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Posted by Admin on April, 15, 2026
L* a* b* Colour Values
in Feldspar, Quartz & Industrial Minerals
What CIE L*a*b* means for whiteness, brightness and colour purity in feldspar, quartz, kaolin, mica and other industrial minerals — with reference charts, data tables, measurement instruments and how Aalok Overseas guarantees your grade.
Published by Aalok Overseas / FeldsparIndia.com · Rajasthan & Gujarat, India
Understanding Colour Science
What Are CIE L* a* b* Values?
The CIE L*a*b* colour space (also written CIELAB) is the international standard for quantifying colour, developed by the Commission Internationale de l'Éclairage (CIE) in 1976. It is the most widely used system in ceramics, paints, paper, plastics, and mineral industries for specifying whiteness, yellowness, and tint in powder products.
Unlike RGB (screen colours) or CMYK (print inks), L*a*b* is perceptually uniform — equal numerical differences correspond to roughly equal perceived colour differences regardless of hue. This makes it ideal for pass/fail QC specifications: "L* ≥ 90, a* ≤ 0.5, b* ≤ 3.0" is a precise, instrument-verifiable requirement.
0 = perfect black
100 = perfect white
Feldspar target: ≥88–95
+a* = reddish tint
−a* = greenish tint
Feldspar target: −1 to +1
+b* = yellowish tint
−b* = bluish tint
Feldspar target: +1 to +4
CIE L*a*b* COLOUR SPACE
+a*−a*−b*+b*L*0→100KaolinK-SparNa-SparQuartzMicaRawApproximate mineral positions in CIE a*b* plane (centre = white, L*→100)
L* LIGHTNESS SCALE — 0 (Black) to 100 (Perfect White)
Reference Data
CIE L*a*b* Reference Values — Industrial Minerals Comparison Chart
Values measured under D65 illuminant, 10° standard observer, on pressed powder pellet or packed cell. Actual values vary by deposit, processing, and Fe₂O₃ content. Values shown are typical export-grade ranges for India-origin minerals.
| Mineral | L* (Lightness) | a* (Red/Green) | b* (Yellow/Blue) | Whiteness WI | Fe₂O₃ Max | Key Industry Use |
|---|---|---|---|---|---|---|
| 🪨 Potash Feldspar — Standard | 86–90 | −0.5 to +0.8 | +2.0 to +4.5 | 70–78 | <0.15% | Tile body, floor tile |
| 🪨 Potash Feldspar — Premium | 90–94 | −0.3 to +0.5 | +1.0 to +3.0 | 78–85 | <0.10% | Glaze, porcelain body |
| 💎 Soda Feldspar (Albite) — Std | 88–92 | −0.5 to +0.6 | +1.5 to +3.5 | 75–83 | <0.10% | Ceramic glaze, sanitaryware |
| 💎 Soda Feldspar — Premium | 92–95 | −0.3 to +0.4 | +0.8 to +2.0 | 82–90 | <0.06% | Fine porcelain, bone china |
| 🔷 Quartz Powder (SiO₂ ≥99%) | 93–97 | −0.4 to +0.3 | −0.5 to +1.5 | 86–94 | <0.02% | Glass, coatings, electronics |
| 🪶 Kaolin (China Clay) — Washed | 90–96 | −0.8 to +0.2 | +0.5 to +2.0 | 82–92 | <0.60% | Paper coating, ceramics |
| ✨ Muscovite Mica — Ground | 72–82 | −1.0 to +1.5 | +3.0 to +7.0 | 55–68 | <3.0% | Paints, plastics, cosmetics |
| 🪨 Calcite / GCC — Precipitated | 95–98 | −0.5 to +0.2 | −1.0 to +1.5 | 90–96 | <0.10% | Paper filler, paints, plastics |
| 🪨 Talc — Cosmetic Grade | 88–96 | −0.6 to +0.3 | +0.5 to +3.5 | 78–88 | <0.50% | Cosmetics, rubber, ceramics |
| ⬜ Raw / Unbeneficiated Feldspar | 65–78 | +0.5 to +2.5 | +4.0 to +9.0 | 40–60 | >0.30% | Construction, filler (non-critical) |
Pictorial Chart
L* Value Comparison — Mineral Brightness Chart
Factors That Affect L*a*b*
What Drives L*a*b* Values in Feldspar & Quartz?
Fe₂O₃ — Iron Oxide
Primary driver of yellowing (+b*) and darkening (↓L*). Each 0.01% increase in Fe₂O₃ drops L* by ~0.3–0.8 points and raises b* by ~0.2–0.5 units. Even trace iron (0.05%) causes visible cream tint in white ceramics. Magnetic separation targets Fe₂O₃ <0.10% for premium grade.
