Explanation for Yellowing and How to Fix It

The yellow color in your formulation indicates that the Vitamin C (L-ascorbic acid) has started to degrade. L-ascorbic acid is most stable in a low pH environment, ideally around 3.5. The other ingredients in your formula, such as Zinc PCA, Glutathione, Vitamin B3 (Niacinamide), GlucoBright™ (Acetyl Glucosamine), and Aloe Vera Gel, likely raised the overall pH of the mixture, causing the Vitamin C to oxidize and change color.

To prevent this degradation and maintain the effectiveness of the Vitamin C, you should adjust the mixing procedure and control the pH:

1. Mix all ingredients except the Vitamin C (L-ascorbic acid) first: Aloe Vera Gel, Zinc PCA, Glutathione, Vitamin B3 (Niacinamide), and GlucoBright™ (Acetyl Glucosamine).
2. Measure the pH of this base mixture.
3. Gradually add a pH adjuster like Citric Acid or Lactic Acid to lower the pH of the base mixture to approximately 4.0.
4. Once the pH is around 4.0, add the Vitamin C (L-ascorbic acid).
5. After the Vitamin C is fully dissolved, measure the pH again and adjust it further, if necessary, to reach the optimal stability range for L-ascorbic acid, which is around 3.5.

The current yellow color suggests only slight degradation. By adjusting the pH as described, you can significantly slow down further degradation and help preserve the potency of your Vitamin C serum.