So today was coffee station deep clean day including descaling my coffee maker.
After running the descaling solution through the coffee maker, I wanted to soak the shower head in the solution since it was pretty hard hit with scale and the brief contact with the solution while brewing wasn’t enough to clean it up.
So I dumped the hot descaling solution in a stainless steel bowl with the shower heat and left it to soak.
When I came back to check on it (30-60 minutes) everywhere the bowl was in contact with solution was purple. When I touched the purple tint it turned black (I really regret not having taken a photo at this point). It turned out the purple was just residue but the black underneath was (etched?) into the bowl.
I tried scrubbing with dish soap and water, which helped a bit but the bowl was still dulled and dark where it had been in contact with the solution. I then hit it was barkeepers friend which left me with what you see in the photo.
I guess my question is “what the heck happened?”. My best guess is that the bowl is not actually stainless steel and the solution ate off whatever was giving the bowl its shine? The shower head is also stainless steel and it was unaffected in this way. In fact the solution did successfully remove most of the scale build up on it.
Thoughts?
Purple always makes me think of manganese. Manganese is present in stainless but today I learned nickle can make purple too (yay pottery science lol) and nickle in the much more likely culprit in this case imo. Stainless steel bowls have layers of nickle oxide coating.
Some acids in decalers are reducing acids and others are oxidizing.
What chemical did you use specifically? I wonder if it was an oxidizing acid whereas the bartenders friend is oxalic acid and is a reducing acid.
You can buy hydrochloric acid (HCl) descalers but they not meant for stainless steel at least not all types (not 100% clear in this tbh). Here is a compatability chart.
You can see oxalic is okay for stainless but HCL is not.
I'm a fake chemist (chemical engineer) so take this with a grain of salt but I wonder if HCl liberated the nickel from the coating and it reacted with the EDTA to form the purple.
ETA: I'm asleep and didn't get the reason for mentioning EDTA out of my brain and on to the computer. Nickle forms purple compounds with cleating agents like EDTA. Cleating agents are often part of descalers/rust removal products. See figure 3 here: https://www.mdpi.com/2077-0375/11/3/165
ETA part two: this is not a kind edit and hypocritical because I am not an expert either but I don't understand all the comments about the bowl being aluminium. Yes, it's possible. But the internet is absolutely full of posts of people who used hydrochloric acid (also called muriatic in cleaning products) and fucking up their sinks. It's not an indication that the metal is not stainless.
Even the British Stainless Steel association says not to use it because it will fuck your shit up. https://bssa.org.uk/bssa_articles/cleaning-methods-for-stainless-steel/
There was a really good yt video about rust removal and descalers and the difference plus how they work including that it's often a calculated risk/concentration and contact time are super specific as part of that calculated risk. I am not finding it right now but I will take another look.
I used Dezcal descaler which appears to be Citric acid; Sulfamic Acid; and Sulfuric Acid.
And I’m just now realizing I misread the mixing instructions and used double the recommended ratio.
Should have been 100g/2L but I did 100g/L
Oh, okay that makes sense. I know we are talking about scale but this is relevant to the bowl: there are two mechanisms I know of to remove rust, one where the iron acts like the base in an acid base reaction to form a soluble compound and another where a chelation agent is used to form a soluble compound. Sulfamic acid does the acid-base reaction and is way harsher on metal than chelation.
Citric acid does both I think but more on the acid base side at lower pH. Either way, even at the more dilute concentration this product isn't something that metal is meant to sit in for long times especially if there isn't scale on there to react with more readily than the iron in steel. I will guess that's why the shower head was okay.
Barkeepers friend is oxalic acid which is another one of the cleating types. It is a reducing acid so it will counteract the oxidizing action of the sulfamic acid.
As for the purple I still think it's oxides of other components in the steel like nickle and chromium.
Sorry about your bowl 😔