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He demonstrated with a sample of phthalocyanine blue, a synthetic pigment he picked out of a box that held paint cakes of different colours.

Martin has looked at so many of these spectra that he recognises on sight the patterns thrown up by different pigments, but even if he didn’t, the computer could rifle through databases of the spectrum patterns of other known chemicals, find the nearest match, and tell Martin what, in this case, he already knew: that his sample was phthalocyanine blue.