A method of determining the suitability of continuously cast slabs of Al- or Al-Si-killed soft steel for producing cold rolled sheets to be tinned, comprising taking a transverse sample of a length of between 50 and 150 mm by making parallel cuts perpendicular to the thickness of the strand and making a slanting cut in the sample, which cut starts from one end of the sample from the surface thereof and is 30 mm deep at the other end of the sample, thus creating a slanting cut area, subsequently making a Baumann print of the slanting cut area showing inclusion clouds present as brown spots, thereupon planimetering the whole inclusion-clouds-area and putting the planimetered area in mm.sup.2 in relationship to the slanting cut area in dm.sup.2.