These articles 3 a, 3 b are preferably, but not exclusively, of flattened shape, such as units for storage of optically readable data (CD's and DVD's, for example) and optically and/or magnetically readable cards, and have a surface to be printed, i.e. on which ink is to be laid, which is a reflecting surface or in any case a surface not adapted to be directly decorated without prior laying of a b