phenolphthalein stays clear, or very pale pink, then the soap is safe to be used on skin.
If it turns a deep pink, the soap should not be used on skin, but is safe to use for
household cleaning, dishes, or laundry.
You can also test the pH of your soap using a pH test strip, such as the ones
commonly used for aquarium water. Mix one gram of the soap with 100ml of room-
temperature water – the water should be just enough to dissolve the soap in, because
if there is too much water it will give a false pH reading. (Also, test the pH of the
water beforehand, and make sure that it is a neutral 7.) Use the strip to test the
solution, following the directions on the strip.
There is a third method to test for lye content, if you don’t have the materials
available for the other tests. Touch your tongue to the bar of soap, or touch the bar
with a wet fingertip and touch the fingertip to your tongue. If your tongue tingles, or
you experience a pinching or burning sensation, then there is still too much un-
reacted lye in the soap. This test can be somewhat dangerous; your tongue can get
burned if the lye content of the soap is very high. Also, you won’t be able to get more
than a very general idea of how much lye is in the soap, so this test isn’t highly
recommended.
STEP 14: STORING YOUR SOAP
! Page 37