Set a pan with a thin layer of water (approx. 1 cm) over medium heat. This will be your bain-marie.

Mix the glycerine and xanthan gum (Phase B) well together in a separate dish, until the gum is fully dissolved. Set this aside.

Remove both glasses from the water bath as soon as they are at temperature.

Use a stick blender and mix briefly in pulses of 5–10 seconds. As soon as the mixture turns cloudy, you know the emulsion has formed.

As soon as the mixture has cooled to below 40°C, add Phase D: vitamin E, preservative and optionally essential oil.

Check the pH; it should be between 5.0 and 5.5. This pH is not only the most pleasant for your skin, but also ensures that the preservative can do its work optimally.

Use a 10% solution (in demineralised water) of citric acid to lower the pH or a 10% solution of baking soda (in demineralised 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. The pH does not react immediately, so take your time to check before adding another drop.

For 100 g of serum, 1 drop changes the pH on average by about 0.1–0.15 pH points. Work carefully and avoid over-adjusting.