How did they print QR codes in the 19th century?

In anticipation of a print sale, I wanted to give buyers a way to pay for prints that would bridge the digital and analog domains, rather than living solely in the digital.

So I made a print of my Venmo QR code using one of the oldest means of photographic printmaking: the cyanotype.

I displayed the QR code on my laptop screen and photographed it on black & white film with a medium format camera, producing a negative about 60mm tall and 45mm wide.

With this negative I made a contact print onto some cyanotype paper I had already coated for other uses.

The contrast could be better, but this print passes the most important test: it scans with a smartphone!