A few days ago, we silvered an 8” diameter 43” FL mirror that had previously been aluminized, and applied the Angel Guard coating.
We did a Ronchi test and some Foucault-Couder knife edge tests before stripping the aluminum and after the silver was applied.
To my amazement, we found that the mirror’s figure was about the same in both cases. How that works, especially how the Angel Guard coating is laid down so even and smooth over the entire mirror, is beyond me. But it DOES work.
Prior figure (aluminized mirror), seen with Ronchi grating of 100 lines per inch: https://share.icloud.com/photos/0LyqGC35cx0QfWKcd08aI0vzw…
Final figure (silvered mirror), with same Ronchi grating:
https://share.icloud.com/photos/03mdTeZD3dZ-bqGNoDZXSqpjw…
This is a video of us washing off the Angel Guard coating.
Here is a video of the finished mirror after drying. Notice that the very edge of this mirror did not take the silver coating, but the area uncoated is probably on the order of one or two percent of the total area.
Guy's Math & Astro Blog 
Guy – is this silvering process using the kit that you had last year? I recall the silvering kits were expensive.
J Texereaux has a procedure for silvering, in his book Chapter XIII-5 using a 4 part set of solutions of silver nitrate, ammonium nitrate, potassium hydroxide, and sugar+tartaric acid, referred to as the Martin process.
Mordanting with stannous chloride is another pre-step in the J.T. procedure. It seemed like a good bit of chemistry and I can see why the kits would be attractive compared to the French cuisine method!
Best to you and Alan, fun project ! Ben
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Yes, it’s the very same kit we were donated last year right before the pandemic. The kit is several hundred dollars but will do dozens if not hundreds of mirrors. According to the safety data sheets that are obligatory with items like this, there was no ammonium nitrate, no sugar, and no tartaric acid.
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