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Changes observed in polarized light transmission through an anisotropic material, such as birefringent porous glass, upon contact with air bearing vapors of volatile organic compounds serve as the basis for a very sensitive broadband chemical sensor. When properly designed, vapor sensors based on such porous glasses show changes in transmitted light intensity or spectral content (color) detectable by eye. When placed between two crossed polarizers, the form-birefringent porous glass produces an observable phase shift that undergoes a readily detectable decrease upon exposure to all organic vapors we tested thus far. The optical effects resulting from exposure to vapors are reversible and believed to result from capillary condensation of solvent vapors and attendant reduction of anisotropy. A good control of the microporous structure as well of the surface chemistry offers flexibility for tuning the sensor response to VOC industrial applications. Simple sensor miniaturization with low cost materials is possible.