The Insert Spec
This page is the spec a printed QR insert must meet before anything covers it. It says nothing about the encasement — epoxy, glass cabochon, laminate pouch, locket — because the encasement is your call. Meet these numbers and the method is yours. Miss them and no resin technique will rescue the code.
Usable code side by insert size
The code is a square, and on a circular insert that square sits inscribed inside the circle: its side is the diameter divided by √2. A square insert is kinder — the code keeps 94% of the width. These are the numbers for the six preset sizes the insert sheet tool offers:
| Insert size | Circle — code side | Square — code side |
|---|---|---|
| 20 mm | 14.1 mm | 18.8 mm |
| 22 mm | 15.6 mm | 20.7 mm |
| 25 mm | 17.7 mm | 23.5 mm |
| 28 mm | 19.8 mm | 26.3 mm |
| 32 mm | 22.6 mm | 30.1 mm |
| 38 mm | 26.9 mm | 35.7 mm |
Code side includes the quiet zone — it is the full printed square, not just the dark modules.
The 0.5 mm floor
Each little square in the pattern — each module — needs about 0.5 mm of print to scan reliably on a phone camera. That floor is why content and size are linked: a tel: code, which encodes at QR version 1 or 2 and produces the chunkiest grid, fits a 25 mm circle. A loaded vCard — pet name, two numbers, a note — carries more data, so its modules shrink, and it generally needs a 32 mm or larger circle, or a square insert. The generator does this arithmetic for every preset and tells you plainly when a size will not work. Believe it. It refuses to pretend otherwise.
The quiet zone is part of the code
Every code carries four modules of white space on all four sides. That border is not padding — it is how a scanner finds the edges of the pattern, and it is generated inside the printed square. Cut on the guide lines and the quiet zone survives automatically. What you must never do is trim tighter to "lose the white border." A code trimmed into its quiet zone can fail even when every dark module is intact.
Contrast
Dark modules on a white ground. Phone cameras find codes by contrast, and every step away from black-on-white spends margin you will want later, when the tag is scratched and the light is bad. Avoid tinted paper, colored washes, or metallic grounds behind the code. Decorate the rest of the tag however you like — the spec covers only the square the code sits on.
Flatness
A heavy dome of clear resin is a lens. It magnifies the center and distorts the modules near the edge, which is exactly where the position markers live. Keep the face over the code flat or low-domed. If the piece wants the domed jewelry feel, dome the back and leave the code side flat. The epoxy guide shows one proven way to get there — it is one method, not the method.
Test before you commit
Every code downloaded from this site was already machine-decoded at three raster sizes before the file reached you — but that verifies the file, not your print. Printers drift, toner runs light, and a sheet printed at "fit to page" instead of 100% scale shrinks every module below the floor. So test the physical print before anything covers it: cut one insert, set it on the bench, and scan it from 30 cm away in poor light — a dim hallway, not a lit desk. That is the scan a stranger will actually attempt, crouched over a nervous dog at dusk. If the print passes at the bench, encase it. If it fails, fix the print now, because resin is permanent and so is the failure.
Selling tags built on these codes is welcome — no attribution, no license, no strings. The maker page covers that side; this page is the part your customers never see and always depend on.