The examination of two canvases painted at the same time, one by van Gogh, the other by Gauguin, provided an opportunity to document the disappearance of a pink color over large areas of both these paintings. It was found that the van Gogh, titled Deux Petites Filles had been restretched on a narrower frame, thus revealing an obvious loss of color on the exposed surface when compared to the previously hidden edges. The brushstrokes, examined by binocular magnifying glass, were determined to be by the same hand. Microscopic analysis performed on samples from the hidden areas and on slices taken from the raw edges confirmed the discoloration of a pink pigment that chemical analysis proved to be an Eosin lake produced and sold after 1871 under the trade name of Laque géranium; new considerations on the painting's original colors are presented as a result of these findings. Comparison of a Gauguin canvas with a student's copy of the same scene ( Dans les Lys ) -- copy which had been erroneously varnished but, protected by that coating, had not discolored -- , also led to the conclusion, confirmed by scientific analyses, that discoloration of the same pigment had occurred. Full-length English-language reports of the technical examination of the two canvases close this study. -- AATA