Correct Order for Adding Preservative (Phenoxyethanol SA) to Silky Serum Base Plus
Question
I am making a facial serum using only water-soluble ingredients. I am using Silky Serum Base Plus to create the serum texture. I am confused about the step for adding preservative.
My current process is:
- Mix all water-soluble ingredients in water.
- Add Silky Serum Base Plus to create the serum texture.
- Mix for approximately 15 minutes until the serum is thick and viscous.
- Add the preservative Phenoxyethanol SA (not exceeding 1%) as the final step.
When I add the preservative in the final step, the serum immediately becomes liquid like water. I have to mix for another approximately 15 minutes to get the thick, viscous serum texture back.
Is this procedure correct, or should I add the preservative before incorporating the serum base as the final step? Thank you.
Answer
Correct Method for Adding Preservative to Silky Serum Base Plus
Based on the product information, your current method of adding Phenoxyethanol SA (eq. Optiphen Plus) in the final step, after the Silky Serum Base Plus has thickened the serum, is the correct procedure.
The description for Phenoxyethanol SA specifies that it should be mixed in the final step, at a temperature below 60°C and within a pH range of 2.0-6.0. Your process aligns with this instruction.
The temporary thinning you observe when adding the preservative is likely a physical interaction between the components of the preservative and the thickening system of the Silky Serum Base Plus. This is a known behavior with some ingredient combinations. Continuing to mix for another 15 minutes, as you've found, allows the formula to stabilize and regain its intended viscosity.
Adding the preservative before incorporating the Silky Serum Base Plus might interfere with the base's ability to properly hydrate and form the serum texture initially. The recommended method for Silky Serum Base Plus involves gradually adding the water phase to the base with stirring.
Therefore, continue with your current method of adding Phenoxyethanol SA as the final ingredient and ensure sufficient mixing time to achieve the desired serum consistency.
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