Preventing Thickening in Matte Liquid Lipstick

The primary reason your matte liquid lipstick thickens is the evaporation of volatile solvents like Isododecane from the packaging. To minimize this, focus on reducing solvent loss.

Solutions

1. Packaging: This is the most critical factor.
   • Use high-quality, air-tight packaging specifically designed for volatile products like liquid lipsticks. The seal on the cap and the wiper inside the neck of the bottle are crucial for preventing solvent escape.
   • Ensure the bottles are filled adequately, leaving minimal headspace, but without overfilling which could interfere with the seal.
2. Manufacturing Process:
   • Minimize exposure to air during the mixing and filling process. Work quickly and keep containers covered as much as possible.
3. Storage:
   • Store the finished product in a cool place, away from direct sunlight or heat, as elevated temperatures will accelerate solvent evaporation.

Formula Adjustments (Consider with Caution)

Adjusting the formula can potentially help, but it might affect the matte finish, drying time, and wear properties that are characteristic of this type of product.

• Reduce Volatile Solvent Content: Slightly decreasing the total percentage of volatile solvents (Isododecane and Isohexadecane) could theoretically reduce the amount available to evaporate. However, this will likely make the product thicker initially and may impact spreadability and drying speed.
• Introduce a Small Amount of Less Volatile Emollient: Adding a small percentage (e.g., 1-3%) of a compatible, less volatile emollient that is soluble in the formula's base could help maintain fluidity over time. However, this might slightly compromise the matte finish and transfer resistance. Examples of emollients to consider (ensure compatibility with your base) could include certain non-polar esters or silicones, but this requires careful testing.
• Optimize Thickener Level: Ensure the concentration of Hectorite Gel is not higher than necessary to achieve the initial desired viscosity and pigment suspension. High levels of thickener will make the formula more sensitive to solvent loss.

Given your current formula relies heavily on volatile solvents for its matte, quick-drying performance, the most effective way to combat thickening is through optimizing your packaging and handling to prevent evaporation. Formula adjustments should be approached carefully, as they can significantly alter the product's intended characteristics.