, or visible bubble defects on the fired surface — particularly relevant for premium, high-whiteness, and clear-glaze products where surface perfection is inspected closely.
REASON 06 — BATCH-TO-BATCH CONSISTENCY
Kiln Schedules Are Tuned to a Specific LOI Assumption
Once a firing curve is optimised for a body's expected LOI and gas-release behaviour, switching to a raw material batch with materially different LOI — even without changing anything else — can shift defect rates without any obvious process change to point to.
REASON 07 — QUARTZ-SPECIFIC IMPACT
LOI Interacts with Quartz Inversion Behaviour
Quartz undergoes a crystalline phase inversion at 573°C with an associated volume change. Elevated LOI in the quartz component can compound the stress of this inversion with additional gas-release stress at a similar stage of firing, increasing the risk of dunting cracks in bodies already sensitive to thermal shock.
REASON 08 — DOCUMENTATION DISCIPLINE
LOI Should Be a Standard Line Item on Every COA
LOI is inexpensive and quick to test compared to full XRF chemistry, yet is sometimes omitted from supplier COAs. Its presence on every shipment's certificate is a simple, verifiable signal of a supplier's overall quality control discipline.
LOI-Related Firing Problem — Symptom → Cause → Fix
| SYMPTOM OBSERVED | PROBABLE CAUSE | RECOMMENDED FIX |
|---|---|---|
| Pinholing or blistering in fired glaze | High LOI causing gas release after glaze surface has begun to mature | Specify LOI <0.4-0.6% in feldspar/quartz COA; verify per shipment |
| Sizing/shrinkage drift with no other process change | Batch-to-batch LOI variation adding unpredictable shrinkage component | Demand consistent, verified LOI on every lot, not just an initial sample |
| Reduced glaze gloss or dull, hazy surface | Gas escaping through a maturing glaze layer during firing | Switch to low-LOI feldspar and quartz grades for glaze-critical applications |
| Dunting cracks correlating with a specific raw material lot | Elevated LOI compounding quartz inversion stress at 573°C | Verify LOI <0.15-0.25% in quartz component specifically |
| Unexplained defect rate increase after switching supplier | New lot's LOI materially different from the value the kiln schedule was tuned for | Request LOI match to previous supplier's typical value before switching |
| Supplier COA missing LOI entirely | Supplier not testing or reporting LOI as standard practice | Require LOI as a mandatory line item on every COA going forward |
Benefits & Advantages of Aalok Overseas Low-LOI Feldspar, Quartz & Kaolin
Consistently Low LOI Across the Product Range
Potash and soda feldspar held below 0.35-0.6% LOI, and quartz powder below 0.1-0.25% LOI, depending on grade — giving buyers predictable gas-release behaviour and firing shrinkage batch after batch.
Mine-Direct Control from Extraction to Export
Aalok Overseas controls extraction, washing, beneficiation, milling, and mesh grading in-house from its own Rajasthan operations, rather than reselling third-party material — the operational depth that keeps LOI, along with chemistry and mesh, within a tight band lot after lot.
LOI Reported on Every NABL-Accredited COA
Every shipment — not just an initial sample — is accompanied by a NABL-accredited Certificate of Analysis that includes LOI alongside full XRF chemistry, so buyers can verify consistency shipment to shipment rather than relying on one-time test data.
Grade Range Matched to LOI-Sensitive Applications
From standard grades for general wall tile production to premium and high whiteness grades for glaze, frit, and glass work where gas-release defects are most visible, Aalok Overseas' range lets buyers match LOI sensitivity to their specific application without switching suppliers.
Three Decades of Batch Consistency Experience
Aalok Overseas has manufactured and exported feldspar, quartz, and kaolin since 1992, building the process discipline and mine-zone selection experience needed to keep LOI — and the shrinkage and surface-quality outcomes tied to it — stable across large, continuous production runs.
Full Documentation Package with Every Shipment
NABL-accredited COA (including LOI), MSDS, Certificate of Origin, and packing documentation accompany every shipment, supporting both quality verification and smooth customs clearance at destination.
Aalok Overseas — LOI Reference by Product Grade
| PRODUCT | GRADE | LOI | APPLICATION |
|---|---|---|---|
| Potassium Feldspar | Standard 200M | <0.6% | Wall Tile · Domestic |
| Potassium Feldspar | Premium 325M | <0.4% | Porcelain · Export · Frit |
| Potassium Feldspar | Ultra White | <0.35% | Sanitaryware · Bone China |
| Sodium Feldspar | Standard 200M | <0.6% | Wall Tile · Glaze |
| Sodium Feldspar | High-Flow 325M | <0.4% | Fast-Fire Glaze · Frit |
| Quartz Powder | Standard 200M | <0.25% | Tile Body · Foundry |
| Quartz Powder | Premium 325M | <0.2% | Porcelain · Sanitaryware |
| Quartz Powder | Glass Grade | <0.15% | Container & Sheet Glass |
| Kaolin | All grades | 12-14% (normal) | Whiteware · Paper · Paint |
All grades: NABL XRF COA including LOI · MSDS · Certificate of Origin · Free sample — 48hr dispatch · FOB Mundra / Kandla · Export to 50+ countries
FAQ — LOI in Feldspar
Q
What does LOI stand for in feldspar testing?
LOI stands for Loss on Ignition — the percentage of a mineral sample's weight lost when heated to a standard high temperature, typically 950-1000°C, representing bound water, carbonates, sulphides, and organic matter that burn off or decompose.
Q
What is a good LOI value for feldspar?
Premium-grade potassium and sodium feldspar typically holds LOI below 0.35-0.6%. For glaze-critical, frit, or glass applications where gas-release defects matter most, LOI below 0.4% is generally preferred.
Q
Why does kaolin have much higher LOI than feldspar?
Kaolin's kaolinite crystal structure contains chemically bound hydroxyl water that is released only at higher firing temperatures during dehydroxylation, typically giving kaolin an LOI of 12-14%. This is normal and expected — what matters is that it stays consistent within that range, not that it matches feldspar's much lower LOI.
Q
Can high LOI cause cracks or defects in ceramics?
Yes. High or inconsistent LOI can cause pinholing, blistering, and reduced glaze gloss from gas release during firing, and can compound quartz's 573°C inversion stress to increase dunting crack risk in bodies already sensitive to thermal shock.
Q
How is LOI tested in a laboratory?
A dried sample of known weight is heated in a furnace to a standard temperature, typically 950-1000°C, until weight stabilises. The percentage weight lost during this process is reported as LOI, and is a standard line item on a full XRF Certificate of Analysis.
Q
Does Aalok Overseas report LOI on every shipment?
Yes. Every Aalok Overseas shipment is accompanied by a NABL-accredited Certificate of Analysis that includes LOI alongside full XRF chemistry (K₂O/Na₂O, Fe₂O₃, TiO₂, SiO₂), verified per shipment rather than on a one-time sample basis.
Search Keywords — 8 Languages
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REQUEST LOW-LOI FELDSPAR SAMPLE · NABL COA · LOI & FULL CHEMISTRY REFERENCE DATA
Contact Aalok Overseas — India's Low-LOI Feldspar, Quartz & Kaolin Specialist
Request free samples of low-LOI potassium feldspar, sodium feldspar, or quartz powder — with NABL-certified COA including LOI, full XRF chemistry, and MSDS. Consistent firing performance from the first batch, mine-direct sourced from Rajasthan since 1992.
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