Soak them in a solution of bleach and hot water (half and half). If I have a mug with teastains I fill it with bleach and water and stick the teaspoons in at the same time. Make sure you wash them thoroughly afterwards.
I get a mug, fill with a little washint powder and hot water and lave spoons in there for half hr or so then rinse..Find it works better than bleach as doesnt ruin coating.......