pH strips aren't all that reliable
Ditto that. The surfactant nature of soap messes with the indicator chemicals on the strips and can throw your reading off by 2 to 3 units.
Also- pH won't tell you the most important thing- namely if you still have unreacted lye in your soap or if it is safe-to-use yet or not. The normal pH of lye-based soap can range anywhere from about 8.5 to as high as 12.4 and still be perfectly safe to use......... or not. A proper tongue test will tell you for sure.
Regarding the 12.36 pH-
in a dermatological Irritability Index test, Johnson's Baby soap with oatmeal (a lye-based soap) tested out at 12.4 on the pH scale and was rated the least irritating of all the soaps tested, while a Camay soap with a pH of 10.4 rated as most irritating. Go figure.
It just goes to show that pH does not tell the whole story and should not be used as the 'gold standard' indicator of a soaps safety or quality or comfort.
There's a lot of misinformation on the net regarding soap pH, as well as how to conduct a tongue test- such as directly licking the soap, etc...(wrong way/bad idea), but if you conduct the tongue test
the safe and proper way as explained by Dr. Kevin Dunn, it is highly unlikely you will ever get a chemical burn.
If you need to know the pH of your soap for other reasons, though (e.g. if your skin happens to be pH-sensitive), the best pH strips to use are
plastic lab-grade strips. They are much more expensive, but they are much more accurate than paper strips. To properly use any pH strips with lye-based soap (plastic or paper) you'll first need to make a 1% solution of your soap to test (i.e., don't test the suds or the soap directly). Take 1 gram of your soap and dissolve it in 99 g of distilled water, then test with the strip.
IrishLass