Quote Originally Posted by Gerald C Koch View Post
Fungus damage can be removed by using cerium oxide mixed with water as a polish. People make telescope mirrors all the time and the final step is polishing. Check the web for suppliers. As mentioned above the coating will have to be re-applied. When I was in graduate school I had to polish sodium chloride optical windows all the time. Only difference was using ethyl alcohol instead of water. (Sodium chloride transmits infra-red light while glass will not.)
I bought some Cerium Oxide last year when i bought new stocks of polishing grits. I had to make some Rollei focus screens for a Microcord & Rolleicord III and decided to give the Cerium Oxide a try after the #600 grit I normally use - the reults were the glss began to polish smooth losing the ground grain. The Lapidiary supplier I use had told me they mainly sold Cerium Oxide to telescope makers.