HELP! What's happening to my hot process soaping pot!

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Aug 23, 2021
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Portland, ME
I recently switched from crockpots/turkey roasters to a big lobster pot. The pot is new, and I made sure I got one that was 18/10 stainless steel so that there wouldn't be any issues with using the lye.
The first few batches I made turned out normal.
Yesterday I tried a batch that I hadn't made in a year. This time the bottom of my pot started turning a sooty black after it sat out to cool a couple hours after pouring my soap. I didn't notice this immediately after the batch was made which makes me think there was some type of corrosion or longer-term reaction that happened. The black rubs off on my fingers when I touch it, but is hard to get off with scrubbing, dish soap, and water. I have it soaking in vinegar right now. I make soap a LOT and I am afraid I'm going to wear through my pot! Does anyone have an idea on what might have caused this? Are there some essential/fragrance oils that do this to stainless steel and not others? The recipe I used involved both vanilla fragrance and cinnamon essential oil.

Nov 16, 2018
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Hamilton, New Zealand
That black stuff happens to all my (old) aluminium kitchen items when I put them in the dishwasher. I have a baking tray and a coated dish. the top coat says ok but the back of it goes black.
Maybe the pot has aluminium inside and it it's worn through?