+ Buy a small bottle of "Iron-Out" at Walmart, etc..
+ Make a strong solution of Iron-Out -- 3 tablespoons in 1/2 cup warm water.
+ Dissolve as much as you can.
+ Saturate an old washcloth in the solution.
+ Then, while wearing plastic gloves, place the washcloth directly on a brown spot, and hold it there for a minute, pressing firmly.
If the brown is gone, or lightened, when you remove the cloth -- it's iron staining. Otherwise, I don't know what it might be.
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