Blue residue on gas shut off valve

[Terry Beck]

Very pretty shade of blue residue on a gas shut off valve, would guess the gas lines were last inspected in 1959 based on the tag by a nearby furnace. My gas leak detector did NOT indicate a leak (though it did go off when I put it near the draft hood of a nearby 53 year old furnace).

Wondering what sort of chemical reaction would cause this? Suspect the valve is copper; would it be copper sulfate from condensation?

[Bob Harper]

Verdigris - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Verdigris)

Someone must have spilled something on it.

[Dom D'Agostino]

Someone sprayed it with soapy water to check for leaks, and didn't clean it off.

[Scott Patterson]

Someone sprayed it with soapy water to check for leaks, and didn't clean it off.

Yep, that is what it looks like....