The paper on the De iride and modern mapping of rainbow colour co-ordinates is published formally today in the Journal of the Optical Society of America A. Volume 31, Issue 4 – and the front cover is taken from our paper, with one of Hannah’s representations of the spectra from the scattering angle and droplet radius size. The spiral mapping diagrams are both beautiful and novel. The piece advances further the work carried out in this respect on the treatise on Colour in the same journal. The rainbow treatise was probably the last of Grosseteste’s scientific writings and represents a mature and reflective style.