A box coating apparatus (10) for vacuum coating of substrates comprises a vacuum chamber (12) containing an evaporation source (14) and a substrate holder (16) formed as a dome vis-à-vis to the evaporation source and rotatable about an axis (R). A masking arrangement (20) is located in between for partially shadowing the substrates on the substrate holder relative to the evaporation source. The masking arrangement comprises a fixed masking portion (22) stationary in the vacuum chamber, and a plurality of gradient sector portions (24, 26, 28) carrying gradient shields assigned to the substrates on the substrate holder, for forming a gradient mask. The gradient sector portions can be rotated about said axis between a gradient mask open position where they are stored behind the fixed masking portion, and a gradient mask closed position where they are spread like a fan between the evaporation source and the substrate holder.