Auxiliary applicator device in a decoration station for ceramic tiles or slabs, said station being intended for the application of ceramic enamel on these latter, which are moved by a conveyor so as to enter said station, pass in succession by at least one spray nozzle arranged in the same station and finally exit said station, said at least one spray nozzle being carried by a corresponding carriage, operated by a mover in a direction crosswise to the forward one, with back-and-forth movements, the combination of said decoration station and said auxiliary applicator device being characterised in that said auxiliary applicator device includes: - at least one additional spray nozzle, fastened to a respective carriage that can be moved by a mover with a reciprocating movement parallel to the motion of said at least one ordinary spray nozzle, with said at least one additional spray nozzle maintained inoperative under conditions of regular operation of the aforesaid at least one ordinary spray nozzle; - a plurality of video cameras, at least one of them being provided for each of said ordinary spray nozzles and designed to take, in real time, images concerning the spray pattern generated by the relative ordinary spray nozzle in each of the back and forth operating cycles performed by the latter; - electronic processing means, designed to acquire images taken during each cycle by each of said video cameras and to compare them with a stored sample image (Vm), representing a spray pattern according to prefixed suitable specifications for a correct operation; - a control unit, interfaced with said electronic processing means and intended for deactivation and selective stop of one or more of the aforementioned ordinary spray nozzles whose pattern has been found non-compliant, with the same control unit also provided for selectively activating, in suitable phase relation, said at least one additional spray nozzle to replace the function of the ordinary one being stopped, for a period of time at least sufficient to allow service operation on the latter. - at least one additional spray nozzle, fastened to a respective carriage that can be moved by a mover with a reciprocating movement parallel to the motion of said at least one ordinary spray nozzle, with said at least one additional spray nozzle maintained inoperative under conditions of regular operation of the aforesaid at least one ordinary spray nozzle; - a plurality of video cameras, at least one of them being provided for each of said ordinary spray nozzles and designed to take, in real time, images concerning the spray pattern generated by the relative ordinary spray nozzle in each of the back and forth operating cycles performed by the latter; - electronic processing means, designed to acquire images taken during each cycle by each of said video cameras and to compare them with a stored sample image (Vm), representing a spray pattern according to prefixed suitable specifications for a correct operation; - a control unit, interfaced with said electronic processing means and intended for deactivation and selective stop of one or more of the aforementioned ordinary spray nozzles whose pattern has been found non-compliant, with the same control unit also provided for selectively activating, in suitable phase relation, said at least one additional spray nozzle to replace the function of the ordinary one being stopped, for a period of time at least sufficient to allow service operation on the latter.