Make sure all your materials are clean and disinfected and ready to use.

Add phase B (niacinamide and glycerin) to phase A and stir until there is no sediment left on the bottom.

Check the pH; it should be between 5.0 and 5.5. This pH is not only best for your skin, but also ensures that the preservative can work optimally. Use a 10% solution (in demineralized water) of citric acid to lower the pH or a 10% solution of baking soda (in demineralized water) to raise it. Always add a maximum of 1 drop at a time, stir well and wait at least 1 minute before measuring again. As an indication: with 100 grams of mixture, 1 drop changes the pH by approximately 0.1 to 0.15 pH units on average. Work carefully and avoid over-adjusting.