Spray Coat for mirror-like finish?


I have been trying using printed parts (Form 3) to mold PDMS (Sylgard 184). We would want optical-smooth surfaces and I mostly use 50um (25 um doesn’t really smooth the surface). I am seeking a polishing method that does not offset the surface too much (<20um I hope). The surfaces that need polishing are quite irregular and convex.

I tried sanding from 800 up to 3000 grit. That ended up still far away from mirror-like finish, but I was already seeing
some long-range bumps caused by inconsistent sandings from an initially macroscopically smooth surfaces, which discouraged me going up to 7000 and 10000 grit

Would plastic polish like Novus be a better alternative than sandings?

I would also like to try sprays or dip coating, but there’s just too many options and I have never seen two identical solutions after a lot of search. Is there a reliable solution that most people here trust?

I read the Formlabs lens making article which coats the lens in the same type of resin for multiple cycles. I am just afraid that it adds too much thickness , or even accumulates huge drops or chunks of resin at some corners due to
our surface profile.

Since we’ll be using it as a mold to cure PDMS, it’s best that this polishing coat happens to prevent curing inhibition.
Is there specific types of coating product to avoid because of this?