there are also similar products that may be as effective but I have not tried them personally. I do know that chlorine bleach does not work on these.
Be VERY careful with this product, however. It contains HFl (hydrofluoric acid) which is nastier than HCl (hydrochloric acid). Always follow the instructions carefully!
Surprisingly (to me, anyway) a pumice stone works great for this. A friend recommended it to me when I had a similar situation to yours. I had a hard time believing the stone wouldn't scratch the porcelain bowl, but it didn't and removed the rings pretty quickly.
Best Answer
These appear to be rust stains. I've had reasonable success with a product called Wink:
Wink on Amazon
there are also similar products that may be as effective but I have not tried them personally. I do know that chlorine bleach does not work on these.
Be VERY careful with this product, however. It contains HFl (hydrofluoric acid) which is nastier than HCl (hydrochloric acid). Always follow the instructions carefully!