This paper reports on a study of thermotropic liquid crystals (LC's) confined between two crystalline surfaces studied using the surface force balance technique. A quantitative approach based on measurements of the wavelength splitting (WS) of fringes of equal chromatic order was proposed, which allows the study of orientational transitions in LC films. Reasonable agreement was found between predicted and experimentally measured WS in moderately thick LC films. Optical properties of the LC's were studied experimentally for different orientations of the confining surfaces as a function of the film thickness, humidity, and duration of the experiment. It was shown that upon progressive confinement the medium-range forces in the layer noticeably increase when the twisting angle between confining surfaces increases. It was demonstrated that increase in humidity diminishes anchoring of the LC's to the surface.