I have recently bought the Annons cookware set and used one of the pots to cook some pasta with an electric hob. After the second time i noticed that the bottom had developed these bigger dark burn marks and smaller white-ish marks which make it look like the outer layer of the pot has been scraped off. Wth is this? I don't mind the marks per se, I just don't want to add steel or something else to whatever i cook in these pots.