The applications of thermodynamic theory to preferred orientations based on minimization of the Gibbs free energy is discussed in order to address the difficulties raised in recent work by Cardinale et al. [G. F. Cardinale et al., J. Vac. Sci. Technol. A 15, 196 (1997)]. We find that the preferred orientation of the cubic form of BN with the [111] direction lying in the stress plane is correctly described by the theory provided that the term linear in stress is included. We also describe how the predictions of this theory for the hexagonal forms of BN and for glassy carbon under compressive stress conditions are reconciled with measurement by allowing for reductions in the elastic constant s(44) caused by imperfections.