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/spraysilveringtelescopemirro

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/home/how-to-spray-silver-a-telescope-mirror 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.