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Phenolphthalein for "Caustic Hot" testing

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January 31, 2016, 06:55 PM
The Eccentric
Phenolphthalein for "Caustic Hot" testing
I have been dripping phenolphthalein on my completed hot processed soap bars to verify they are neutralized. I notice that the phenol stays clear for several minutes, but when I come back there will be some pink. How does this test work? Will there always be some pink color turn given enough time? I have compared the results with a bar that just came out of cold process soap making and the phenol color changes quickly and is dark like it should be. I am surprised the hot process soap bar changes color at all because a pH meter reading at the end of of the cook step showed 8.7 which should be below the phenol color switch point.