The QR code as material

A physical link

A QR code does not contain a page: it contains an address. It is a short piece of text, encoded as black squares, that a camera knows how to read back. Nothing else.

That is what makes it interesting material for the street. Stuck on a wall, a link becomes an object you only find by walking past it — an address that exists at one spot in the world. You do not search for it, you come across it.

And there is nothing to install. For some years now, the camera on every phone reads QR codes natively. A dedicated app has no point any more, and that is what makes a code on a wall usable by anyone.

Contrast beats colour

It is the mistake everyone makes at first: take your brand colour and turn it into a QR code. Ours is a violet, #7f22fe. On paper it looks good. To a scanner it is unreadable the moment the light drops.

A QR reader does not see colours, it sees light and dark. What counts is the difference in luminance between the squares and the background, not the hue. A mid violet on white has acceptable contrast in broad daylight and catastrophic contrast under a streetlight.

Our stickers therefore use a near-black violet, #1e1b2e, on white. That is our identity's neutral, not its accent. The brand colour is elsewhere on the sticker, never in the squares.

The practical rule: when in doubt, go darker. A code that scans at night also scans in daylight; the reverse is not true.

Error correction, and the logo in the middle

A QR code carries redundancy: some of the squares exist only to rebuild the information if the rest is damaged. There are four levels, from lightest to most robust, and the most robust tolerates about thirty per cent of the code being destroyed.

That is what allows a logo in the middle. The logo hides squares, and error correction rebuilds them. It is not magic: it is a budget being spent.

Our codes are set to level Q, which tolerates about a quarter of the code being lost. That is what leaves room for the question mark in the centre while keeping margin for whatever happens to the sticker outdoors — a scratch, a lifted corner, a drop of paint.

Going to the highest level has a cost: the code gets denser, so its squares get smaller at the same size, so it gets harder to read from a distance. More robust does not mean more readable.

The white margin is not decoration

A QR code needs a quiet zone around it: an empty band that lets the reader find where the code starts and where it ends. Without one, a code placed against a busy pattern becomes invisible to the camera.

That margin can come from the code itself or from what it sits on. On our stickers it is the sticker's own white that provides it: the printed square runs to the edge of the dark area, and the paper does the rest.

Which means a sticker that has been trimmed, cropped or stuck across an edge loses its quiet zone, and its readability with it.

Size, against reading distance

The trade rule of thumb is simple: the width of the code should be about a tenth of the distance you want to read it from. A five-centimetre code scans comfortably at fifty centimetres, with difficulty at a metre, and not at all from across the street.

Our stickers are five centimetres square. That is not an accident: they are made to be scanned by someone who stops and leans in, not by someone driving past. The placing charter says «at hand height», and that is the same constraint seen from the other side.

A code displayed higher up has to be bigger, in the same proportion. A five-centimetre code three metres off the ground will never be scanned by anybody.

What breaks a code outdoors

Glare. A varnished or laminated sticker facing a light source throws back a highlight that blinds the camera across a whole area. A matte finish scans better than a glossy one, always.

Curvature. A code stuck on a pole or a domed surface is distorted, and the reader can no longer find its grid. A slight curve is fine, a narrow tube is not.

Angle. A code placed very high or very low is read obliquely, which amounts to distorting it. Readers correct perspective a little, not much.

Time. Sun fades, rain lifts the edges, dust dulls the contrast. A six-month-old sticker scans less well than a new one, and that is normal.

What we learned placing ours

An unreadable code does not announce that it is unreadable. Nothing simply happens, and the person puts their phone away thinking the project is broken. That is the worst kind of failure, because it is silent.

So we test before sticking: take out the phone, scan the sticker while it is still on its sheet, then scan it once placed. Thirty seconds that save leaving a dead square on a wall for months.

And we test in the light of the place. A code that is perfect in a kitchen can fail in a dark passageway. That is where you discover a brand violet was a bad idea.

Why it works as street art

A QR code announces nothing. It has no title, no preview, no thumbnail. You do not know what is behind it until you have scanned it, and that is exactly what makes people want to.

It is also one of the rare forms of street art that damages nothing. A five-centimetre square of paper, on an authorised surface, comes off without a trace. The work is elsewhere: it is in what opens.

With us, what opens is a page with no owner, and the first person to scan it decides what it becomes. The code is only the door.