Someone (a coater) told me to use the etching solution found at Radio Shack. I haven't tried it myself. Also, I have a friend who makes the mirrors for Questars and the Quantums when they were in business. A Quantum owner sent in a 6" version that had been in a fire. The mirror was washed up and recoated. The meniscus corrector was shot however and had to be replaced. The company replaced the whole unit gratis.