hi Fritz I thought there might be a music connection there some where - wasn.t sure about the name of the cleft you use as a logo I am a rather poor piano player as an English comedian remarked " all the right notes but not necessarily in the right order") and our music tends to have only the treble and Base cleft.It sounds like we have had very similar careers but on opposite sides of the Atlantic, but I did spend some time doing research in Boston and living in Concord MA.On the question of Aspherical mirrors a few years ago we did quite a bit of work on metalizing mirrors for automotive prototypes which had been produced by 3d printing. The main problem we encountered was build lines including slight layer shifts and surface texture. To cut a long story short we found that sanding and painting then sanding some more was very laborious. In the end with the aid of a polyester resin manufacturer we developed a special spray coating with a very small "shrink back" and ease of sanding. Though the quality of 3D printing has greatly improved we still use this process.Taking a automobile head lamp as an example the process consists of using conventional spray painting techniques to "bury" the surface texture the applying, again spray painting, an extremely thin film of an epoxy resin on the surface of the mirror.Once the epoxy is fully cured using a water based process similar to the traditional way of silvering say bathroom mirrors we deposit a reflective silver film which we then passivate with Tin to reduce tarnishing.