I just bought Berghoff Zeno stainless steel cookware. I washed one of the pots really good a couple of times with dishwashing soap and then when drying inside the folds and creases there was black residue that kept coming off. It still does.

Does anyone know what is this black stuff, and is it normal for new stainless steel cookware. Is it defective? I really love the feel and look of the set but I don't want to keep it if it's going to harm my health.

Thank you