The work included the penetrant inspection carried out on AlMg5 aluminium alloy provided with artificial discontinuities, i.e. pores (drilled openings). The tests involved the measurements of indication sizes depending on the time of development and various diameters and depths of openings. The dependences determined enable estimating the depth of pores in welded products made of aluminium and its alloys. The information obtained should enable the decision-making concerning the acceptance of a product for operation or the necessity of repairing it. The tests also included the determination of optimum indication development time for aluminium and its alloys.