TiO₂ — Titanium Oxide
Secondary yellowing agent. TiO₂ in feldspar >0.05% contributes strongly to +b* (yellowish hue). It is less reducible by magnetic separation than iron. High-TiO₂ feldspar is rejected for white-body porcelain even if Fe₂O₃ is low. Target: TiO₂ <0.02% for premium white ceramic bodies.
Particle Size / Fineness
Finer = brighter. Smaller particles scatter light more uniformly, increasing perceived whiteness. 325M feldspar consistently shows L* 2–4 points higher than 100M of the same deposit. This is why glaze-grade (325M) commands a premium: better L* AND better application performance.
Organic / Carbon Impurities
Darkens L* significantly; drives a* and b* irregularly. Carbon contamination from near-surface mining zones or organic-rich host rock reduces L* by 3–10 points. Removed by flotation or calcination. Fired feldspar (kiln pre-treated) eliminates organics completely.
Beneficiation Process
WHIMS / HIMS magnetic separation removes iron-bearing minerals (biotite, hornblende, ilmenite). Froth flotation removes mica and coloured silicates. Each beneficiation step adds 2–5 L* points. Aalok Overseas multi-stage magnetic separation achieves consistent Fe₂O₃ <0.10% and L* ≥90.
Moisture & Sample Prep
Wet powder reads lower L* than dry. ISO 787-1 requires drying at 105°C for 2 hrs before measurement. Sample cell packing pressure also affects results — loose powder gives lower L* than pressed pellet. All Aalok CoA measurements are on oven-dried, uniformly pressed powder pellets per ISO 11664.
Testing Methods
How L*a*b* Is Measured — Instruments, Standards & Methods
🔭 HOW A SPECTROPHOTOMETER MEASURES L*a*b* — PROCESS DIAGRAM
💡 LightSourceD65 / C / AilluminantIntegrating Sphered/8° or 0°/45° geometryPOWDERpelletPressed Sample📡 DetectorArray / DiffractionGrating 360–780nmReflectance curve⚙️ SoftwareCIE 1976 calculationXYZ → L*a*b*WI, YI, ΔE* output📄 CoAReportL* a* b*WI · YISTEP 1STEP 2STEP 3STEP 4STEP 5OUTPUT🔭 BENCHTOP SPECTROPHOTOMETER
The gold standard for mineral L*a*b* measurement. Integrating sphere geometry (d/8°) measures diffuse reflectance across full visible spectrum (360–780 nm). CIE calculation engine converts XYZ tristimulus to L*a*b*, whiteness index (ASTM E313 / CIE 2004), yellowness index (ASTM D1925).
Key Instruments:
Konica Minolta CM-3600A · HunterLab UltraScan PRO · Datacolor 800 · BYK-Gardner Color Guide · Hunterlab MiniScan EZ · Minolta CR-400 · Lovibond RT-Series
Standard: ISO 11664-4 · ASTM E308 · CIE 15
📱 PORTABLE / HANDHELD COLORIMETER
Fast QC on the production floor. Aperture placed directly on powder surface or pressed pellet. 3-filter colorimeter or compact diode array. Less accurate than benchtop but sufficient for pass/fail production QC (±0.5–1.0 L* units). Results transferable to benchtop via correlation factor.
Key Instruments:
Konica Minolta CR-10 · X-Rite ColorMite · HunterLab MiniScan EZ Plus · Tintometer Lovibond PFX series · PCE-TCR 200 · CHN-Spec CS-210
Standard: ISO 7724-1 · DIN 5033
🧪 SAMPLE PREPARATION
Critical for reproducibility. Powder must be dried (105°C, 2 hrs), then pressed into a uniform pellet using a hydraulic press and standard pellet die (10–40 mm diameter), or packed tightly into a black-backed cell. Sample thickness must exceed optical depth (~3 mm for feldspar). Measurement under identical illuminant and geometry every time.
Equipment Needed:
Lab oven (105°C) · Hydraulic pellet press (5–10 tons) · Stainless pellet die 40mm · Powder cell with black backing · Desiccator (measurement within 30 min of prep)
Standard: ISO 787-1 · ASTM E1347
📊 WHITENESS & YELLOWNESS INDICES
WI and YI are single-number summaries derived from L*a*b*. Whiteness Index (WI) per ASTM E313: WI = Y + 800(x₀ − x) + 1700(y₀ − y). Higher WI = whiter. Yellowness Index (YI) per ASTM D1925: YI = 100(1.28X − 1.07Z)/Y. Positive YI = yellow cast, target: YI <4 for ceramic-grade feldspar.
