In article ,
Chris Wells wrote:

Could be worse, we could still be using electrum or speculum metal to
make mirrors.

Or using large vats of mercury.

Actually, I think someone is doing just that.

A pool of mercury is spun up to form a curved surface, used as the
mirror for, I think, a solar telescope.

Lessee... Ah:

http://www.astro.ubc.ca/LMT/lm/index.html

The focal length is dependent on the rate of spin. Kewl.

The first ones were made in 1872, there are more modern ones in use now,
running up to 3m in diameter. Turns out to be several "someones", and
plans for more are being considered. Even proposals for putting some on
the moon.

Hold your breath in the observatory...