After making CP soap and letting cure for a few weeks, is it necessary to test the PH? If so, what is the best way to test it? Strips, phenolphthalein?
BTW, please just don't tell me to taste it
Tasting will only tell you if lye is present and not the pH of it.
I personally don't test the pH of my CP soaps. I know this topic has been discussed quite a bit in the past, have you tried using the search option to read up on it?
If your concerned about having lye still be present in your soap, after several weeks the lye is gone. The saponification process is complete in about 12-48 hours (as a general rule) and the remainder of the curing process is so the excess liquid can evaporate. However if you mismeasured and used to much lye, then that's another issue.
Some are concerned about the pH being as close as possible to the skin of humans which is done by the balance of the oils used as well as the liquids used as well.
From everything I've read on the subject over the past 2-3 years, the pH of properly made, cured, CP soap will always fall around 10 to 10.5. This is based on the info I've gleaned from another forum I belong to we have a chemist on board. She's tested many CP soaps in the lab and she's never seen a properly made, cured, CP soap fall below 10. She uses a pH meter which is much more accurate than the pH strips which she says are notoriously off quite often by 2 or three points where soaps are concerned. Other soapers with pH meters have confirmed her findings. Their combined conclusion is that is quite a moot point to test the pH seeing as how it consistently comes to rest between 10 and 10.5 when the soaps are fully cured, no matter what you do to try to make it lower.
They say that a better test in order to make sure your soap is good to go is to just check for 'zap' or lye heaviness with the tongue test. Wait a few days after cutting your soap before doing it though, as the soap is still going through some chemical changes for those first few days and can still zap that early on, even though your batch is not lye heavy. I like to wait 2 weeks before tongue testing my soaps in oder to give the soap enough time and then some to go through its major paces. HTH!