First, we need to test the pH of the finished bar. Do this before you plop it into a mould, do it when you’ve added all the ingredients.
Weigh 5 grams of the shampoo bar into a container large enough to contain at least 100 grams of water and your pH meter. It’s important that the pH meter electrode is covered.
Measure out 95 grams of distilled water or reverse osmosis water with a pH around 7 into the container with the 5 grams of shampoo bar.
Mix the solution of shampoo bar and distilled water- note that because SCI isn’t super soluble in water, it might not completely dissolve – with a small mixer or fork. You don’t want a ton of bubbles and lather, so mix slowly.
Test with a pH meter or more accurate type of strip. If the pH ranges from 7 to 7.5, your bar is awesome and you’re done, no pH adjustment necessary.
If the pH is too low, you can increase it with a titch of 18% sodium hydroxide solution or triethanolamine.
Start with 0.1 grams in the shampoo bar solution, mix, then test the solution with the accurate pH strip or pH meter. If the pH has risen to where you want it to be at pH 7 to 7.5, you know to add 0.1 grams 18% solution or triethanolamine. If it hasn’t risen, add another 0.1 gram to the solution, mix, then test again. Continue to do this until the pH is at the pH you want. That’s the percent you’ll add much you’ll add to the total shampoo bar batch, no matter what the size. If you used 0.1 grams, then add 0.1% to the shampoo bar batch.
After adding it, mix, then remove 5 grams for testing and start the process again until you have the right pH.
If the pH is too high, do the same thing by adding 0.1 grams citric acid/distilled water solution or just straight citric acid. Make sure it dissolves, mix, then test again. When the pH is where you want it, add that percentage to the shampoo bar batch. Mix, test again with 5 grams in 95 grams water, and so on until you get the pH you want.
Please note that every time you change anything in this bar, you will have to test and adjust the pH to see what that new ingredient or removal does to the product.