[Satchmo]

Alex, the 18 inch conicals may be just held down to the cell with blobs of silicone just like any other Chinese mirror . Conicals are about fast cooling.and convenience of mounting.Ive never seen one any lighter than a standard 1.6 inch plano blank in the same size and conicals usually quite thick in the middle.

Nick, theres no issue removing overcoated coating from a mirror as long as it borosilicate. Coaters have to tread more carefully working with softer glasses, removing the coating requires more care and patience but it can be done. .It does require a breif scrub with a felt pad to break through the overcoating, which doesnt harm the optical surface before the mirror is soaked. (It is easy to see when the overcoat breaks up from the appearance of the aluminium coating. If the coating is allready breaking down due to age this step is not necessary. I have cleaned off coatings many times without harming the optical surface and thats been verified with optical testing.