This paper aims to verify if the classical theory of the diminution of industrial product prices in the long period is valid for raw silk between modern and contemporary age too. The author examines the case of the State of Florence compiling (using published studies and original sources) a list of raw silk prices from the end of the 15th century to the second half of the 19th century. The silk price diminution Tuscany had in that period was not caused by the growth of productivity (as the classical theory establishes) but, rather, by the increasing silk production that grew, in fact, more than ten times between 1500 and 1850. The classical theory is confirmed, instead, by the silk price movement in the State of Milan in the first half of the 19th century. Raw silk prices diminished quickly after the introduction of important technical innovations.