Who does prism aluminizing?

[John Schneider]

I have some old (WWII binocular) prisms on which the silvering is corroding. I'd like to find a place that will strip off the silver (HNO3 works well I believe) and then vacuum deposit aluminum. I haven't heard back from John at Focal Point; are there any telescope suppliers etc. that do this?

Conversely, does anybody have a DIY protocol for doing this? I can get access to a wet lab and I think I still know somebody in the SEM lab who would operate the vacuum-deposition machine for me (in which case I could use aluminum, silver, gold, etc.).

[Nathan Potter]

John, this is often a double deposition process where a few hundred angstroms of chrome is needed as an adhesion layer for aluminum or silver. The reflecting aluminum or silver layer is then deposited in the same vacuum system to a thickness of 2000 angstroms or more. For reliability of coating lifetime a very thin layer of silicon dioxide may be applied to the top, final surface.

You can cheat and get away with just the reflective coating if the final film is not exposed to the elements. Google for current suppliers. I used Thin Films Inc. somewhere in silicon valley in the past. Vacuum deposition is expensive especially the bi or tri layer sequence.

Nate Potter, Austin TX.

[Harold_4074]

You might consider looking into the amateur astronomy community. Telescope mirrors are (used to be?) commonly homemade, and aluminized rather than silvered by the old Brashear process (which you could also consider if you are chemically inclined).

On properly cleaned glass, no undercoat is normally needed for aluminum deposition, as it would be for, say, gold. An overcoat is desirable, but your silver coatings were probably just lacquered, and you could do that on aluminum for scratch protection.