While we are looking for a supply of 0.2-0.3mm (0.010") or thereabouts black, waterproof plastic, stiff and highly opaque. Vinyl, acetate, HDPE, polycarbonate, PEEK, etc. Also, we need to find a similarly sized paper or fiber product, and that got me thinking:
You have to wonder about the metric system in photography. The earliest days of Daguerre and Fox Talbot were full, half and quarters - fractions of plates. The 4x5 and 8x10, 20X24 and more are all English. 35mm is obviously metric. (is it, really? You might be surprised) 6x6 and 2/14x21/4 coexist peacefully, if inexactly. When we say 6X7 we know that means cm and when we say 4x5 we know that means inches.
The inch, foot and mile are based on human scale. The Who "I can see for miles", Shakespeare's "pound of flesh" and the runflat tires on all new BMWs and Mercedes are permanently and immovably entrenched in the so-called Imperial system, which many loathe. Photography the art is cultural. Photography the science is industrial and technical. Our little corner of the art is perhaps even a bit historical, having an affinity with the past, being analog, and we might even say human scaled, as we are apparently not digital (base 2) beings. One could extend the analogy to the metric system, with its rigors of base ten, convenient, yes, but then consider: Does it apply itself as well to us, and what draws us to the analog in art, and in music?