ISO 3262 vs ASTM D605 on Talc

Choosing the right specification

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.