Here’s two forms of natural encrustation, both with their uses in island traditional crafts.
White Crustose Lichen : A relatively uncommon lichen, very slow-growing (this patch will have taken many years to form), and thus it is important to never remove any patch completely, and gather a very little from several locations. Fortunately, a very little goes a long way! Used for dyeing wool, the colour it yields is, ironically, black – or (depending on the mordant used) shades of dark grey.
Wild Ochre : Iron oxide, which settles out of the ground water or streams as a sludgy deposit, coating the stream bed and every scrap of vegetation. On our croft, there’s an ‘occasional’ stream (normally a mere trickle) that enters a cundy (a stone-built culvert) under a track as clear as glass, and emerges from the other end bright orange, and every so often J has to dig out the rusty sludge that accumulates and chokes up the ditch. No caution is required ‘harvesting’ this supply, as it seems to ‘grow’ howsoever fast as it is removed! An island craft potter has, in the past, used this ‘wild ochre’ from this location for use in her pottery. We haven’t found any mention of using this source of iron as a mordant – preparatory to dyeing wool : perhaps we should try!