These are caused by the silverware/flatware we eat with. I get them on my
ironstone dishes too. The advice of using Bon Ami is good, Bar Keepers
Friend also works well. I wrote to Pfaltzgraff about it on my dishes and
they sent me an order form for their expensive ironstone cleaner, sort of a
soft scrub like cleaner. It works no better than the much more reasonably
priced cleansers. I don't use regular cleansers with bleach in them though.
I love Bar Keepers Friend. It has a gold container. For the price we pay for
these ironstone dishes this should not be a problem.
Hope this helps.