Silica for TiO2 Extension

https://www.hubermaterials.com/products/silica-and-silicates/paints-and-coatings.aspx 

The Zeolex® line of amorphous silicates are high performing, large particle size and prime pigment extenders used primarily in flat white paints to extend Titanium Dioxide. Up to 20% of Titanium Dioxide can be replaced with Zeolex products. Use of Zeolex products results in a much higher contrast ratio, tint strength, and brightness while providing lower sheen than conventional mineral extenders. Additionally Zeolex products allow much smoother, more seamless touch ups than competitive titanium dioxide extenders. For high quality paints, nothing compares to the seamless touch up that the Zeolex series offers.