Whatever Has Happened to This Fork? I left some dirty dishes over a summer internship.  Now, cleaning up, I have found that some of the silverware has developed a rough surface.  After sitting overnight in a soapy bath, it persists, although can be scrubbed off.

Here's a fork, which appears to be stamped stainless steel, showing the rough texture:


I don't have my microscope, and this camera image (try expanding it) is about as good as my eyes resolve.

My question: what is this?
I have seen similar deposited after stainless cutlery and plates were soaked in hard water from bores and from areas with hard water. Its just a collection of salts that like making a home on metal surfaces. You can remove it without scrubbing by adding some citric acid powder or a little white vinegar to some warm wash water. Denture cleaning tablets have a similar effect in cleaning off this buildup.

The citric acid powder is a really good way of cleaning up the built up scale in kettles and water heating appliances. It makes my glass electric kettle shine like new.