A simple reproducible and reliable method to crystallize sub-micrometer-size spherical colloids using a mixture of volatile solvents as dispersion media is presented. Strongly diffracting direct opal structures of high uniformity are attainable over large areas within minutes and without further processing. Thickness and orientation control is also possible through this technique. In the figure, both [111] (left) and [100] (right) oriented lattices deposited on glass slides are shown.