Too much lye? - A safe pH indicator from your kitchen

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Mar 23, 2009
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Those of you who took Chem 1 will remember phenothalein, brom thymol blue, etc., which are used to measure approximate pH of a solution. Most of these are synthetic dyes with some significant toxicity.

So to have a pH indicator that is not only non-toxic, but edible, is good to know. Years ago I learned to my delight that the yellow-colored spice, Turmeric, is a pH indicator. It's color-change is yellow at pH 7.4 (just basic of neutral) to red at pH 8.6 (which is still not "dangerously" basic. Hence it is perfect for determining whether you have too much residual lye in soap.

Before you use it for this purpose, it would be well to acquaint yourself with it's colors.
Take three white cups (or clear glasses placed over white paper) and put a tbsp of water in each.
To the first add a few drops of white vinegar; to the second, 1/8 tsp of baking soda; to the third, a few crystals of lye.
Mix a small amount of turmeric (maybe 1/8 tsp) with a tsp. of water (or better - alcohol).
Now put a few drops of the turmeric solution into each of the three cups.
The vinegar cup will retain the bright yellow color of the turmeric.
The lye cup will turn dark red.
The soda cup will take a color intermediate between these two colors, perhaps leaning a bit to the red.

So there you have it. If you don't know how to taste lye, or don't care to try, here's a definitive way of testing for too much lye. Traditionally, indicator dyes are made up in alcohol. Any alcohol will do - isopropyl alcohol, denatured ethanol (shellac thinner), methanol (gas-line antifreeze), or, if you want it to be non-toxic, vodka or Everclear.

For more information or other pH indicators, see the following link, but keep in mind that not all the "natural" indicators listed there are non-toxic. ... 60703a.htm

I'm a chemist. Which explains a lot.


Well-Known Member
Mar 19, 2009
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Cool! I had heard of using cabbage juice for this, but I think tumeric is much easier to keep around. :)


Well-Known Member
Oct 18, 2007
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Interesting, but the pH of a well made soap could be 9.5 or even higher... no free lye, just a naturally alkaline product

for bar soap I use my tongue. it's even cheaper LOL.

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