  We present herein a characterization of a standard method used at the High
Energy Accelerator Research Organization (KEK) to produce hydrophobic silica
aerogels and expand this method to obtain a wide range of refractive index (n =
1.006-1.14). We describe in detail the entire production process and explain
the methods used to measure the characteristic parameters of aerogels, namely
the refractive index, transmittance, and density. We use a small-angle X-ray
scattering (SAXS) technique to relate the transparency to the fine structure of
aerogels.
