St John’s Wort (Hypericum perforatum) is an incredible little plant. It can be identified by crushing the flower buds, which will release a beautiful deep plum liquid. This colour comes from hypericin, which gives an indication of the plant’s dyeing potential and is also one of its medicinal constituents.
The flowers and top few centimetres of each plant can be soaked in alcohol or oil to create herbal tinctures and oils. Over time, the hypericin in the flowers will turn the liquid a lovely deep red colour. Some of the medicinal uses include taking the tincture for depression and anxiety, and using the oil externally on aching muscles, cuts and tension headaches.
St John’s Wort can be used to create a dye bath, as Jenny Dean describes in her wonderful book Wild Color, but my very favourite use for it is eco-printing on paper. Pressed between pieces of watercolour paper, immobilised between 2 tiles and simmered under water for about an hour, it will produce a beautiful clear print with yellow and olive green leaves and blue and green flowers.
The paper can also be mordanted with iron, which has the typical ‘saddening’ effect on the plant dyes. The example below shows prints from the same plant which was pressed between iron-mordanted and unmordanted paper.