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In a home brewing project, I use washing soda (Na2CO3) to remove labels and glue from previously used bottles. In doing this, my flip-top bottles (which have a stainless steel flip top arm) often get unruly buildup of residual soda, which tarnishes and blemishes the steel. Is there a chemical mixture I can use to reverse this process and return the steel to a near-new appearance?

Here are a couple of photos of the bottles and buildup: the left shows a typical amount of residue; the right shows my attempt to wipe it clean with white vinegar (which partially works, but is still blemished).

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    $\begingroup$ Sodium carbonate per se should be soluble in water. You could try washing with abundant hot water. If it doesn't work, the residue could be some trace amount of calcium carbonate. Anyway, diluted vinegar or lemon juice are food-safe acidic chemicals which help dissolving the carbonates (by protonating them to the more soluble bicarbonate) $\endgroup$ – The_Vinz Jul 3 at 20:45
  • $\begingroup$ Can’t figure out what the downvoter of the question found bad about it. Perfectly fine question, well written, chemistry related, OP even added some pictures to illustrate it, go figure. I know this SE has lots of bad, usually homework, questions, but when a good question or answer is written we should kind of encourage it right? $\endgroup$ – IanC Jul 4 at 9:22
  • $\begingroup$ Eh, sometimes people downvote just because they don’t like it. Not the way SE is supposed to work, but 🤷‍♂️ $\endgroup$ – brandonscript Jul 4 at 17:00
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If you use tap-water together with Sodiumcarbonate, chances are that the residue is Calciumcarbonate (unless your tap-water is very soft).

Calciumcarbonate is significantly less soluble in water, but can be dissolved in acid. I would try to put a bottle/arm in a hot 5% solution of acid (acetic acid is fine, personally I would prefer citric acid) to see if any (small) gas-bubbles are formed at the residues. If it does, it is carbonate and can be removed in an acid bath.

If not, the residues could be glue from the labels, and getting rid of this is probably more complicated.

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  • $\begingroup$ I’ve tried with acetic acid, but still doesn’t work very well. I’ll try citric and see if that works (I’ll have to get some). Thanks! $\endgroup$ – brandonscript Jul 4 at 17:02
  • $\begingroup$ I don't know the strength of your acetic acid solution, but given time it should easily be able to dissolve carbonates. Citric acid has some advantages: it is a stronger acid and has some complexing and emulsifying propertis that help in dissolving residues other than pure carbonate. But be aware: citric acid (powder) often contains spores from Aspergillus that may cause mould in your product. The last step in the cleaning process should always be a rinse with pure water. $\endgroup$ – FrankS Jul 11 at 4:38

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