Gold Versus Aluminum Surfaces in Telescopes

Low maintenance? No tarnish as with silver, or would that too use a protective coating? There might also be some gain in its value as a classic antique. (Just guessing.)

Having made telepscope front surface mirrors the old silver way, one wonders why not do the same to make a silver coated mirror. Of course, it will tarnish in a few year and in 20 years if you use a sulfur scavenger and a sealed housing with a clear entry glass with an anti reflection coating.

reduction of silver is cheap and easy to do on a 6"

this tells all, read a few

http://www.google.ca/#hl=en&source=hp&q=%22mirror+making%22+%2Bsilver+%2Breduction&btnG=Google+Search&aq=f&aqi=&aql=&oq=%22mirror+making%22+%2Bsilver+%2Breduction&gs_rfai=&fp=1312a4e138347d6d

I seem to remember from many years ago that gold is a superior reflector for IR wavelengths. Since planets are cold compared to stars, proportionally more of their energy is in the IR region. If this is all true, then a gold mirror should produce a slightly brighter image for planets, if the sensor (your eyes?) can detect IR or nearby wavelengths.

Sir,

We are in India and serving to Space agency here. We coat gold. Could you send it to India? We need to know 1) Thickness of The mirror.2) Is it Glass or Quartz

3) What is the shape of the mirror? convex ,concave

4) Which surface to be coated.

5) Could you clean the mirror before sending?( remove coating)

6) We will coat it at a reasonable price. However Please consider the transportation cost

krnawathe@litelir.com

0091-9422030167

Where in the world are you located? We have a microelectronics fab on campus at RIT, perhaps one of the students could do the job over the summer? I'm not sure that this is possible but, if you are interested, I will check. I'm sure you would have to provide or pay for materials. Beyond that I don't know. Can't hurt to ask.

I've known Jeff Decker at Majestic coatings for ten years, He does all my optical coatings including AR for my lenses. It was he who said I could coat the mirror for $450 and added that I'd have the whole deposition chamber to myself as no one does it any more. I figured it out: it's NOT the cost of the gold, it's the process.

Some have speculated that the mirror is not the original but an orphan from an IR spectrometer. Others cautioned that coating with gold requires a precoat to insure the gold adheres. If it is an IR mirror than there is the chance the mirror's figure is not as good as one designed for the higher frequencies of the visible spectrum. I'll be testing the mirror soon so some of these questions may get answered.

It will get an aluminum coating and the customary protective overlay, at Majestic, after I test it.

Thanks all for the responses.

L.J.

I will not spend $450 in the interest of maintaining an antique's

Sir,

The gold is the best reflector (99% for pure gold)for the range of Electromagnetic radiation Spectrum under consideration.

gold retains the reflectivity for a very long time, as it does not oxidise.

kiran