Iodine was spilled on my cultured marblel/onyx sink. I've tried all types of cleaners; nothing has worked so far.

Doubt you will get Iodine stains out. You might try bleach on a rag and let it soak on it.

I found this,

Removing Iodine Stains From Marble (http://www.gsa.gov/portal/content/111914)

Stone Surfaces - How to Remove Iodine Stains | HowStuffWorks (http://home.howstuffworks.com/how-to-remove-iodine-stains3.htm)

Stain Removal | The Marble Man (http://themarbleman.com.au/blog/2011/07/27/stain-removal/)


What we can do to remove your stains
The most effective and common method used by a stone care professional to remove a stain from natural stone is to apply a poultice

And since I like videos

how to remove iodine stains from marble - Bing video (http://www.bing.com/videos/search?q=how+to+remove+iodine+stains+from+marble&qpvt=how+to+remove+iodine+stains+from+marble&view=detail&mid=4DA665F2C859771FD94C4DA665F2C859771FD94C&FORM=VRDGAR)

This is a series of videos but they all say make a poultice specific to the stain. Let me know if this helps.