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I'm trying to strip the seasoning (polymerized oil) off a carbon steel skillet.

Following online instructions, I've prepared a lye solution, using tap water, 2.5% concentration by weight, which ought to produce results in a matter of days; two weeks in, it's still far from being done.

It occurred to me we have hard water here, 13 dKH/15 dGH, so I'm guessing the solution just isn't as basic as it was expected to be.

Heating it up isn't an option, so I'm planning to add more crystals of sodium hydroxide to speed the reaction up.

Assuming that my diagnosis is correct, and the instructions were based on tap water hardness that is typical for the US, how much more hydroxide should I be adding to compensate for the higher hardness?

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  • $\begingroup$ The water hardness wouldn't have any measurable effect. $\endgroup$ – MaxW Sep 9 '18 at 3:03
  • $\begingroup$ If you're just trying to clean the cooking surface, try some fine steel wool and a little elbow grease. $\endgroup$ – MaxW Sep 9 '18 at 5:24
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    $\begingroup$ Need a stronger solution. I don't know where you are based but here in the UK I can buy KOH in polyethylene glycol gel which cleans metal surface in a couple of hours. $\endgroup$ – Waylander Sep 9 '18 at 7:52
  • $\begingroup$ @Waylander How much stronger? While I do wear protection, I don't want to end up with a solution that requires too much extra care, like neutralization before disposal. $\endgroup$ – plco Sep 9 '18 at 21:19
  • $\begingroup$ @MaxW I am aware the coating can be removed mechanically, but that takes a ton of time and work. I tried and it's too much, which led me to giving up and buying sodium hydroxide, that I would have rather done without. $\endgroup$ – plco Sep 9 '18 at 21:22
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The short answer to your question is that the dGH of your water is negligible compared to the amount of lye you are using, so no adjustment needs to be made on the basis of hardness. 15 dGH corresponds to 150 mg/L or 0.015% as CaO, which is trivial compared to your 2.5% lye solution.

Other possible reasons for the slow cleaning process include the way in which the oil has polymerized (as a result of what has been cooked and under what conditions) and the quantity of polymerized oil present. Regardless, the means by which you can speed up the cleaning using your method are to increase temperature and increase lye concentration. If heating really is not an option for you, then you could try a 10% solution (as noted by Waylander in the comments). Disposal of this solution is not a problem, just dilute the solution first or during disposal by running water and pouring slowly. Many household cleaning products use lye so this really isn't an issue.

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