188-cm Reflector Telescope Realmuminization Project 

I think it is not polishing rather than chemical degreasing. It sholdn't make anything to the surface.

Yeah, it's less about polishing and more about deep cleaning...

Yeah looks nutballs to me too. The video says "backing soda". Not sure that's a thing. But, if you think about it, soda can be ground and screened as fine as cerium oxide.

Nonya Damnbusiness normally you use an acid - often ferric chloride - to remove the aluminum, and then baking soda to neutralize the acid.

concave

SiO (Quartz)- protection layer

Big professional telescopes like this one usually don't receive an overcoat, because they are realuminized once every 2 years or more often.

If there is no overcoating, then there is, NOTHING stops the aluminum from oxidizing. Al2O3 forms, which is hard and transparent.

Transporting the mirror off-site is not that simple. It's fragile, it's heavy, it's expensive and while it's away, the telescope is out of action. Transporting the vacuum chamber would be much cheaper to do. And even if the chamber stays on site, it doesn't incur costs in storage. The process doesn't change the figure of the mirror surface, so why would it need to be checked?

I have a feeling that they've looked at costs/risks and know whether the lens needs to have its figure checked. Since they're literally experts.

Huh? It is normal to realuminize surface each year. Aluminium simply reacts with stuff in air and it accumulates dust, dirt, oils from the air, etc. Even if it was made of gold it would need cleaning and resurfacing. As of the baking soda thing, I find it weird, but it is mostly not to polish the mirror, but to neutralize the chemical used for etching. In fact it would be probably better to use liquid solution for this, then a lot of soppy water, and then clean deionized water, and simply let it dry (or use a solvent as a last cleaning process), before realuminization. Polishing a mirror without checking it parameters is weird.