The lemongrass (Cymbopogon citratus) is a common herb in Southeast Asian kitchens, added into our curries and meat dishes for a special lemon zest kick, or simply drank as a refreshing tea. Usually, the stalk of the plant is pounded up (to release its full flavour) before being cooked with the dish. The plant is also used for medicinal purposes, more notably as an essential oil in aromatherapy. Research has also demonstrated promising results on its antibacterial, antidiarrheal, anti-inflammatory properties, linking them to her various phytoconstituents: flavonoids and phenolic compounds, terpenoids and essential oils.
We knew that the plant gives off a light yellow colour when brewed as a tea, so we wondered if we could get more colour out of it to be used as a botanical ink. We harvested about 50g of the leaves (cutting only the leaves and leaving the stalks to regrow), then cut down the plant material into smaller pieces to simmer for a start.
The essential oil of Lemongrass consists of 75-80% of citral (C10H16O), which appears as a pale yellow liquid with a strong lemon odour. This compound is probably the reason for its colour when brewed as a tea. As the main compound found in lemongrass, we were not so surprised when our pigmentation method yielded a lemon yellow as well. Addition of the salts created more opaque pigments, compared to when we were simply boiling it down as an ink.