Wool, silk, and linen pre-mordanted with oak galls, and then modified with iron
Iron as a pre-mordant
In all of the natural dyeing I’ve been doing (or hoping to do!) in the last little while, I read a little about using iron as a pre-mordant instead of alum. In Rebecca Burgess’ Harvesting Colour: How to find plants and make natural dyes, she notes that while alum is used for most of recipes in her book, iron is useful in several.
Green oak galls
I’ve read about oak galls and their place in dyeing and ink-making a little, and didn’t think too much of them – I don’t really think of oak trees in Calgary (compared to trips to Louisiana!) but while out for a walk (playing PokemonGo!) I noticed that one of the parks near me had cute little (young) oak trees. A closer look… and there were the weird clustered balls.