Flash Yellow If You're Already Watching

Halfway through sorting Diane’s bag of dried Phaeolus (dyer’s polypore, leftover from the mushroom extraction) I found a piece of bark with gray-green crust stuck to it. Not a mushroom. Lichen. The label said “Test this—different chemistry.”

Grabbed my phone. Googled “lichen spot test.” Found William Nylander, 1866, invented a diagnostic technique using potassium hydroxide to identify species that look identical. Downloaded a PDF key from a university herbarium site. Read for eighteen minutes standing up.

Then I mixed 10% KOH solution (drain cleaner dissolved in distilled water, measured on the kombucha scale), found a clean glass capillary tube left over from the mushroom spore prints back in February, and touched one drop to the gray-green surface.

It flashed yellow. Not “turned yellow slowly.” Flashed. The color appeared and started fading within half a second. I almost missed it.

Tried again, this time watching through a jeweller’s loupe. Drop hits the surface, yellow blooms outward in a ring, fades to orange-brown as the KOH oxidizes. The reaction is so fast you have to already be looking when the chemical makes contact, or it’s over.

That’s the K test. K+ yellow means the lichen is producing atranorin, a depside compound. But there are other tests. The C test uses calcium hypochlorite—household bleach, basically—and reacts with different secondary metabolites. Some produce red (lecanoric acid), some orange (gyrophoric acid), rarely green (dibenzofurans). The P test uses para-phenylenediamine, which forms Schiff bases with aldehydes and turns the specimen yellow to red if certain depsidones are present.

Here’s the strange part: you have to test both layers. Lichens aren’t uniform. The cortex (outer skin) makes different chemicals than the medulla (the white inner tissue). Species identification keys will read “Cortex K−, Medulla KC+ orange” because the surface might be inert while the inside reacts. Which means you scrape through with a razor blade, expose the medulla, then run the test sequence again.

The chemistry is destructive. You can’t identify a lichen without sampling it. And many species—especially in genus Cladonia—are “cryptic,” meaning they’re morphologically identical but chemically distinct. Same gray-green shrub, different secondary metabolites, separable only by whether PD turns them orange in five seconds or thirty.

Microlichens aren’t small, by the way. The term doesn’t refer to size. It refers to growth form. Anything crusty is a “microlichen” even if it covers a square meter of rock. Leafy and shrubby forms are “macrolichens.” The terminology is from 1866, same year as the spot tests. We’re stuck with it.

I need to make fresh C test reagent—the bleach solution breaks down in 24 hours, faster if you leave it in sunlight—and I need para-phenylenediamine, which stains everything it touches and lasts about a day unless you make Steiner’s solution (PD + sodium sulfite + detergent, lasts months, less intense colour).

Also I need to stop thinking about coordination chemistry and reactive vessels and whether the copper pot from the dye bath would interfere with lichen spot tests.

Also I have a meeting in twelve minutes.

I’m not ready.