Pressed powders are use to even out skin complexion. Pressed powders consist of fillers such as talc, mica, and sericite as well as pigmentary TiO2, iron oxides, microspheres, and liquid binder, and dry binder.
Talc consists of small platelets and comes in different sizes. It is easy to press because it is small platelets that slip together. Talc is found in many pressed powders because of its ability to press well. There is some concern about talc and asbestos. Talc has asbestos in its natural form but after it has been processed, etc and it is ready to be used in your product, it does not have asbestos anymore.
Mica consists of bigger platelets than talc. It doesn't press as well as talc and doesn't slip as well as talc. Large platelets are hard to press. It is shiny and transparent compared to talc. There is natural mica and there is synthetic mica. Synthetic mica has platelets that are more transparent, smooth and flat. Because synthetic mica is flat and smooth, it reflects more and acts like a mirror.
Sericite is a type of mica but it is older and more broken down. It whiter, softer, and more platey. It is also smaller and thicker than mica. Sericite is close to being a talc replacement.
There is also boron nitride, which makes a pressed powder feel very soft and silky.
The bulk of a pressed powder is fillers. There is also pigmentary TiO2 for coverage and yellow iron oxides, red iron oxides, and black iron oxides for color. Pigmentary TiO2 is different from the TiO2 that is used in sunscreen emulsions because it is much larger, greater than 0.2 microns (200 nanometers). Iron oxides are also greater than ~0.2 microns (200 nanometers). What is usually used in a American shade is 10-12% pigmentary TiO2 and iron oxides (7% TiO2, 3% yellow iron oxide, 1.75% red iron oxide, and 0.2% black iron oxide). For much darker shades you would use much less pigmentary TiO2 (such as 1%) and a more yellow, red, and black iron oxide. A Japanese shade contains more TiO2 than an American shade, ~10% TiO2.
Sunscreen actives can be used in a pressed powder if you want to claim SPF.
Microspheres are also great to add because they can absorb oil, add soft focus effect, and chance skin feel. Make sure to choose a microsphere that can be easily pressed. Microspheres that are perfectly spherical are hard to press.
Pearls can also be added for shimmer but they can be hard to press. Surface treated pearls are easier to press.
Using surface treated fillers, pigments, and microspheres are a good idea because the treatment helps the material press better. When treated the surface is smoother so they slide against each other and it is easier to press (they slip to lay flat). Another reason why it presses better is because there is less entrapped air because bulk density is higher.
Preservative is also added to pressed powder. Although pressed powders are anhydrous, water may be introduced into the pressed powder by the consumer so it is critical to have some preservative to protect against any microorganism growth.
Usually you need 6-7% binder to press. Liquid binder consists of esters, oils, or silicones depending on what is compatible with the other ingredients in your pressed powder, especially if you have surface treated material. You can include a film former in the liquid binder to help the powder adhere to skin. Dry binders, such as magnesium myristate, zinc stearate, etc, are also used to help press. Dry binders are predominately used in formulas with pearls.
