[alexbock]

I made several attempts at acetone vapor smoothing on mirrors printed in ABS and ASA and the surfaces always came out very well polished at the micrometer scale but unacceptably warped, wrinkled, or patterned at the millimeter scale. The best finish I've gotten on a 3D-printed mirror was from sanding and polishing with a cotton ball soaked in cerium oxide slurry while the mirror blank spins on a pottery wheel.

Chemically depositing silver with the old-fashioned immersion setup is also very tricky as the reaction is quite temperamental. I recommend the two-part spray process if you want to try silvering a telescope mirror.

[geokon]

Oh very cool that you tried it. Shame it didn't work out, but I guess that all kinda makes sense.

just out of curiosity what's the "two-part spray process"?

[alexbock]

I originally heard about it from this page written by a group who silvered a 28-inch mirror this way: https://sites.google.com/site/spraysilveringtelescopemirrors...

It's still ultimately a silver nitrate reduction reaction, but it's extremely consistent. I tried reproducing the classic silver nitrate/glucose/sodium hydroxide/ammonia silvering baths astronomers used before the modern switch to aluminum vacuum coatings, and my success rate was only about one in five attempts. It's much more difficult to execute than the typical silver nitrate demonstrations where someone silvers the inside of a glass flask because you need the silver to produce a perfectly even layer on the outside surface of the glass for a telescope. The spray reaction has worked for me every time.