Gloss & Sheen Measurement Terms
Gloss and sheen values are how buyers specify matting performance, and misreading them costs money in reformulation. Gloss is measured in Gloss Units (GU) at 60° incidence per ASTM D523; values below 10 GU qualify as deep-matt, 10–35 GU as semi-matt, and above 70 GU as high-gloss. Sheen (measured at 85°) captures residual surface reflectance that 60° readings miss — a film at 5 GU/60° can still show 15–25 GU sheen, creating visible haze. Haze itself is the difference between 20° and 60° gloss readings, critical for automotive clearcoats. DOI (distinctness of image) measures reflection sharpness rather than intensity. Formulators comparing suppliers should always request both 60° and 85° values — a single 60° number hides sheen problems.
- Gloss Unit (GU) — Dimensionless reflectance value at a specified angle; 60° is the universal standard for matting agent evaluation.
- Sheen — Low-angle (85°) reflectance; the most common source of customer complaints on matt finishes.
- Haze — Milky appearance from micro-roughness; quantified as 20° minus 60° gloss differential.
- DOI (Distinctness of Image) — Reflection clarity metric; relevant for automotive and high-end industrial coatings, not typically a matting KPI.
Particle Size & Distribution Terms
Particle size distribution (PSD) is the single biggest lever controlling matting efficiency — get this wrong and no loading level fixes it. D50 is the median particle diameter in microns; commercial matting silicas range from 3 µm (ultra-fine, low efficiency, smooth feel) to 15 µm (coarse, high efficiency, rough texture). D90/D10 ratio (span) indicates distribution width; narrow-span grades (ratio < 3.0) give more predictable gloss. Top-cut (D98) matters for thin-film applications — particles exceeding dry film thickness (DFT) protrude and cause defects. A matting agent with D50 of 5 µm but D98 of 20 µm will ruin a 25 µm clearcoat. Always cross-check D98 against your target DFT.
- D50 (Median Particle Size) — The diameter where 50% of particles are smaller; the primary spec for matting agent grade selection. See our particle-size-vs-matting-efficiency guide for optimization data.
- PSD (Particle Size Distribution) — Full volume-weighted size curve; measured by laser diffraction (ISO 13320). Narrow PSD = more consistent batch-to-batch gloss.
- Top-Cut (D98) — The diameter below which 98% of particles fall; must stay under target DFT to avoid surface defects.
- BET Surface Area — Nitrogen adsorption measurement (m²/g) of total silica surface; higher BET (200–400 m²/g for fumed grades) increases resin demand and viscosity.
Silica Chemistry & Processing Terms
Understanding how matting silicas are made explains why they perform — and price — differently. Precipitated silica is produced by reacting sodium silicate with sulfuric acid, yielding porous particles with pore volumes of 0.5–1.8 mL/g; higher porosity means more resin absorption and stronger matting at lower loadings. Fumed silica is made by flame hydrolysis of SiCl₄ at >1000 °C, producing non-porous primary particles (7–40 nm) that aggregate into chains; it matts via surface roughness, not porosity. Sintering is controlled heat treatment (600–1000 °C) that partially collapses pore structure, reducing resin demand while sacrificing some matting power. Surface treatment with waxes or silanes (C8–C18 organosilanes) improves dispersibility, reduces viscosity build, and prevents moisture uptake during storage.
- Pore Volume — mL/g of internal void space in precipitated silica; directly correlates with matting efficiency and resin demand. Range: 0.5 mL/g (sintered) to 1.8 mL/g (high-porosity).
- Sintering — Thermal treatment that reduces pore volume and BET surface area; trades matting efficiency for easier dispersion and lower viscosity impact.
- Surface Treatment — Wax or organosilane coating applied to raw silica; wax-treated grades (3–6% wax) are the market standard for solventborne systems.
- Gel Silica — Silica gel produced by acidification of sodium silicate under controlled pH; offers intermediate porosity (0.4–1.0 mL/g) between precipitated and fumed grades.
Formulation & Application Terms
These are the terms you will encounter when integrating matting agents into real coating systems. Loading level is the weight percentage of matting agent on total formulation (typically 1–8% for precipitated, 0.3–2% for fumed); excessive loading kills film clarity and increases cost. Oxygen inhibition occurs in UV-cure systems where surface O₂ prevents full crosslinking, leaving a tacky surface layer — matting agents protrude through this uncured layer and scatter more light, so UV-matt coatings often appear 5–10 GU lower than oven-cured equivalents. Let-down shock is the viscosity spike when concentrate meets the let-down resin; wax-treated grades and proper pre-dispersion minimize this. Rub-out describes gloss change when rubbing a dried matt surface; poor rub-out resistance (>5 GU shift) indicates insufficient binder around silica particles.
- Loading Level — Matting agent dosage as wt% of total formula; the primary cost lever — a 1% reduction at $4/kg silica saves ~$40/ton of coating.
- Oxygen Inhibition — Surface cure interference by atmospheric O₂ in UV coatings; increases apparent matting but compromises film hardness and chemical resistance.
- Let-Down Shock — Sudden viscosity increase during thinning; caused by uncontrolled silica flocculation. Preventable with staged addition or pre-dispersed pastes.
