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Uncoated Zinc Oxide: Managing Tint and Finish in Sunscreen Formulations



Tinting is the most common issue when formulating with zinc oxide. It can happen across all skin tones, product types, and zinc oxide levels. The reason is simple: zinc oxide particles scatter visible light, which creates a white cast on the skin. Understanding this is the first step in reducing or controlling it in a formulation.



Getting Tinting Right


White cast and tinting are connected problems. Both come down to how well zinc oxide particles are dispersed in the final formula.


When zinc oxide is poorly dispersed, iron oxides cannot blend evenly around the clumped particles. The result is patchy colour, uneven skin tone match, and a formula that looks neither transparent nor tinted. Just inconsistent.


Uncoated zinc oxide is well suited to tinted formulations. Without a surface coating, the particles interact more freely with iron oxides and other mineral pigments, allowing for smoother, more consistent colour development. When dispersion is controlled, uncoated zinc oxide produces even, repeatable tones across batches.


ZinClear® XP is designed with this in mind. Its tight particle size distribution and compatibility with standard cosmetic dispersants make it a reliable base for tinted SPF, BB creams, and hybrid cosmetic-sunscreen products.

Advance ZincTek manufactures non-nano uncoated zinc oxide powders and ZinClear® dispersions under TGA-licensed GMP conditions in Queensland, Australia.



How Particle Structure Helps


This is the principle behind ZinClear® IM dispersions. The ZnO particles carry a porous internal structure that narrows the refractive index gap between particle and carrier oil. The result is a higher degree of transparency at a given concentration, despite primary particle sizes that remain firmly non-nano.


ZinClear® XP is available as both a powder and a range of pre-dispersions in carrier oils. In powder form, the particles agglomerate when dry but break down fully under high-shear dispersion, yielding a finer effective particle size in the final formula. In pre-dispersion form, that breakdown has already been done. The particles are stabilised in the carrier oil and ready to incorporate. In both cases, the outcome is a finely dispersed particle size that minimises white cast in finished products.



Technical Summary


Zinc oxide has a refractive index of 1.9 to 2.0, compared to approximately 1.4 for skin tissue. Particles in the 200 to 500 nm size range scatter visible wavelengths most efficiently, producing the white cast observed in non-nano formulations. Zinc oxide produces a lower whitening effect than titanium dioxide (refractive index approximately 2.6) at equivalent concentrations, due to its lower optical contrast with skin and carrier media (Araki & Baby, 2025).


UV protection by zinc oxide is delivered primarily through semiconductor band gap absorption, not reflection or scattering. UV-range reflection accounts for only 4 to 5% of incoming light, equivalent to less than SPF 2. Visible light reflection, by contrast, reaches up to 60% at wavelengths above the band gap range. This is what drives the white cast (Cole et al., 2016).


When zinc oxide particles agglomerate, they behave optically as larger particles, increasing visible scattering and reducing active UV-scattering surface area. Dispersion quality therefore determines both optical transparency and SPF performance. Transparency can be used as a practical marker for dispersion consistency during production (Cosmetics & Toiletries, 2025).


A porous particle microstructure reduces visible scattering by introducing air voids that bring the particle's effective refractive index closer to that of the surrounding medium. This approach reduces whitening without requiring particle sizes below 100 nm (Cosmetics & Toiletries, 2014).


Uncoated zinc oxide is the preferred base for tinted mineral formulations. Without a surface coating, particles interact directly with iron oxides and mineral pigments, supporting more even colour dispersion and consistent tonal output across batches.



References


Araki, M. S., & Baby, A. R. (2025). New perspectives on titanium dioxide and zinc oxide as inorganic UV filters: Advances, safety, challenges, and environmental considerations. Cosmetics, 12, 77. https://doi.org/10.3390/cosmetics12020077


Cole, C., Shyr, T., & Ou-Yang, H. (2016). Metal oxide sunscreens protect skin by absorption, not by reflection or scattering. Photodermatology, Photoimmunology & Photomedicine, 32(1), 5–10. https://doi.org/10.1111/phpp.12214



Cosmetics & Toiletries. (2025). Mastering zinc oxide formulation: A primer on overcoming challenges for superior sun protection. https://www.cosmeticsandtoiletries.com/formulas-products/sun-care/article/22940514/mastering-zinc-oxide-formulation-a-primer-on-overcoming-challenges-for-superior-sun-protection




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