As described in the method section, the flow cell was kept constant at the desired temperature for crystallisation, and the process was monitored with both terahertz spectroscopy and an optical probe. Confirmed by visual analysis, crystallisation was usually observed to start at either inlet or outlet (or both) of the crystallisation cell, followed by crystal growth across the cell to its other end. Acquired images were useful complementary information to track the progress of crystal growth throughout the cell. After performing image edge detection and binarisation, crystals were represented by white pixels, and the amount of crystals in the field of view of the camera was quantified as demonstrated in Figure . In most measurements, it took approximately 4 min to 10 min for crystals to grow from one end of the cell to the other once crystal growth had initiated.