ISO 3549 and ASTM D520 are the two standards procurement teams cite most often when buying zinc dust. They overlap in intent but diverge in details. And the divergence matters when you are writing tender language or auditing a CoA.
ISO 3549. The international standard
ISO 3549 specifies pigment grade zinc dust for paints, defines chemical limits (Total Zn, Metallic Zn, Pb, Cd, Fe, As, Cl, acid-insoluble) and physical properties (sieve residue, color). All Atso Tek grades are tested per ISO 3549.
ASTM D520. The North American standard
ASTM D520 covers zinc dust pigment for paint use, defines three types (I, II, III) by particle size and bulk density. Many North American specs reference D520 directly; many CoAs from European suppliers do not list it because the chemical limits are similar enough that ISO 3549 is taken as equivalent.
Practical implications
European, MENA and most Asian buyers. ISO 3549 is the working standard.
North American buyers, especially in the architectural and automotive coatings supply chain. ASTM D520 may be specified by name in the contract.
If your tender requires both, ask your supplier to test against both. The methods overlap enough that re-testing is usually inexpensive.
