ISO 3262 vs. ASTM D605 on Talc — choosing the right specification
1 What the two standards are
| Standard |
Latest revision |
Official title |
| ISO 3262 – Parts 10 & 11 |
2024 editions (iso.org, iso.org) |
Extenders — Specifications and methods of test – Part 10: Natural talc/chlorite in lamellar form |
**Part 11: Natural talc in lamellar form containing carbonates**
Global, but dominant in Europe, Middle East, SE-Asia
Decorative & industrial **paint** formulators, EU importers, REACH dossiers
|
ASTM D605-82 (reapproved 2019) | 2019 reaffirmation (
astm.org) |
Standard Specification for Magnesium Silicate Pigment (Talc) | North & Latin America; US federal and defence contracts | US paint makers, DoD coatings, NAFTA QC labs |
2 Scope and philosophy
- ISO 3262 treats talc as one member of a modular extender family.
Two parts cover talc:
- Part 10 — talc/chlorite blends (low carbonate)
- Part 11 — talc associated with carbonates
Both parts classify products by mineralogy, not by performance grade.
- ASTM D605 targets a single end-use: paint-pigment-quality talc.
No mineralogical sub-classes; a batch either meets the chemical & physical limits or it fails.
3 Key property requirements (abridged)
| Property |
ISO 3262-10/11 ranges* |
ASTM D605 limits* |
Notes |
| Chemical composition |
SiO₂ + MgO ≥ 88 % (pure talc) |
|
|
| CaO ≤ 2 % (Part 10) or ≤ 10 % (Part 11, carbonate talc) |
MgO + SiO₂ ≥ 90 %; |
|
|
| Fe₂O₃ ≤ 1.0 %; |
|
|
|
| CaO ≤ 2 % |
ASTM gives absolute maxima; ISO splits by class. |
|
|
| Matter volatile at 105 °C |
≤ 1.0 % |
≤ 1.0 % |
Same test (ISO 787-2 vs ASTM D280). |
| Residue on 45 µm sieve (325 mesh) |
Class-dependent, ≤ 0.05 % to 1 % |
≤ 0.5 % |
ISO allows coarser grades for textured paints. |
| Oil absorption (rub-out) |
≤ 30 g / 100 g |
≤ 30 g / 100 g |
Identical cap. |
| Whiteness / brightness |
Ry (CIE-Y) reported; no fixed min — user chooses |
Ry ≥ 80 (guide value) |
ISO supplies the test method; buyer sets the pass line. |
| pH (10 % slurry) |
8 – 10 |
7.5 – 9.5 |
Slightly different window. |
*Extracts only the talc-related clauses; both standards cite the detailed test methods (ISO 787 series vs ASTM D-series).
4 Differences that matter in commercial practice
| Topic |
ISO 3262 |
ASTM D605 |
| Classification label |
“ISO 3262-10 — Talc/chlorite, Class A” or “ISO 3262-11 — Talc-carbonate, Class B” |
Simply “ASTM D605 compliant” (no classes) |
| Mineralogy tolerance |
Explicit clauses for chlorite or carbonate admix |
Silent on chlorite; carbonate limited only by CaO max |
| Colour requirement |
Buyer-defined (standard gives test) |
Informative note: Ry ≥ 80 is typical |
| Regulatory cross-reference |
Links to EU chemicals legislation and ISO 16000 series for VOC testing |
Cited by US federal coatings specs (MIL-M-15173) (quicksearch.dla.mil) |
| Test-method backbone |
ISO 787 general methods (many labs outside US already accredited) |
ASTM pigment test series (D1200 viscosity, D281 oil absorption, etc.) |
| Units |
International System (g / 100 g, %) |
Same, but older printings carried inch-mesh in parentheses |
5 Choosing which standard to cite on your COA
| You are selling to… |
Safer reference |
| EU paint maker, Middle-East distributor, or any customer asking for “ISO spec” |
ISO 3262 (Part 10 or 11) |
| US / Canada coatings company, government or defence contract |
ASTM D605 |
| Plastic, cosmetic or pharmaceutical client |
Neither fits perfectly — instead list internal grade limits plus ISO/ASTM test methods separately |
A growing number of exporters print both declarations on one certificate to avoid re-testing.
6 Bridging the two when a buyer switches spec
- Map chemical limits
ISO’s talc-carbonate class can exceed ASTM’s CaO max; screen CaO first.
- Align fineness
ISO allows up to 1 % residue where ASTM caps at 0.5 %. Run a 325-mesh check if you move from ISO to ASTM markets.
- Re-state oil absorption & moisture (identical limits—no retest needed if methods match).
- Colour/brightness
ASTM gives only guidance; insert the actual Ry, L*, b* figures you already measure for ISO.
7 Key take-aways
- ISO 3262 is broader, mineralogy-based and common in Europe; ASTM D605 is a pass/fail paint-pigment spec preferred in North America.
- Core tests—fineness, volatiles, oil absorption—are almost identical; differences lie mainly in chemical maxima and grade naming.
- State both the standard and the edition year; property limits shift (ISO 2024 rev. tightened Fe₂O₃ and volatile matter).
- When exporting, verify CaO, Fe₂O₃ and 325-mesh residue first—these three parameters trip most cross-spec failures.
Armed with this comparison, you can label your talc correctly, negotiate specs with international buyers, and avoid surprise rejections at the QC bench.
