Importers often judge a shipment by its color—but once the sheets arrive, fading, rust spots or thickness over-spec can erase 5–12 % of your profit overnight. The rainbow top-coat is only the tip of the iceberg. Below are seven technical controls we run in our own mill audits; use them as a non-negotiable purchase-order checklist.
201 – Low-nickel, 16 % Cr. Acceptable for dry interior décor if humidity < 60 %.
304 – 18 % Cr / 8 % Ni. Default for kitchens, elevators, façades in non-coastal cities.
316L – 2–3 % Mo. Specify when chloride deposition > 0.5 mg/m²/day (within 5 km of shoreline or indoor pools).
Quick test: Ask the mill for ASTM A240 heat-analysis certificate—not just a 304 stamp on the edge. Molybdenum must read ≥ 2.0 % for real 316L.
| Finish | Ra (µm) | Color take-up | Typical use |
|---|---|---|---|
| 2B | 0.10–0.25 | Good | Hidden parts, budget jobs |
| BA | 0.02–0.05 | Excellent | Reflective wall cladding |
| No. 4 | 0.30–0.40 | Fair (directional) | Kitchen appliances |
| Hairline (HL) | 0.20–0.30 | Very good | Elevator cabins |
| Mirror #8 | < 0.02 | Best brilliance | Luxury columns |
Rule: The smoother the surface, the brighter the PVD hue—but also the more visible any handling scratch. Specify protective PVC film 50 µm on mirror sheets.
PVD (Ti, Cr, Zr nitrides/carbides) – 0.3–1.2 µm, hardness HV 1 800, lifetime fade ΔE < 1 after 10 yr QUV-B. Best for exterior.
Nano-ceramic clear – 5–15 µm, adds fingerprint resistance, moderate UV.
PET laminated – 60–120 µm, cheap, interior only; edges peel when laser-cut.
Powder coat on stainless – 60–80 µm, unlimited RAL, but hides metallic lustre.
PO wording: “Coating shall be PVD Ti-C-N under 10⁻³ mbar vacuum, target thickness 0.8 ± 0.2 µm, adhesion ≥ 5B per ASTM D3359.”
Salt-spray ASTM B117 1 000 h – no red rust > 5 % of surface.
QUV-B 313 nm 500 h @ 60 °C – color shift ΔE ≤ 1.0 vs baseline.
T-bend ASTM D4145 2T – no crack at 180° bend over same radius.
Impact ASTM D2794 20 in·lb – no coating loss.
Cross-hatch ISO 2409 1 mm grid – class 0 (no peel).
Ask for the original lab PDF—not a blurred WhatsApp forward. Reports older than 12 months are invalid if the mill changed chemical lots.
Example: 1.0 mm nominal sheet.
ASTM A480 wide tolerance: ±0.07 mm → actual 0.93–1.07 mm.
Half-standard: ±0.05 mm → 0.95–1.05 mm.
Mill special: ±0.02 mm → 0.98–1.02 mm.
Shipping by weight? A container holding 23 t of 1.0 mm ±0.07 mm may contain only 21.8 t of “usable” area if you design at 1.0 mm. Tightening to ±0.02 mm recovers that 5 % extra area—worth USD 1 850 on today’s 304 base price.
Surface: 50 µm white PVC film laser-safe.
Interleave: 80 g/m² neutral kraft paper.
Desiccant: 4 bags × 2 g non-woven per closed coil, 8 bags per sheet crate.
Crate: fumigation-free plywood, 0.8 mm steel strapping, corner angles.
Humidity card: should read < 40 % RH when container doors open.
Insist on seaworthy packing per ASTM D3951; otherwise you pay the re-polish bill in your own warehouse.
Heat number & grade on Mill Test Certificate matches packing list.
Coating type, target thickness and adhesion class written.
Salt-spray & QUV lab reports dated < 1 yr.
Thickness tolerance class stated (prefer ±0.02 mm).
Surface finish Ra value and roughness trace supplied.
Sheet dimensions, diagonal tolerance ≤ 1 mm.
Plastic film type and peel adhesion 5–8 N/25 mm.
Desiccant quantity & humidity indicator card enclosed.
Photos of packed bundles before container sealing.
Insurance covered for 110 % of CIF value.
Color sells, but specifications keep you profitable. Paste the seven points above into your next RFQ and watch quotations level-up—or watch suppliers disappear. Either way, you win.
Need an independent mill audit or PVD sampling? Contact our specification team—we answer in 24 h.
<!--!doctype-->
