Following the sanding operation, the lenses are polished on an identical machine, except that felt polishing pads washed with polishing compound are used instead of sandpaper and water. When this step is completed, the lens is optically clear without visible scratches. A cylinder machine, left, can sand two lenses at the same time. Air pressure holds the lens and the sanding block together, and a timer switches the machine off at a preselected time. After sanding, the lenses are polished, right, so they are perfectly clear without any scratches.
Liquid polish flows over the lenses and into a reservoir to be recirculated.
Sometimes special coatings may be applied to the lens. At this point the lens blank has had additional curves ground in the back of the lens and it has been polished. However, the large diameter blank still has to be sized and shaped to fit into the frame selected by the patient. Several methods are used, depending on the equipment, but they are all based on the following description. The lens is mounted into an edger.