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I moved into this house a couple of months ago and bought some high quality stainless steel utensils with me from my house. I am noticing some black spots that don't go away with scratching or washing or baking soda. All my stainless steel kitchen utensils have this and some plastic containers have black dust which could be wiped with a dry paper towel.

My mum has been using the same set of utensils for years and has never observed anything like this. The only difference is that I wash my utensils with warm to hot water(and fairy dish soap).These spots also seem to increase in number(not in thickness) day by day. Have any of you heard or seen anything like this in stainless steel utensils ? What could this possibly be?

(There is a lining of black mold in the sealant lining the wall near the sink and also some in the shower which was scraped away when I moved in)

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    I don't know what it is, but there is no way it could be mildew infecting a polished stainless steel surface. Mildew would simply wipe away as you passed a finger over it. Looks to me like small pits in the S.S. surface, but I'm no expert on metallurgy.
    – Lorel C.
    Mar 29, 2018 at 1:01
  • Are you on well water in the new house? Normally you see this with people who salt the water for pasta before it's come to a boil ... but if you have hard water, you may want to consider a water softener to keep this from happening again.
    – Joe
    Mar 30, 2018 at 18:28

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The specks are corrosion pits. Austenitic stainless (aka- 18-8 , 304 , and several other numbers) are notorious for pitting in salt (halides). The 316 and 317 with molybdenum are more resistant but I doubt any cookware producer would go to the extra expense to use these alloys. However, I expect sitting for a couple days with salted water would be needed for pitting to develop. Out of curiosity, check it with a magnet; If strongly magnetic it is likely 13 Cr (410 SS) which would be likely to pit.

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  • Thank you very much for your opinion.Are the utensils still usable?or should I discard?
    – Sahoo
    Mar 29, 2018 at 11:31
  • U can use these utensils still
    – Me-si
    Mar 29, 2018 at 11:44
  • Thank you. How do get rid of it? or how do I prevent it from occurring in future. I use them for cooking and yes, I add salt while cooking but not any other time. Though I wash it within an hour or two after cooking.
    – Sahoo
    Mar 29, 2018 at 13:06
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    You can't reasonably remove them. Just wash and dry after use . It is unusual, I have stainless that I have not taken care of and had no pitting; I even have a 2qt pot with no handle that I have used 20 years in the garden for fertilizer, etc , and it has no significant pitting.
    – blacksmith37
    Mar 30, 2018 at 15:18
  • Well, the username pretty much makes this answer canonical.
    – Captain Giraffe
    Apr 22, 2019 at 2:56
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This type of black dot corrosion is seen from deposits of osmium dioxide and/or ruthenium dioxide, rare but far too common polluting metals that are often confused as mold. Precious metals, (gold, platinum, etc) after melting, will sometimes show black dot deposits on the bottom if they contain this rare impurity. Osmium contamination will oxidize in air when wetted with a basic solution, such as soap, forming volatile oily crystals of osmium tetroxide which smells of chlorine and very slowly attacks all type of metals leaving black dots. The dots usually form on metal after cleaning with bleach and tends to crystallize into golden (or bright red with amines) square crystals on ceramic/tile surfaces and into metallic flakes on organic/wood/plastic surfaces. black is very non-characteristic and can be due to many other possibilities so try spotting these other signs and pay attention to any chlorine-like odors coming from your homes heater although I realize you will likely never see this post, alas!

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  • Where would the Osmium and/or Ruthenium come from to deposit in a pan?
    – Tinuviel
    Feb 4, 2020 at 8:08

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