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If you're curious or actually knowledgeable about chemistry, here's what happened. My apartment's dishwasher has gaps in the enamel from which rust can drip onto plates and silverware. I tried soaking but I presume to be a stainless steel knife with a drip of rust on it in citric acid. The rust turned black and the water turned a dark but translucent blue/purple. I know nothing about chemistry. My smartest move was t…
I'm a little confused by your question myself. Stainless steel rust should be that same brown color. Though it can get very dark when dried. Blue is weird but purple isn't an uncommon description, assuming everything is still dark and there's lots of sediment. But what's the question? Are you trying to fix it? Just determine what's rusting?
Although, now that I look closely at them, the butter knife got eaten away in spots and it's already pretty cheap, so I'll toss it.