Blue butterfly on the upper back

The Abbot has finally let me into the scriptorium on my own, which means I am now the one who must mix the blues. You will laugh, but the trouble is the butterfly. Brother Anselm painted it in the margin of the Psalter last week, a Morpho he called it, though none of us has seen one outside his cousin's travel stories. He ground the lapis so fine it lifted off the vellum like dust in a sunbeam, then laid soot and gum beneath the wings so they seemed to hover a finger's width above the page.

The shadow was too good. Brother Gerald, who keeps the bees, swore the thing had shifted when the shutters opened, and the novices refused to turn that leaf after dark. Anselm only smiled and kept painting. Then, on Tuesday, a real blue butterfly came in through the cloister window and settled on the wet ink. By morning the painted one had vanished from the margin entirely. Only its shadow remained, a grey smudge with nothing above it.

Anselm will not scrape the shadow away. He says it is the only honest part of any picture, because it shows where the thing wanted to be. He has asked me to leave that corner bare and paint nothing beside it.

I have capped the lapis pot. The real one returns each afternoon to the sill, opening and closing its wings in the heat, and the shadows it throws across the page are the nearest thing to a prayer I have seen this year. Write soon, and burn this letter if Prior Hugh asks.