Abstract: An apparatus for obtaining watermarks or patterns in paper or cardboard while being formed on a formation tape or table in a paper or cardboard manufacturing plant, comprising: a primary fibrous mix source for storing a primary fibrous mix; at least one manifold, which can be arranged proximate to the formation table; at least one jet nozzle which can be fed by the at least one manifold and is arranged above the formation table so that it can be angularly adjusted with respect thereto; a feeding duct for a secondary fibrous mix and a return duct from the at least one manifold; and a secondary fibrous mix source arranged to supply the feeding duct and to receive material discharged from the feeding duct for return from the at least one manifold.

Abstract: A method for producing watermarks or patterns in paper and cardboard which can be performed during a process for manufacturing the paper or cardboard comprises the following steps: preparing a primary fibrous mix of cotton cellulose based on alpha-cellulose with the addition of sulfate cellulose; preparing a secondary fibrous mix which has substantially the same composition as the primary mix but to which an adapted dye and/or pigment has been added; spreading the resulting fluid mix on a moving formation board of a paper manufacturing plant, so as to obtain a layer of very moist cellulose pulp designed to be dehumidified and stabilized along a preset path on the formation table; applying a jet or jets of secondary fibrous mix to the relatively fluid layer of primary fibrous mix so as to produce a recess as a consequence of the lateral displacement, with respect to each jet, occurring in the layer of primary fibrous mix, the recess being filled with the secondary fibrous mix by the respective jet; and amalgam