We have prepared face centered close packed arrays of polystyrene spheres using convective self-assembly. The optical properties of the arrays of spheres were studied and revealed high quality crystals that could be prepared using this method. Optical transmission measurements over a wide spectral range reveal the presence of multiple diffraction peaks. Their use for checking the quality of the arrays is proposed. The orientation of the arrays formed was studied using optical diffraction and atomic force microscopy. Both indicate the formation of oriented crystals. This was until now only reported for epitaxial growth of colloidal crystals. The oriented crystals were used to measure their photonic band structure. (C) 2003 American Institute of Physics.