Ascorbic acid (Vitamin C) in soap
What does it do in soap? Ascorbic acid and sodium hydroxide (NaOH) make sodium ascorbate in soap. Ascorbic acid and sodium ascorbate are both considered to be Vitamin C, an important dietary additive.
I do not know of any specific benefits that sodium ascorbate adds to soap, but if it behaves like other salts, it may increase the soap hardness when used in moderation. I do not know that this has been confirmed, however.
How much should I use? This acid is not often used directly in soap. Try 10 g ascorbic acid for every 1000 g oils (1% ppo).
How much lye does it neutralize? 10 g ascorbic acid neutralizes 2.02 g NaOH. 10 g ascorbic acid neutralizes 2.83 g KOH. When using ascorbic acid in your recipe, add the appropriate extra weight of lye needed to react with the acid. If you do not add extra lye, the acid will increase the superfat in your soap.
NaOH for ascorbic acid, grams = Ascorbic acid, grams X 2.02 / 10
Total NaOH, grams = NaOH for ascorbic acid, grams + NaOH for saponification, grams
Replace the 2.02 in the first equation with 2.83 to find KOH for ascorbic acid
Making a dual-lye recipe? For recipes that use both NaOH and KOH as well as ascorbic acid, please see my tips here....
How should I add it to my soap? Dissolve the ascorbic acid in about 2 times its weight of water. Stick blend that mixture into your oils.