- Rub-Out Resistance — Gloss stability after mechanical abrasion; measured as ΔGU at 60° after 10–20 rub cycles. Values >5 GU indicate formulation weakness.
Key Test Standards
Standardized testing is what separates spec sheets from guesswork. Every matting agent evaluation should reference these methods to ensure supplier comparisons are apples-to-apples. Gloss measurement follows ASTM D523 (or ISO 2813). Particle sizing uses laser diffraction per ISO 13320. Surface area is determined by BET nitrogen adsorption (ISO 9277). Pore volume and pore size distribution are measured by mercury intrusion porosimetry (ISO 15901-1) or nitrogen desorption (BJH method). Film thickness — critical for matching D98 to DFT — follows ISO 2808.
- ASTM D523 / ISO 2813 — Specular gloss measurement at 20°, 60°, and 85° angles; 60° is the primary angle for matting evaluation.
- ISO 13320 — Laser diffraction particle sizing; the standard method for reporting D50, D90, D98 values on silica TDS documents.
- ISO 9277 (BET) — Surface area by nitrogen gas adsorption; a key spec for comparing fumed vs. precipitated grades.
- ISO 2808 — Dry film thickness measurement; used to verify that matting agent top-cut does not exceed DFT.
Quick-Reference: Matting Agent Types at a Glance
This comparison covers the four main silica families buyers encounter in the market. Pricing reflects Q1 2026 China ex-works levels for reference — actual quotes vary by volume and surface treatment. For detailed performance comparisons, see our technical resources hub.
| Type | D50 (µm) | Pore Vol. (mL/g) | BET (m²/g) | Typical Loading | Price Tier |
|---|---|---|---|---|---|
| Precipitated (untreated) | 5–12 | 1.0–1.8 | 200–350 | 2–6% | $1,800–2,500/t |
| Precipitated (wax-treated) | 5–12 | 0.8–1.5 | 180–300 | 2–5% | $2,200–3,200/t |
| Gel Silica | 4–10 | 0.4–1.0 | 250–400 | 3–8% | $2,500–3,500/t |
| Fumed Silica | —* | Non-porous | 150–380 | 0.3–2% | $8,000–15,000/t |
| *Fumed aggregates 100–500 nm; D50 not applicable in conventional sense |
Frequently Asked Questions
Common questions about resources.
+What is a matting agent in coatings?
A matting agent is a finely divided additive — usually silica — that reduces surface gloss by creating controlled micro-roughness on the dried film. Precipitated silica is the most common type, used at 2–6 wt% loading to achieve 60° gloss values from 5 to 35 GU depending on particle size and pore volume.
+What particle size is best for matting agents?
D50 of 5–8 µm offers the best balance of matting efficiency and surface smoothness for most industrial coatings. Coarser grades (10–15 µm) deliver deeper matt at lower loadings but increase surface roughness. Always verify D98 stays below your target dry film thickness to avoid protrusion defects.
+What is the difference between precipitated and fumed silica matting agents?
Precipitated silica matts through internal porosity that absorbs resin and disrupts surface leveling, while fumed silica matts through surface roughness from nano-scale aggregates. Precipitated grades cost $2–3k/t and load at 2–6%; fumed grades cost $8–15k/t but load at only 0.3–2%. Most industrial matt coatings use precipitated silica for cost efficiency.
+Why does my matt coating show sheen at low angles?
Sheen appears because 60° gloss measurement misses residual reflectance visible at 85°. The usual cause is matting agent D50 that is too fine (under 4 µm) or insufficient loading. Switching to a coarser grade or increasing dosage by 0.5–1% typically eliminates visible sheen. See our gloss-measurement-fundamentals page for testing protocols.
+What does sintering do to a matting agent?
Sintering heats raw precipitated silica to 600–1000 °C, partially collapsing its pore structure. This reduces BET surface area by 30–50% and pore volume by 20–40%, which lowers resin demand and viscosity build. The trade-off is reduced matting efficiency — sintered grades typically need 1–2% higher loading to match unsintered equivalents.
+How does oxygen inhibition affect matting in UV coatings?
Atmospheric oxygen prevents full surface crosslinking in UV-cure systems, leaving a soft top layer that matting agent particles protrude through more easily. This gives 5–10 GU lower gloss readings than equivalent thermal-cure films. While visually effective, the uncured surface layer reduces hardness and chemical resistance — nitrogen inerting or wax-addition strategies can control the effect.
+What loading level of matting agent should I use?
Start at 3% for precipitated silica targeting 20–30 GU at 60°, then adjust in 0.5% increments. Deep matt (under 10 GU) typically requires 5–7%. Fumed silica loads are much lower — 0.5–1.5% for equivalent matting. Over-loading wastes material, increases viscosity, and reduces film transparency. Always optimize against your specific resin system.
+How do I compare matting agent suppliers fairly?
Request D50, D98, pore volume, and BET surface area on every technical data sheet — these four specs predict 80% of performance. Test at identical loading levels in your actual resin system, not in a reference lacquer. Measure both 60° and 85° gloss to catch sheen differences. Our particle-size-vs-matting-efficiency comparison provides benchmark data across major suppliers.
When evaluating matting agents, three numbers tell you 80% of what matters: D50 for efficiency, pore volume for resin demand, and D98 vs. your DFT for defect risk. Request all three from every supplier before running trials.