Control element for printed articles

1. A control element for a printed article, in particular for securities or the like, having a first drawing printed on a first side of said article, comprising at least a first set of geometrical shapes, which control element comprises a second drawing printed on a second side of said article, the second drawing being printed so as to face the first drawing and be in register with the latter, said second drawing comprising at least a second set of geometrical shapes corresponding to the first set of geometrical shapes, wherein said first and second geometrical sets include sectors which are offset so that, when a front side/reverse side register is correct, the control element has regions of variable density which are visible in transmitted light and wherein the offset sectors on the first side and the offset sectors on the second side are superimposed to form said regions of variable density, said sectors of the first set of geometrical shapes being offset along a direction which is opposite to the direction along which the sectors of the second set of geometrical shapes are offset.

2. The control element as claimed in claim 1 , wherein the first and second drawings are in perfect register so that the geometrical shapes of the first and second sets are superposed when viewed in transmitted light and said offset sectors create regions of higher density than that of the geometrical shapes.

3. The control element as claimed in claim 1 , wherein the first and second drawings are offset one with respect to the other in an alternating manner so that said geometrical shapes are not superposed when viewed in transmitted light and said offset sectors create empty spaces between said geometrical shapes.

4. A process for checking a front side/reverse side register of a printing machine comprising the steps of:

providing a printed article with a control element having a first drawing printed on a first side of said article, comprising at least a first set of geometrical shapes, which control element comprises a second drawing printed on a second side of said article, the second drawing being printed so as to face the first drawing and be in register with the latter, said second drawing comprising at least a second set of geometrical shapes corresponding to the first set of geometrical shapes, and wherein said second set of geometrical shapes includes sectors which are offset so that, depending on the front side/reverse side register being correct or incorrect, said offset sectors are respectively hidden by or visible between the geometrical shapes of the first set when viewed in transmitted light;

viewing the printed article in transmitted light; and

determining that the front side/reverse side register is correct or incorrect when said offset sectors are respectively hidden by or visible between the geometrical shapes of the first set;

wherein the first set of geometrical shapes includes parallel rectilinear lines of a given width and wherein the second set of geometrical shapes includes parallel lines having a width which is less than the width of said rectilinear lines and having segments which are offset along a perpendicular to the rectilinear lines, the offset of said segments being equal to the width of the rectilinear lines of the first set so that the offset segments are hidden by said rectilinear lines when the front side/reverse side register is correct and become visible between said rectilinear lines when the front side/reverse side register is incorrect and the first and second drawings on each side are offset one with respect to the other along a perpendicular to said rectilinear lines.