To be honest, the technical discussion is a bit beyond me. I can build any kind of mirror cell needed to support the mirror. Is it worth having it tested or refigured or should I just put it aside and move on?
Good point! The mirror is probably worth what you paid for it.
Having Cary evaluate and address the figure and coating seems entirely worthwhile. Building an entire telescope around an unknown, preexisting mirror is a risk of time and money... and this one (at the moment) has a three strikes against it: poor pedigree/history of similars, very thin, many negative disinterested testimonials. One common, reliable approach is to build the entire scope and just try it, as-is!
> If it works to your satisfaction --- enjoy it!
> If it's terrible, send it to Cary for evaluation.
- if Cary finds the substrate workable, ask him to refigure and recoat, as needed.
- if he deems it unworkable, ask him to make a (thicker) replacement mirror that will fit your scope.
It's more ideal to build a telescope around a known good mirror. At work, we occasionally took delivery of customer (meter-class) mirrors with mounts that were "almost finished, just needs a little tweaking", only to discover fatal flaws. Big, thin mirrors were notorious for that. Bad figure and terribly squirrely mount, stressed substrate... essentially nothing of value there, other than wistful hope. If the original shop went ultra-thin plate glass... just to save $$$ on the substrate cost... you can ~figure~ the whole process was --- cheap! To paraphrase Stephen Gosson (1579) "...you can't make a silk purse of a sow's ear". Tom