Extender White (aka Ultra Silk Mica) is a blend of Mica and Titanium Dioxide. Its best use is as a"filler" or "extender" for matte cosmetics. It isrelatively translucent and non-whitening and also has a low luster.
If you are making a purely matte product you will want to thin down your intense, pure pigments (such as red oxide, brown oxide, black oxide, ultramarine blue ... ) with something that has good adhesion, relative translucency, and low luster.
In the past we've recommended our custom-blended TKB Matte Texture Base but, to be fair, Extender White is probably a better option.
Generally, you will have about 1/3rd Extender White to pigment. It will lighten the pigment shade.
California Residents: Warning: This product contains titanium dioxide which is [are] known to the State of California to cause cancer and birth defects or reproductive harm. Once the powder is incorporated into a liquid or solid base it can no longer be inhaled and therefore falls off the warning list. For more information go to www.P65Warnings.ca.gov
Warning: this product may contain trace chemicals (<10ppm Lead (Pb); <2ppm Arsenic (As); and <2ppm Mercury (Hg) listed by the State of California under the Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65) as being known to cause cancer, birth defects or other reproductive harm. The level of such chemicals complies with all Federal requirements under the Food, Drug and Cosmetic Act for safety and effectiveness.