During my brief, but chock full 'o informational interview with MAC Pro makeup artist James Molloy, last weekend at the IMATS he told me about an awesome professional product from MAC Pro called Face & Body Mixing Medium. This is the same formula as MAC's most popular milky and semi-opaque liquid foundation, however, this version doesn't contain any pigment.
It provides the skin with sheer and even coverage and is a great way to help you mimic the look of natural skin because of its satin sheen sans-shimmer finish. I didn't even know a product like this existed.
You can also use it alone, add it to any luminizer, or use it to thin out liquid foundations. James said it is often used to create hydrated, dewy looks and is a product commonly found backstage during fashion shows. Don't you just love learning secrets from the pros!