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My guess is that the saponification reaction is only dependent on the concentration of $OH^{-1}$ ions and of course the coposition and concentration of fats. I also guess that the fat part of the situation is rather constant. My guess means that the cation would have no or negligible impact.

This would suggest that the degree of slipperyness would be only pH dependant (and not dependent on the cation). Does this mean that there is a certain pH level where the solution starts to feel slippery? If that's the case about which pH level is it?

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    $\begingroup$ Why won't you go and check it yourself? Chemistry is an experimental science, after all. I'd say it starts around pH=9. Besides, the feelings are subjective, so we tend to rely on instrument readings whenever possible. Haven't heard of a slipperymeter, though. $\endgroup$ – Ivan Neretin Oct 27 '17 at 11:18
  • $\begingroup$ @IvanNeretin Yes, but perhaps my question was not that clear about that the question was a bit about if it's only pH that plays a role. That is that if I test with sodium hydroxide for example would that mean that the findings are valid for other bases as well? Also a part of the question is whether saponification occurs only above some certain pH or that it's just that it's below the sensory threshold (I guess that your comment implies the later) $\endgroup$ – skyking Oct 27 '17 at 12:17
  • $\begingroup$ Well, with NaOH, KOH, etc., it is just pH that plays a role. Other than that, chemistry is rich and diverse; one can imagine certain compounds which are not alkaline, yet still slippery. $\endgroup$ – Ivan Neretin Oct 27 '17 at 12:21
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There probably is no one pH level where things get slippery. Capacity to react as a base has something to do with it.

You can make ammonia and sodium hydroxide solutions both with pH 11, but the sodium hydroxide solution is only 0.001 molar and thus cannot react with much oil on the skin. Ammonia solution has a lot more base available to react with those fatty acids. The weak base "hides" most of its reactivity in water alone but reveals when there are fatty acids to neutralize, so it's slip sliding away.

Probably anything that we consider basic and is sufficiently concentrated will slip in the fingers.

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