It can be water or oil soluble - I use the oil soluble because it repels water and adheres better to your skin. It's also good for including in anhydrous creations - like lipstick - or emulsified creations - like eye liner or mascara. Water soluble is just fine, but it will not adhere as well as the oil soluble if you have oily skin.
Titanium dioxide is chemically inert, meaning it is heat and light stable. It is easily incorporated into your creations - it won't clump up like zinc oxide, so it's a better choice for something thin (body milk consistency).
Titanium dioxide and zinc oxide are often used interchangeably or in combination in mineral make-up. Both are great for any product you make, but I'd use more titanium dioxide for medium to heavy coverage foundations. It adheres better than zinc oxide, so you'll want to use this in medium to full coverage foundations or eye shadows with lots of micas. Zinc oxide is great for skin protection, so you'll want to use more of that when you are looking for a foundation for sensitive or irritated skin.
SUMMARY OF TITANIUM DIOXIDE
Usage rate: 0 to 100% - I use 16% in my eye shadow base, 10% in my foundation base, and 25% in my blush base. I've seen it used as high as 45% in a foundation or concealer.
Whiteness or opacity: To make a colour lighter, to cover up imperfections.
Titanium dioxide is the queen of the whiteners and almost works too well. A great addition to medium to full coverage foundations.
Translucency: The base itself is almost invisible once applied.
Titanium dioxide is one of the least translucent ingredients you can use in mineral make-up.
Titanium dioxide can be used as a sunscreen, but I wouldn't count on it if you haven't tested it.
Slip: The product feels nice going on and staying on.
Titanium dioxide is not very slippery and can add some drag to your products.
Adhesion: The product remains on your skin.
Good adhesion, especially the oil soluble version.
Absorbency: Your colour will remain true throughout the day and not morph into something due to environmental stresses or skin oils.
Not really applicable here.
Light scattering properties: To give your skin a dewy glow.
Scatters light beautifully and can be used for this reason.
The queen of the whiteners, great for pastels and lighter shades. Can be used with darker shades to lighten them up!
Join me tomorrow for fun with sericite mica!