Spectrum of cyanotype

This depicts original experiments with the Cyanotype process which includes 'specimens of some of the actual spectrum'. The test patches are marked A, B, C, D.

Experiments taken from Herschels journal entry for the Royal Society in November 1842 called 'On the Chemical Action of the Rays of the Solar Spectrum on Preparations of Silver and Other Substances, Both Metallic and Non-Metallic, and on Some Photographic Processes'.