The debate raged for years (at least in those circles where things like this inspire rage): Which museum had the genuine article? Both the UK National Gallery and the Carnegie Museum of Art in Pittsburgh laid claim to Virgin and Child with an Angel by Renaissance artist Francesco Francia, and most experts agreed that the one in London was legit. That is, until last year when the organic chemistry of the painting was studied using something called a gas-chromatography-mass-spectrometer. In the hands of researchers, a GC-MS is used to determine the composition and characteristics of paint binding media, resins, varnishes, and obscure pencil marks -- which, in the case of the Francia, proved that the painting is in fact a 19th century forgery (graphite not being available to Francia in 16th century Italy). Don't feel bad, London. We've all been fooled by international art forgers at some point.