Pinacyanol (synthetic dye)

Pinacyanol is a synthetic blue dye derived from coal tar that was used for sensitizing photographic plates, manufactured in the early twentieth century by the dye works of Meister, Lucius & Brüning at Höchst (near Frankfurt), Germany. It became associated with auric research thanks to the experiments of Oscar Bagnall, who continued from Walter J. Kilner's earlier research using dicyanin dye in his screens.

Preparation
In Dyestuffs & Coal-Tar Products (1915), the authors &mdash; Beacall, Martin, et. al. &mdash; relate that the pinacyanol is quinoline dye of the isocyanine type, reporting it is "obtained by treating quinaldinium salts with formaldehyde, followed by alkali."