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Silver mirroring puddles on glass, oxidizes at the edges

Q. Hi all, first off thank you for a very informative site, and apologies if this has already been covered but I couldn't seem to find the answer.

We are pouring puddles of silver nitrate (well, reduced Tollen's reagent) onto glass, to get a puddle mirror shape.
Some have worked brilliantly and crisp, but many have intense yellow/brownish oxidation colours at the edges where the silver is quite thin (somewhat transparent still).

Some extra context:
I am preparing a 0.1 M solution of silver nitrate solution, 0.8 M solution of potassium hydroxide, and then 0.244 M glucose solution.
Per unit silver nitrate, I add ammonia until clear, then about 30% KOH, again ammonia until clear, and then 8% glucose as the reducing.

It seemed initially that the problem was the puddle was 'traveling' after the reaction had initiated, resulting in less active solution moving onto other parts of the glass and oxidizing. This is true, but now we have it perfectly leveled.
We have noticed two things:

1) The liquid, after reacting for a minute or two, will clear up on the glass as silver deposits and appears to lower its surface tension or viscosity and will suddenly spill over the puddle (and big nasty yellow).
2) there is yellowing at the edges still, and sometimes these horrible "drips" from rinsing where a yellow drip line appears across the mirror. This seems to also happen if we rinse too early (in the hopes to avoid that spilling over). So a bit of a pickle; cannot rinse early, but if we don't rinse early, we get big yellows at the edges.

Some things that seemed to help:
• Slowing the reaction down by cooling the solutions seemed to help.
• Playing with the KOH amounts I add. Initially I was at 50% to silver nitrate, but I've brought this down to 30% hoping this would help (and because it was turning the silver nitrate nearly black, which seems to be too aggressive as I've read it should be brown at the Tollens reagent stage) but I am not so sure.
• Ensuring no puddle movement (but as mentioned, the liquid travels suddenly when clear).
• I tried introducing a little bit of diluted sodium sulfide and even liver of sulfur to encourage the yellows to stay dark (better aesthetically) but this made everything go wonky, so I abandoned. I also tried applying it afterwards onto the mirror surface but this messed it up bad.

Any ideas on how to get a crisper edge? Or to make sure those yellows are darker without ruining the mirror itself?

Kevin Rouff
- Amsterdam, NL
September 5, 2024