Mirror grinding is a precise and patient process used to turn a rough glass blank into a highly accurate optical surface. It is the foundation of many optical instruments, especially reflecting telescopes. The goal is to shape the glass into the correct curvature and then refine the surface until it is smooth and accurate at a microscopic level.The work usually begins with a flat, circular glass blank and a tool, often made of glass or ceramic. Abrasive powders mixed with water are placed between the blank and the tool. By moving one against the other in controlled patterns, material is slowly removed from the glass. Coarse grits are used first to establish the basic curvature, then progressively finer grits smooth the surface.During rough grinding, the mirror worker focuses on creating the desired radius of curvature. The classic motion is a repeated “W” or circular stroke, with the mirror and tool frequently rotated in opposite directions. This helps prevent unwanted shapes and keeps the surface symmetrical. At this stage, grinding marks are clearly visible, and the surface is far from reflective.Once the correct curvature is reached, the process moves to fine grinding. Finer abrasives are used, and each step reduces the size of the microscopic pits left in the glass. Careful cleaning between grits is essential to avoid contamination from coarser particles, which can scratch the surface. By the end of fine grinding, the mirror appears uniformly frosted and feels very smooth to the touch.Polishing follows, using a pitch lap instead of a hard tool, together with a polishing compound such as cerium oxide. The pitch conforms slightly to the glass surface, allowing the optical figure to be refined. Polishing removes the last traces of roughness and gradually produces a shiny, reflective surface. This is a slow stage, requiring consistent strokes and regular inspection.The final and most delicate step is figuring, where tiny amounts of glass are removed to achieve the exact optical shape, often a paraboloid for a telescope mirror. Specialized tests, such as knife-edge tests or interferometric methods, reveal minute deviations from the ideal curve. Based on these tests, the worker adjusts stroke patterns and pressure to correct high and low areas.Mirror grinding demands concentration, careful measurement, and an understanding of how each motion affects the glass. It is both a technical and an artistic craft, transforming a simple piece of glass into a precise optical component capable of capturing sharp images from distant objects.