Crottle

It was known and uſed as a dye-ſtuff in the Highlands of Scotland by the name of corkes or crottel, ſome hundred years ago.

Not that crotal and white was as humdrum as a simple definition of it as ‘brown and white’ implies. Crotal was the grey lichen which, over hundreds of years, had grown over the moorland rocks particularly

Parmelia omphalodes and P. saxitilis, the “crottles” used traditionally in Britain and Ireland, are sub-alpine lichens in North America.

The older people, they knew all about the dyes, and we’d go and gather the crottles [a kind of moss used for dyeing woolens]. I don’t know what you call them here. They were round and you’d scrape them off a rock or stone.

The Land Conservancy's lichen is a member of the genus Parmelia or "crottle lichen", and has strap-like lobes pale grayish above and black below. […] Some crottle lichens have been used in Scotland in the dyeing of wool for socks and Harris tweed since the 16th century. They yield a reddish brown color.