The interface geometry of Vycor porous glass was examined by adsorption of water in conjunction with small-angle scattering of X rays and neutrons. When the sample is dry, a fractal surface with a fractal dimension D similar to 2.5 was detected. When wet, a soft hydrogel is formed, resulting in a diffuse boundary. To observe a fractal surface, thorough drying of the sample is necessary, however. It was shown that a small amount of water, 3% w/w, is sufficient to render the surface smooth.