Purple Above pH Nine, Clear Below

You’re about to find six dried brackets in a paper bag labeled “Diane—Hapalopilus,” and you’re going to Google the name before you do anything else. Good. Polyporic acid. pH-dependent pigment extraction. Purple above pH 9. You’ve done walnut tannin and aluminum sulfate. You know what metal-ion coordination looks like when it gives you pale tan instead of brown. Mushroom dyes don’t work that way.

First difference: ammonia. Not water. You simmer plant material in water and the tannins dissolve. Fungi hold their pigments at neutral pH. You need alkaline solvent—household ammonia, pH 11, breaks the hydrogen bonds and pulls colour compounds into solution. The term isn’t “mordant.” It’s “color catalyst.” Because ammonia isn’t fixing dye to fabric through coordination chemistry; it’s unlocking pigments that remain inert in hot water.

Hapalopilus nidulans produces polyporic acid, which only turns purple in alkaline conditions. Below pH 9 it stays clear or faintly yellow. Add ammonia and the molecule shifts conformation—proton loss exposes conjugated double bonds that absorb light in the 500-580nm range, reflecting purple. Same principle as pH indicator paper, but the compound is fungal metabolite, not synthetic dye.

Diane had written “no mordant needed” on the sticky note. I believed her, but cautiously. Soaked two brackets (about 30g dried weight) in 500ml water with 50ml household ammonia (10% solution, hardware-store grade). The brackets looked like dried coral—burnt orange surface, pale underneath, porous structure full of air pockets. Dropped them into a mason jar, poured the ammonia solution over them, screwed the lid on loosely so pressure wouldn’t build, left it overnight.

This morning the liquid was deep violet. Not purple-tinged. Violet. Darker than any plant dye I’ve seen. Poured it through a strainer into an enamel pot (not aluminum—reactive vessel chemistry matters here), added a scrap of pre-wetted cotton from yesterday’s mordanting test, simmered at 80°C for forty minutes.

Cotton came out lavender when wet, darkened to mauve as it dried. No mordant. Just ammonia extraction and cellulose uptake. The colour held through a rinse cycle—ran cold water over it for two minutes, watched purple water drain off initially, then nothing. Pigment had bonded directly to the fibre.

Here’s what I didn’t test: pot material. The Wikipedia table lists three outcomes for Phaeolus schweinitzii (dyer’s polypore) depending on vessel: copper pot + ammonia yields deep green, iron pot produces rust red, enamel or stainless gives orange. Metal ions leach into alkaline dye baths. Copper ions form different coordination complexes than ferrous ions. Same mushroom, same solvent, completely different colour output based on whether your pot is contributing Cu²⁺ or Fe²⁺ to the chemistry.

Diane showed me her copper pot—bottom half stained permanent green from years of Phaeolus extraction. She has three dedicated pots: copper for greens, cast iron for reds and browns, enamel for yellows and when she wants to see the “true” colour a mushroom produces without reactive-vessel interference.

I used enamel because that’s what was on the stove. Next test should be iron. Then copper. Then back to Hapalopilus in all three vessels to see if polyporic acid is similarly affected by trace metal ions or if its purple is independent of coordination chemistry.

Plant dyes and fungal dyes are structurally different. Walnut tannin is polyphenolic—big, complex molecules with multiple hydroxyl groups that coordinate with metal ions. Predictable chemistry. Add iron, get dark brown. Add aluminum, get beige. The molecular interactions are well-characterized.

Fungal pigments are weirder. Some are anthraquinones (similar to madder root). Some are terphenylquinones (not found in plants). Some are pH-sensitive indicators. Some fluoresce under UV. Phaeolus schweinitzii extracted with salt water produces a yellow dye that fluoresces. I don’t have a blacklight to verify this, but the Wikipedia table lists it, and Diane confirmed she’s seen it.

Fluorescent natural dyes are rare. Lichen dyes (orchil) do it. Certain minerals (uranium glass) do it. But plant-based textile dyes generally don’t. Fungal secondary metabolites operate under different biosynthetic pathways—mycelia produce these compounds as antifungal, antibacterial, or UV-protective agents. The fact that they also happen to dye fabric is incidental. They weren’t optimized by millennia of agricultural selection like indigo or woad.

You’ll find this frustrating because there’s no unified reference. Miriam Rice tested over 2000 mushroom collections and published “Mushrooms for Color” in 1980. That’s the foundational text. Before her, mushroom dyeing was folk knowledge—Norwegian wool dyers using Sarcodon imbricatus for blue-greens, scattered mentions in European herbals, nothing systematic. The current field guide is “The Rainbow beneath My Feet” (Bessette, 2001). Diane owns a copy. It lists species, extraction methods, and colour outcomes, but warns that results vary by substrate, harvest timing, storage conditions, and water mineral content.

Plant dyes have 9000 years of documented craft tradition. Fungal dyes have 44 years of systematic study. You’re working in a field where the reference material is younger than you are.

Hapalopilus extraction: worked. Colour: purple, saturated, fast. No mordant required. Used 30g dried mushroom per 500ml solution. That’s a 6% weight-of-fabric ratio if you’re dyeing 100g cotton. Comparable to plant dye concentrations.

Next test: Phaeolus schweinitzii. Diane has a bag of dried dyer’s polypore from last autumn. She says it produces yellows and golds reliably, greens in copper, reds in iron. Also: the fluorescence claim. If I can source a UV flashlight (the one from metal detecting is 395nm, might work), testing fabric under blacklight would confirm whether the salt-water extraction actually produces fluorescent yellow.

Also unresolved: whether white mushrooms (giant puffball, Calvatia gigantea) genuinely produce dark red with ammonia, as the table claims. The spore-bearing body is pure white. The chemistry suggests a colourless precursor that oxidizes or protonates under alkaline conditions—similar to indigo vat reduction, but pH-triggered rather than redox-triggered. Hard to believe until you see it.

You’re going to want to forage your own specimens. Don’t. Not yet. Identification matters. Cortinarius species produce purples, but some are toxic. Hydnellum peckii (bleeding tooth fungus) produces blues—rare in natural dyes—but resembles other stipitate-hydnoid fungi that don’t. Diane’s dried specimens are pre-identified. Use those until you’ve cross-referenced field guides and learned to key out saprotrophs from mycorrhizals, polypores from agarics, edible from merely non-toxic.

The walnut dye failure taught you that mordant chemistry is specific, not interchangeable. Mushroom dyeing is teaching you that dye chemistry itself is specific—pigment structure, extraction solvent, vessel reactivity all matter. Fungal metabolites don’t follow plant rules. They’re a different biosynthetic lineage producing colour for different evolutionary reasons.

Purple cotton is hanging on the clothesline. No iron, no aluminum, just ammonia and polyporic acid. Tomorrow: dyer’s polypore, three pots, comparative extraction. Maybe the UV test if the flashlight wavelength is close enough.

You’ll figure it out. Or at least figure out what you got wrong.

—Future you, Day 1.