A magnetic assembly for producing an optical effect layer on a substrate, said magnetic assembly being configured for receiving the substrate in an orientation substantially parallel to a first plane and above the first plane, and further comprising: a) a first magnetic-field generating device comprising three or more first dipole magnets x31 ai (x31 a1, x31 a2,...), each of said first dipole magnets having its center C x31-ai (C x31-a1, C x31-a2,...) disposed on a loop in the first plane, wherein said first dipole magnets x31 ai (x31 a1, x31 a2,...) have their magnetic axes oriented to be substantially parallel to the first plane, wherein said first dipole magnets x31 ai (x31 a1, x31 a2,...) are at least partially embedded in a supporting matrix; and b) a second magnetic-field generating device comprising a second dipole magnet x41 having its magnetic axis oriented to be substantially perpendicular to the first plane and being arranged to have a projection of its center on the first plane be located at a projection point C x41 within the loop, wherein the second magnetic-field generating device is disposed above the first magnetic-field generating device, characterized in that angles α i are formed between each of the vectors C x 41 C x 31-al ( C x 41 C x 31- a 1,.,...) and the vector h x 31- al ( h x 31- a 1, h x 31- a 2,...) of the magnetic axis of the respective first dipole magnet x31 ai (x31 a1, x31 a2,...) wherein all of the angles α i, when measured in a counterclockwise direction, are in the range from about 20° to about 160° or in the range from about 200° to about 340°, and wherein each of the first dipole magnets x31 ai (x31 a1, x31 a2,...) is disposed at a first distance (Y i), said first distance (Y i) being on the first plane between the projection point C x41 and the center C x31-ai (C x31-a1, C x31-a2,...) of the first dipole magnet x31 ai (x31 a1, x31 a2,...). a) a first magnetic-field generating device comprising three or more first dipole magnets x31 ai (x31 a1, x31 a2,...), each of said first dipole magnets having its center C x31-ai (C x31-a1, C x31-a2,...) disposed on a loop in the first plane, wherein said first dipole magnets x31 ai (x31 a1, x31 a2,...) have their magnetic axes oriented to be substantially parallel to the first plane, wherein said first dipole magnets x31 ai (x31 a1, x31 a2,...) are at least partially embedded in a supporting matrix; and b) a second magnetic-field generating device comprising a second dipole magnet x41 having its magnetic axis oriented to be substantially perpendicular to the first plane and being arranged to have a projection of its center on the first plane be located at a projection point C x41 within the loop, wherein the second magnetic-field generating device is disposed above the first magnetic-field generating device, characterized in that angles α i are formed between each of the vectors C x 41 C x 31-al ( C x 41 C x 31- a 1,.,...) and the vector h x 31- al ( h x 31- a 1, h x 31- a 2,...) of the magnetic axis of the respective first dipole magnet x31 ai (x31 a1, x31 a2,...) wherein all of the angles α i, when measured in a counterclockwise direction, are in the range from about 20° to about 160° or in the range from about 200° to about 340°, and wherein each of the first dipole magnets x31 ai (x31 a1, x31 a2,...) is disposed at a first distance (Y i), said first distance (Y i) being on the first plane between the projection point C x41 and the center C x31-ai (C x31-a1, C x31-a2,...) of the first dipole magnet x31 ai (x31 a1, x31 a2,...).