K-Spar Std
WI 70–78
Na-Spar Prem
WI 82–90
Quartz
WI 86–94
Colour Difference
ΔE* — Colour Difference & Batch-to-Batch Consistency
ΔE* (Delta E) is the total colour difference between two samples in L*a*b* space: ΔE* = √(ΔL*² + Δa*² + Δb*²). It is the most important QC metric for mineral supply chains because it quantifies batch-to-batch consistency.
| ΔE* Value | Human Perception | Industry Verdict |
|---|---|---|
| < 1.0 | Imperceptible | ✅ PASS — Excellent consistency |
| 1.0 – 2.0 | Barely noticeable by expert | ✅ PASS — Acceptable for most uses |
| 2.0 – 3.5 | Noticeable on close inspection | ⚠️ MARGINAL — Review specification |
| 3.5 – 5.0 | Clearly visible at a glance | ❌ FAIL — Reject or downgrade batch |
| > 5.0 | Obvious, different colour | ❌ REJECT — Major quality deviation |
Batch-to-batch ΔE* <1.5 for all export-grade feldspar and quartz. Every container shipment accompanied by a CoA with L*, a*, b*, WI, YI values. Reference standard samples retained for 24 months for dispute comparison.
ΔE* SCALE VISUALISED
REFΔE <1ΔE 1–2ΔE 2–3.5ΔE 3.5–5ΔE >5Batch ABatch BWhite dot = reference standard. Coloured dots = batch samples. Target: within inner green circle.
Our Products
L*a*b* Certified Feldspar & Quartz — Guaranteed Whiteness from India
Every shipment from Aalok Overseas is accompanied by a full CoA that includes L*, a*, b*, Whiteness Index (ASTM E313), Yellowness Index (ASTM D1925), measured on a calibrated benchtop spectrophotometer on oven-dried pressed pellets. No guesswork — every number is verifiable.
⭐ Why L*a*b* Buyers Choose Aalok Overseas / FeldsparIndia.com
🎨 L*a*b* CoA Every Shipment
Full spectrophotometric values: L*, a*, b*, WI (ASTM E313), YI (ASTM D1925) on oven-dried pressed pellets
🔬 Batch-to-Batch ΔE* <1.5
Consistent whiteness across all containers. Reference standards retained 24 months for dispute resolution
🧲 Multi-Stage Magnetic Separation
WHIMS + LIMS beneficiation achieves Fe₂O₃ <0.10%, directly lifting L* by 4–6 points vs raw ore
🏅 SGS / Bureau Veritas Option
Third-party pre-shipment inspection including L*a*b* verification available on request
📦 Free Sample with Full CoA
500g–2kg sample with complete spectrophotometric report dispatched worldwide in 48 hours
🌍 50+ Countries Supplied
Vietnam, Indonesia, Bangladesh, UAE, Malaysia, Sri Lanka, Nepal and 40+ more — AIFTA / SAFTA CoO available
Get in Touch
Contact Aalok Overseas — L*a*b* Certified Feldspar & Quartz from India
👩💼 Export Director
Ms. Ankita Agrawal
Director — Exports & International Relations
📍 Origin & Ports
Rajasthan & Gujarat, India
Mundra · Kandla · JNPT · Chennai
📦 Free Sample — Any Grade — with Full L*a*b* Spectrophotometric CoA — 48 Hours Worldwide
Specify: mineral (Potash / Soda Feldspar / Quartz) + mesh size + required L* minimum. Email exports@aalokoverseas.com or WhatsApp +91-9004229525. Full XRF oxide CoA + L*a*b* spectrophotometric report with every sample. No charge to qualified industrial buyers.
Aalok Overseas / FeldsparIndia.com — L*a*b* Certified Feldspar, Quartz & Industrial Minerals from India
Potassium Feldspar · Sodium Feldspar (Albite) · Quartz Powder · Kaolin · Muscovite Mica · Silica Sand
SEO: feldspar L value · feldspar whiteness index · quartz LAB value · kaolin L a b colour · CIE Lab minerals · spectrophotometer mineral · feldspar brightness · whiteness feldspar ceramics · L* a* b* colour measurement · WI YI feldspar · Delta E mineral · feldspar colour certification · FeldsparIndia.com · Aalok Overseas · CIELAB ceramics minerals India
www.feldsparindia.com | www.aalokoverseas.com | exports@aalokoverseas.com | +91-9004229525
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