Whitening Water-in-Oil Serum Formulation Advice

Based on your intended formula and the previous discussion, here is guidance on your questions, taking into account the need to switch from Water-in-Oil EZ to Water-Capsule and the incompatibility between Ethyl Ascorbic Acid and Niacinamide.

First, it is essential to address the incompatibility. Ethyl Ascorbic Acid and Niacinamide are not compatible when combined in a formula, as this can cause the degradation of the Vitamin C derivative. You must choose to include either Ethyl Ascorbic Acid or Niacinamide in your formula, but not both. Consider the additional benefits of each ingredient (antioxidant for Ethyl Ascorbic Acid, barrier support/oil control/anti-inflammatory for Niacinamide) when making your choice.

Given the change to Water-Capsule, the mixing procedure will follow the staff's recommended three steps:

1. Prepare the Oil Phase: Combine all oil-soluble ingredients, including Water-Capsule, Dimethicone, Activated Resorcinol, MSH White, Natural Bisabolol, SKIN-DEFENSE® V, and ODA-White Plus™. Mix thoroughly using your available mixer until uniform. Gentle warming might be needed for some ingredients, but minimize heat exposure for sensitive components.
2. Prepare the Water Phase: Combine all water-soluble ingredients, including Purified Water, Disodium EDTA, GlucoBright™ (Acetyl Glucosamine), Rhamnose, Ethoxydiglycol, and Light Cream Maker (or Pro Polymer if preferred). Mix thoroughly until a uniform gel or solution forms. Add either Ethyl Ascorbic Acid or Safe-B3™ (Niacinamide) (whichever you choose to keep) to this phase and mix until dissolved.
3. Combine Phases: Pour the entire Oil Phase into the entire Water Phase all at once. Do not use the high-speed mixer at this stage. Stir the mixture quickly by hand for about 3-5 minutes until the Water-in-Oil emulsion forms and the texture is uniform.

Now, addressing your specific questions:

1) Mixing Oil and Silicone Phases Simultaneously: Yes, the oil and silicone components (like Dimethicone) are combined in the oil phase along with the Water-Capsule emulsifier before being added to the water phase for emulsification. This is the correct approach for the Water-Capsule system.

2) Adding ODA-White and Matrixyl 3000 in the Final Step: Yes, based on the product instructions, both ODA-White Plus™ and Matrixyl 3000 should be added in the final step after the emulsion has formed and cooled (below 40°C for Matrixyl 3000). This is compatible with the Water-Capsule mixing method and ensures the stability of these ingredients.

3) Reducing Mild Preserved Concentration: It is highly recommended to maintain the concentration of Mild Preserved™ (Ethylhexylglycerin) at 1% or use a suitable broad-spectrum preservative system. While Rhamnose and Activated Resorcinol have some antimicrobial properties, they are not sufficient to provide comprehensive preservation for the formula. Reducing the preservative level could compromise the product's safety and shelf life.

4) Adjusting for Kiehl's Hydro-Plumping Texture: To achieve a texture with more skin coating and a "juicy" feel, consider these adjustments:
* Increase the percentage of Dimethicone (e.g., from 5% up to 10%) for a smoother, more coating feel.
* Add a traditional humectant like Glycerin (e.g., 3-5%) or a Sodium Hyaluronate solution to the water phase to enhance the plumping and hydrated feel.
Be mindful that adding more ingredients can increase the potential for stickiness. You may need to experiment with percentages to find the desired balance.

By following these steps and adjusting your formula based on the incompatibility and desired texture, you can create a stable and effective whitening serum using the Water-Capsule system.