Scannable, on slate.
Wi-Fi and pet tags that survive a laser: the levels, the margins, the inversion.
Which error correction — and for what
QR codes ship four error levels: L 7%, M 15%, Q 25%, H 30% of recoverable damage (ISO/IEC 18004). The app encodes level Q for the burned pieces — a laser engrave's rough edges eat more than paper's, and Q survives losing about a quarter of the code. Paper labels print at M: paper doesn't scorch.
The quiet zone is not decoration
Four modules of blank space around the code — the spec's quiet zone. Engraved tags routinely lose their margins, and a scanner reads the neighbouring engraving as part of the code. The app cuts tags with 3 mm of clear round the code.
Wi-Fi strings escape
Wi-Fi codes encode WIFI:T:…;S:…;P:…;; and phones read them — but \ ; , : " inside them must escape. The app does this for you; if you hand-encode, it trips more networks than it teaches.
THE trick for dark materials
A laser turns slate and black anodized aluminum light. So the code encodes inverted: the light modules and the quiet zone get engraved, and the dark surface reads as the code's dark. The app's test checks the inversion both ways.
The limits worth knowing
| rule | value |
|---|---|
| the caution | below 0.6 mm modules, test-burn first — a starting-point, not a measured figure |
| the maximum | 300 characters — longer codes need modules too small for a tag |
| the quiet zone | 4 modules round the code (ISO/IEC 18004) |
The honest footnote: the ISO spec and the app's own tests carry these; the module-size caution is the app's screen label — try your own material before the batch.