QR codes on metal: marking processes that scan

Metal gives a QR code decades of life but contrast is the battle: raw engraving is grey-on-grey until you add paint infill or an oxide layer. Laser annealing marks stainless steel black without cutting, photo-anodising seals dye under aluminium oxide, and brushed finishes scan better than polished because they scatter glare.

The metal problem: geometry is not contrast

A decoder needs a luminance difference of at least 40% between dark and light modules: see contrast ratio. Cutting a pattern into metal changes the surface's shape, not its colour: a plain engraved code is silver-grey recesses in a silver-grey face, visible to your eye mainly through shadows that move with the light. A camera at an arbitrary angle often sees almost no difference. Every successful metal QR process is really a way of manufacturing contrast.

Process options, compared

Process	How contrast happens	Durability	Notes
Laser annealing (stainless, titanium)	Heat grows a black oxide layer, no material removed	Decades; surface stays smooth	The standard for stainless asset tags and medical items
Engraving + paint infill	Recess filled with black (or white) enamel/epoxy	Decades; infill outlives surface print	The hybrid that wins outdoors: see etched vs printed
Photo-anodised aluminium	Dye image sealed under the anodic oxide layer	10–20 years outdoors	Print-quality detail; the mark is inside the surface
Deep engraving, no infill	Shadow only	Geometry lasts decades	Scans unreliably, angle- and light-dependent
UV flatbed / screen print on metal	Ink on the surface	Years, not decades	Fine indoors; abrasion and UV take it first

Polarity matters: annealing and infill produce dark modules on light metal, correct orientation. If a process yields light marks on a dark ground (laser-etched black anodised aluminium exposes bright metal), you have an inverted code; either invert the artwork so the final result reads dark-on-light, or accept reduced scan reliability (see colour inversion and polarity).

Glare: brushed beats polished

Metal is reflective, and glare behaves worse here than on gloss paper. A polished or mirror finish reflects the phone's flash straight back into the lens; a brushed finish scatters the reflection into a line; a bead-blasted matt finish scatters it fully. Rank for scanning: bead-blasted > brushed > polished. If the design demands polished metal, tilt the mounting 15–30° and oversize the code so a hotspot costs fewer modules.

Sizing on metal

Laser-marked metal holds fine detail, but keep modules at 0.5 mm or larger, below that, oxide-layer variation and surface texture start flipping samples. A version 3 code (29 modules, 37 with quiet zone) at 0.5 mm is an 18.5 mm square: metal tags carry serious payloads in small footprints. Run the payload through the size calculator against the reading distance, and mark a border or leave clean metal for the quiet zone, a code tight against a tag's stamped edge fails.

Where metal is the right answer

Metal wins when the code must outlive every printed alternative: asset tags, plant and machinery, memorial plaques, trail markers, anything facing weather or handling for a decade-plus. The lifetime table in outdoor durability puts anodised aluminium at 10–20 years and annealed stainless at decades, and when a weatherproof sticker tops out around seven years, a metal plate is the honest next step. Process details for buying engraving are on engraved metal and how to engrave a QR code.

FAQ

Does a laser-engraved QR code on metal scan?

Only if the process creates real luminance contrast. Laser annealing on stainless makes genuinely black modules and scans well. Plain engraving without infill relies on shadows and scans unreliably, fill it with black enamel or choose annealing.

What is the best metal for a QR code?

Stainless steel with laser annealing for maximum life and a smooth surface, or photo-anodised aluminium for print-quality detail at lower cost. Prefer brushed or bead-blasted finishes over polished to control glare.

How small can a QR code be on metal?

Keep modules at 0.5 mm or larger. A short-URL version 3 code at that size is an 18.5 mm square including the quiet zone, which suits most asset tags.

How long does a metal QR code last?

Photo-anodised aluminium is good for 10–20 years outdoors; annealed stainless and paint-filled engraving last decades. The mark usually outlives the URL it encodes: plan the destination accordingly.