Decent paring knife emerges from bleach-soap-water presoak with pitting corrosion. WTF?
Today as I was loading our dishwasher I noticed one of my semi-good chef's knives (a five-inch paring knife) had some odd black spots on the blade near the haft. After scrubbing it carefully I realized that the spots were pitting corrosion
I worked as a dishwasher years ago and an important technique for prepping the dishes and silverware for washing was the presoak, which helps prevent glutinous food waste from drying onto the surface of the dishes. I have adapted this in our house to be a small plastic tub kept in the sink with water, soap, and a splash of bleach in it. When a utensil is moved to the sink after use, if it's small, it goes into the presoak, used part down.
I had previously noted an increasing incidence of slight rust marks on some items coming out of the dishwasher and eventually realized it was due to a thrift-store table knife developing a crack in its presumably nickel-stainless chrome plate coating; the interior of the blade was rusting and gradually peeling the plate back from the cracked area. I didn't think about it much beyond noting it and decoding to junk it sometime.
This cracked knife was in the presoak along with the newly-pitted knife for about 18 hours, I guess. The linked wikipedia article notes that the presence of chlorides in solution can provoke an anodizing reaction that leads to this type of corrosion; I assume that the bleach in my presoak is the chloride needed.
Given that we have evidence that the corrosion has occurred in these circumstances, the short answer would be "don't do that," I think.
My specific question, though, is am I correct in fingering that cracked and rusty knife as the catalyst? I have been doing this presoak thing for years and had not ever noted pitting as a consequence previously.