We study the transmission and reflection of electromagnetic waves propagating in bare opal photonic crystals. We find that the incomplete gap at theL point fully inhibits the transmission of waves propagating in the @111# direction for opal sample thicknesses that are easily obtainable. This property shows that bare opals could be good candidates for complete inhibition of transmission in the near-infrared and visible frequency range for given orientations. The dependence of the total reflectance on the angle of incidence has been calculated, and a good agreement has been found with available experimental data. We have also analyzed the modification of the transmission properties of bare opals induced by a sintering process. Our calculation predicts a linear decreasing of L-midgap frequency when the filling fraction decreases due to sintering, which is also in accordance with experiments. @S0163-1829~99!07239-2#