Epoxy resin, Union Carbide ERL-4206, is particularly suitable for vacuum impregnation of porous rocks. Viscosity and vapor pressure of liquid resin mix are low. Shrinkage upon polymerization is low. Polymerized resin is hard, clear, and insoluble. Index of refraction is near 1.54. Readily soluble red dyes are available to produce intense transparent color in thin sections. Such thin sections are used to prepare high contrast photomicrographs for the purpose of sharply distinguishing pores from clear grains.