Surface guide
QR codes on engraved and etched metal
Metal marking is the hardest QR surface because contrast comes from surface texture rather than colour, and the finish reflects. Use error correction H, keep modules at 0.5 mm or larger, and specify a matt or annealed mark rather than a polished cut.
| Typical scan distance | 15–40 cm |
|---|---|
| Minimum code width | 1.5–4 cm |
| Error correction | H |
Contrast comes from texture, not colour
There is no ink. The decoder sees a difference between a diffuse marked area and a specular unmarked one — and that difference depends entirely on the angle of the light and the camera. This is why a metal code that reads perfectly on the bench fails in the workshop.
Laser annealing on stainless steel produces a dark oxide with genuinely different luminance and is the most reliable method. Deep engraving relies on shadow and is the least reliable. Chemical etching and electrolytic marking sit in between.
Specification
- Modules at 0.5 mm or larger; below that the mark edges dominate.
- Error correction H — 30% damage tolerance covers scratches, oil and partial glare.
- Mark the code dark on a light substrate, not the reverse. Inverted metal codes fail more often.
- Bead-blast or brush the surrounding area so the unmarked modules are diffuse rather than mirror-finish.
Reading it
Phone cameras struggle. Direct Part Marking is normally read with a dedicated imager providing diffuse dome illumination. If a phone must read it, test with the actual finish under the actual lighting before committing to a production run.
Standards
For industrial traceability, the relevant grading standard is ISO/IEC 29158 (AIM DPM), which scores marks on cell contrast, modulation and reflectance uniformity — worth requesting from your marking supplier.