Abstract: A dyeing machine comprises a container (11) in which products to be dyed are placed, a source (12) of coloring liquids adding liquids on command into the container to realize a dye dip, and a unit (13) to circulate the dye dip with respect to the product. During the dyeing process a sampling and analysis device (14) automatically takes samples of liquid from the container at intervals and performs a spectroscopic analysis thereon. An electronic control and calculation device (15) receives the spectroscopic analysis data and calculates therefrom the concentrations of the various dyestuffs in the dip. The behavior thus obtained of the dip can be memorized for future use and/or can be used to command appropriate corrective parameters of the dyeing process.