Chromatic Variation in Late Antique Rainbows

Depictions of rainbows in late antique and early Byzantine art follow the normal sequence of the spectral colours, only some bows exclude blue and violet. Another characteristic feature of the late antique rainbow is the inclusion of white and the non-spectral hue pink. In order to investigate chromatic characteristics, I use as case studies the comparatively few extant rainbow images of third- to sixth-century date from Thessaloniki, Constantinople, Rome and Ravenna. The rainbows, depicted in a floor mosaic, three illuminated manuscripts and three monumental wall mosaic decorations, are either part of narratives or rainbow-patterned borders used to frame other scenes. To throw light on the chromatic variations, ancient descriptions of rainbows are brought into the discussion and the representations are seen in relation to meteorological research. I propose that the late antique rainbow images follow two visual traditions, both of which can be traced back to the Hellenistic period and both of which are grounded in scientific research. One is the sunrise/sunset rainbow that ranges from red to green. I argue that the exclusion of blue/violet may be due to its being more difficult to see against the sky, the wavelength of violet being closest to the boundary beyond which coloured light tends to look black. The variant type, found especially in the church mosaics, covers the whole spectrum from red via green to violet as well as pink and white. I suggest that the non-spectral pink hues can be understood as the gradations of red that can sometimes be observed in the natural bow and that the white band provides highlight, which combined with a silver line indicates a strong luminance.