How do I adjust the pH of a formula?
Short answer
Drop by drop, with a 10% acid solution to lower it or a 10% sodium hydroxide solution to raise it, checking after each addition.
Explanation
In the book's formulas, pH adjustment is the last phase (usually Phase E). Citric acid or lactic acid is prepared as a 10% solution (the toner uses 80% lactic acid in tiny amounts) and added a drop at a time, typically 0.2–0.5 g per 100 g.
What to do
- Stir thoroughly between additions and let the reading settle.
Source: The Big Book of Homemade Skin Care — Barrier Repair Cream (Phase E) and other water-based formulas