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Hi Frank,
I should perhaps be considered as “fixing” sextants rather than restoring them but I’ve tried two methods of “resilvering” mirrors.

20(?) years ago I read of someone’s emergency fix of painting the back of a mirror with black paint. I have not been able to find that reference lately but I tried it, it’s easy, and it works well for the sun. It was on an old sextant with tiny mirrors and I had problems finding stars. I didn’t keep that mirror and started buying thick first surface and second surface mirrors from surplus companies and cutting my own, square, mirrors.
Cutting glass is not too hard but I had several that broke the wrong way. I bought some cheap glazier’s tools that make the job much easier. Photo, from right, of glass cutter, slightly curved-jaw breaker, and end-holding nippers.

I bought a Cassens & Plath sextant that needed legs and a round horizon mirror resilvering. I decided to try the Mercury/Tinfoil amalgam on the Bill Morris site.

https://sextantbook.com/?s=Mercury+

It works. My first try didn’t because I overlooked the step of backing the amalgam up with paper for release purposes. The film came apart when I separated the two pieces of glass. My second try of mirror, amalgam, paper, glass worked pretty well. I have two small defects visible at about 4 o’clock, a small fuzzy area about 1 o’clock, and an imperfect paint edge across the center of the mirror. It looks good at first glance and is completely usable.

I bought a diamond edged hole saw but the surplus supply of thick mirrors seems to have dried up so I’m not ready to try cutting a round mirror yet.
Regards, Noell

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