Silvering glass

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Updated: 2005-03-28 by HoloM (the god)
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John Pecora

Silvering glass

Post by John Pecora »

Has anyone tried to silver glass? I wonder how good it can be done at home for application and use as mirrors on the holographic table. Also, it might me something of interest if I fabricate a Single Beam Rainbow hologram in DCG. I could then "silverize" the back. I used to silver resist but we used a two part atomizing spray. That stuff is costy with the addition of the "Dual" spray nozzels. It is also messy because you are spraying a fine mist. The procedure below uses a method which is to pour the mixture on the glass and let is set.


http://www.make-stuff.com/formulas/mirrors.html
Dinesh

Silvering glass

Post by Dinesh »

It's a lot easier and cheaper just getting an ordinary mirror. Since a white light hologram is reconstructed in incoherent light, you don't need a front surface mirror. I just get a $0.50 mirror and glue it on the back. You can even use a mirror-like plastic, available at a local plastic store/manufacturer (MGM Plastics, San Marcos) which is even cheaper. Remember, however, that any reflection will diminish the incoming light. If you shoot at Brewsters, and therefore reconstruct at Brewster with incoherent, unpolarised light, the 'p' component of the light will vanish and the 's' component has a reflectivity of about 50%. This means that you'll reconstruct the hologram with 50% of the avaialble light just by reflection alone. If there's any absorption in the hologram itself, which there usually is, this absorption occurs twice with light going through the hologram to get to the mirror and then out through the hologram again. This could mean an additional 10% - 20% loss. The reason that transmissions, rainbows and achromats, are usually brighter than reflections is that transmissions use the entire spectrum. By cutting off 60% - 70% of the available light you severly restrict the possible brightness of the hologram.
Bruce

Silvering glass

Post by Bruce »

As long as it is a second surface and then can be sealed it would be fine (as in a traditional mirror), but a first surface would tarnish very quickly and then be unusable.
Bruce
Fred

Silvering glass

Post by Fred »

You can find some common methods here:

http://adsbit.harvard.edu/cgi-bin/nph-i ... ..23...13C

http://adsbit.harvard.edu/cgi-bin/nph-i ... SCREEN_GIF

For first surface mirrors the above Brashear process ist best.
Other mirrors are usually silvered by using the
Rochelle-salt-process.

To get a first surface mirror with constant thickness of the silver film
you shouldn't try spray techniques that are used only for industrial
silvering of household mirrors.

By the way: solutions that contain silver salts can produce silver
stains. Besides solutions that contain silver nitrate and ammonia
can form very explosive fulminating silver of Berthollet (probably
silver amide) if they dry. So it is necessary to add e.g.
nitric acid to the waste to prevent formation of fulminating silver.
Fred

Silvering glass

Post by Fred »

>Has anyone tried to silver glass? I wonder how good it can be done at home for
>application and use as mirrors on the holographic table.

I forgot to answer the above question:
I usually prefer the Brashear process (it uses glucose+fructose) for my first surface mirrors e.g. for my astronomical telescopes.
I gives very bright and hard silver films but the large amount of
silver powder that forms during silvering is a disadvantage of this
method.

Aluminizing is unfortunately very expensive in Europe now
(up to Euro 300 for a 12.5" mirror...). This is the reason
why more and more amateur astronomers are silvering mirrors.

Unfortunately all those methods produce much waste. Only a tiny fraction
of all silver is deposited so recycling it might be a good idea.

I also used the Lundin method (with Formaldehyd) for tests with first
surface mirrors but in my opinion it is inferior. The silver films
deposited by this process are softer and scratch easily.

Years ago I also used the Rochelle salt process (Rochelle salt is
used for reduction of silver here). It forms a reasonable silver
film but the solution must be warm for this method.

In principle you can get an excellent first surface mirror by using
the Brashear process but like all silver films without additional
layers they tarnish if they are used for first surface mirrors
within a few years.
But for your application the layer would be protected by glass and
paint so this would be no problem for you.
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