Make sure all your tools are clean and disinfected.

Put the niacinamide and D-panthenol from phase B in a small bowl and add a splash of your weighed water. Stir until everything has dissolved and the mixture is clear again, then pour it back into the rest of the water.

Pour the water into the paste little by little while stirring, so it doesn't clump. Then add the rest and keep stirring until you have a soft gel.

Check the pH; it should be around 5.5. This pH is not only the most comfortable for your skin, it also lets the preservative work at its best. Use a 10% citric acid solution (in demineralised water) to lower the pH, or a 10% baking soda solution (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. As a guide: in 100 grams of mixture, 1 drop changes the pH by about 0.1 to 0.15 points on average. Work carefully and avoid over-adjusting.

Let your serum rest for a day. This gives the xanthan gum and hyaluronic acid time to swell completely, and your gel turns lovely and smooth.