Before revision: ITT Corporation - Ion Figuring This is particularly useful in the manufacture of segmented mirrors, since the shape of the optics can be maintained correctly all the way to the edge of the aperture, whilst mechanical polishing techniques tend to have trouble with distortion of the polishing tool when it overhangs the edge.
After revision: This is particularly useful in the manufacture of segmented mirrors, since the shape of the optics can be maintained correctly all the way to the edge of the aperture, whilst mechanical polishing techniques tend to have trouble with distortion of the polishing tool when it overhangs the edge.