Several aspects of quality control of the epoxy matrix may be conveniently investigated by means of Fourier transform infrared (FT-IR) spectroscopy. Difference spectra in particular can detect and define slow chemical reactions in the initial reactants as well as the presence and effect of water and other impurities. A least-squares curve-fitting procedure determines the composition of uncured and partially cured mixtures of the initial reactants. The degree of cure and differences in chemical processes occurring during various stages of the cross-linking reaction also can be studied by FT-IR methods.