I have a wrought iron handrail in my home that has black gunk on it about 1/32" thick in the groves. It comes off easily if I scratch it with my fingernail. The junk is not really noticeable, since it is black and who looks at a handrail anyway.
How might I go about cleaning the handrail without taking off the black finish? Soap and water? Gentle brush? Metal brush? Scouring powder? Chemical cleaners?