Twenty Microns Between Blueprint and Maybe Nothing

Dear the version of me two weeks from now, when the first spore print has been in the sun for nineteen hours and you still don’t know if it’s working:

The oyster mushroom from last week’s spawn jar finally matured. Severed the cap, laid it gill-side down on a sheet of glass, covered it with a bowl, left it overnight. This morning there was a perfect radial print—cream-coloured spores dusting out from the centre like a ghost starburst. That deposit is about 5-20 microns thick. Individual fungal cells, small enough that they’ll block ultraviolet light but nothing else.

Anna Atkins figured this out in 1843. Not with mushrooms—with algae. She was a botanist, friend of the Herschel family, and she took John Herschel’s cyanotype process and used it to document specimens by laying them directly on coated paper and letting the sun print them. Photographs of British Algae: Cyanotype Impressions became the first photographically illustrated book, though she never used a camera. Just contact. Biology pressing itself into chemistry.

I mixed the sensitizer tonight under the tungsten lamp: ferric ammonium citrate, potassium ferricyanide, equal parts in distilled water. The same chemicals I used for cyanotype printing back in March, except then I was printing cedar sprigs and leaving them in the sun for twelve minutes. Spores are different. They’re microscopic. They don’t block light the way a solid leaf does—they scatter it, diffract it, let most of it through. The exposure could take twenty hours. Maybe more.

Here’s what nobody mentioned until I went looking: alkaline-buffered paper degrades cyanotypes. Most archival papers are buffered with calcium carbonate to resist acid, which is great for longevity but terrible for Prussian blue. The alkalinity slowly bleaches the image over months. The mushroom cultivation guides already warned about buffered paper—it inhibits spore germination if you’re trying to culture from prints—so at least the materials align. I’m using Arches cold-press, unbuffered, the same stock from the darkroom.

Coated the paper with a foam brush, let it dry in the drawer, then placed the spore-dusted glass directly on top. No negative. No enlarger. The spores themselves are the mask. Where they’re thick, UV gets blocked and the paper stays white. Where they’re sparse, the ferric iron reduces and binds with ferricyanide to form ferric ferrocyanide—Prussian blue, the pigment that’s been used since 1704, the same compound they spread on soil after Chernobyl to trap caesium-137 in its crystal lattice. The chemistry that makes a photograph also decontaminates nuclear fallout. I still don’t know what to do with that.

The exposure frame is sitting on the porch now. Direct sunlight. It’s been four hours. The paper underneath looks pale bronze through the glass, which might mean it’s working or might mean nothing. Thin spore deposits from Lactarius species appear white but turn cream-to-yellow when thick. Density affects colour, which will interact with UV blocking in ways I can’t predict. Sparse radial patterns might let more light through than I want, creating darker blues where the gills were widest.

I thought about coating a microscope slide instead of paper—mycologists already place slides in the centre of spore prints for later examination under magnification. If I coat the glass with sensitizer, I’d get both the diagnostic print and a permanent photographic record in one session. But that assumes the exposure time works. And that the spores actually deposited densely enough. And that atmospheric pressure isn’t wrong—mushrooms collected at high altitude won’t produce reliable prints at lower elevations. Something about pressure differentials affecting spore release.

You’ll know by tomorrow whether this worked. Whether the radial gill pattern emerged as white lines in Prussian blue, whether individual spores resolved as texture, whether the twelve-micron scale was too small for UV wavelengths to care about. Maybe it’ll be beautiful. Maybe it’ll be a flat smear of blue with no detail. Maybe you’ll pull it out of the rinse water and it’ll look terrible—pale, washed out, disappointing—and then over the next hour as it oxidizes in open air the blue will deepen into something worth keeping. That’s what happened with the cedar print.

Or maybe you’ll realize that combining the patience required to watch mycelium colonize grain jars with the patience required for sixteen-hour photographic exposures was a miscalculation, and some hobbies synthesize better in theory than in practice.

Either way, the sun’s doing the work. You’re just waiting.