These glass bodies are light weight porous structures such as a boules of high purity fused silica or ultra-low expansion glass. More specifically, the porous structures are supports for mirror blanks. Porous glass is made utilizing flame deposition of pure silica or doped silica in a manner similar to the production of high purity fused silica. Bubbles or seeds are formed in the glass during laydown. Several means of creating and controlling these seeds are available. The processes use incomplete combustion to create the bubbles. There are a number of different steps to create the incomplete combustion. One such step is a short distance between the hydrolysis flame and the glass precursor.
