Hi Susan -- Unfortunately, we don't work with cast iron. Our care & feeding tips are only for stainless-steel. I wouldn't want to give you a product that we're not 100% confindent in backing.
Wow, a cast iron sink. I've heard of a cast iron pan (love mine), not a sink. Sounds like a great gourmet set-up.
Have cast iron built in bathtubs.....need them to shine too!
Try "Zud" rust remover. It is a wonderful product that is like Ajax and Comet, but geared more for cast iron. If it does not get it bright enough, there are companies that will re-glaze it.
It is covered with what I think is black enamel (spelling?). There are no chips, just dullness- almost like scratches from pots and pans. I recently tried Bar Keepers Friend which is like Ajax or Comet, but it didn't do much. I'll try and find "Zud" and see if that works. Thanks for the tip!
Susan, if it is a very old, true cast iron sink, it will probably need to have a new enamel surface applied to shine again. If the sink is say, 7years old, it may not be enamel but still is scratched & won't polish back. There may be products that can wax & buff a nice finish though.
There are companies that can refinish old enamel cast iron sinks and tubs. I had an old tub with a chip repaired and reglazed - good as new. Sprayed new finish, simple but smelly. Ventilation a must.
These sinks are covered with an enamel finish...and the dullness is due to finish wear. You can replace the whole sink or get it refinished. Refinishing in many cases gets close to the cost of a new sink...but you save in the installation dept. These refinish jobs are good but they never are quite as tough as the "baked" on finish from the factory.