Small squares of blotting paper attached to disposable plastic strips are impregnated with pH sensitive compounds usually extracted from lichens, especially Roccella tinctoria.
After a period of small subsistence agriculture, the local economy began to concentrate on a few chief exports: initially, lichen (Roccella tinctoria) and woad (Isatis tinctoria), later the introduction of wheat and corn crops.
Isatis tinctoria | Roccella tinctoria | Indigofera tinctoria | Genista tinctoria | Alkanna tinctoria | Weinmannia tinctoria | Roccella Ionica | Morinda tinctoria | Maclura tinctoria | Leea tinctoria | Gunnera tinctoria | Ficus tinctoria | Chrozophora tinctoria | Baptisia tinctoria |