Just don’t use an aluminum vessel…
It works with molten glass from several articles
Since the 1980s, the University of Arizona’s Mirror Lab has been casting glass mirrors in rotating furnaces, which are now capable of casting monolithic mirrors as large as 8.4 metres. Gravity and centrifugal force does most of the work forming the figure on the mirror, which drastically reduces the amount of grinding needed to produce the final mirror.
This is different from the liquid metal mirror, in that the spin forming is just during the initial casting phase. After that, it is a conventional glass mirror which holds its figure due to its internal strength.
Thanks! I haven’t paid much attention to telescope mirrors since having a mirror-grinding office mate a long time ago. Jack’s was much smaller than 8.4 meters, he eventually finished and built a small observatory in his back yard for the telescope using it. I don’t remember many more details, and he sadly passed away a few years ago.