I am having a problem removing white marks which I think are calcium deposits from my black granite Franke sink. Has anyone had this problem? If so, any recommendations would be greatly appreciated. Franke recommended Bon Ami multiple applications and once the stains were removed to coat the sink in vegetable oil once per week. I have done 3 Bon Ami scrubs so far with little success. I was told not to use Lime Away or any other such products.

Also, do you really have to dry the sink after every use? That seems ridiculous!