Anyone know where to buy semi-silvered glass?

Inexpensive if you can find what you need:

I have several long, narrow pieces from junk xerographic copy machines. I don't know what function they played. They probably would not help your situation. I think they are about 1/4 inch thick, 1/2 inch wide, on the silvered side, and probably 12 inches long.

Paul

Thanks for the offer, but the thickest glass which will fit in the frame is 1/64" thick.

Best wishes,

Chris

Thanks for those links. I took the reflector frame out of the microscope today and measured it. Looks like the piece of glass needs to be 1" in diameter and 1/64" thick, though a thinner piece could possibly be used.

According to some articles I've found online, certain metallurgical microscopes use a plain glass sheet which works by total internal reflection rather than a semi-silvered mirror. If that's the case with my microscope, it would make the glass much easier to find. I might even be able to use a circular glass cover slip.

Then there's the problem of fitting the spring clip over such a thin piece of glass without breaking it. I figure I should order several pieces of glass!

Best wishes,

Chris

The modern way of making semi-silvered mirrors is by vacuum evaporation. You need a really good vacuum pump, some large diameter stainless steel plumbing with flange couplings and knife-edges which bite into copper washers -- replace the washer after every use.

Once you pump down to a low enough vacuum (the roughing pump gets you most of the way, then you go to something like a "sorbtion" pump or a turbo pump, or oil diffusion pump), then you put high current through a filament around which is wrapped the metal which you wish to deposit -- like perhaps aluminum wire. This boils off the metal, and deposits it on the glass. You can control the thickness (and thus the opaqueness) by timing, or the better way is with a crystal oscillator, with one side of the crystal exposed adjacent to the glass being coated. You can determine how thick the coating is by the change in frequency of the oscillator from zeroing it before you start the plating.

Obviously -- this is a lot of stuff to do at home -- but you may be able to find someone who retired from doing such work and is continuing to play with it at home.

I don't know where you live, but it could be a possible choice. Hmm ... if you are near someplace with a college which does Scientific work, you might be able to find someone there to help you. Obviously -- cut the glass to shape *first*, and then coat it. The real trick is coming up with a way to hold it down during plating without blocking more than a bare minimum of the area -- say three tiny fingers just barely sticking over the edge. And the whole fixture should be metal, no plastics in the high vacuum.

Good Luck, DoN.

Or even try cutting some 0.015 Mylar sheet (overhead transparencies) with scissors. Not really optically flat, but maybe worth experimenting with.

Might not be what your looking for but take a look at some of the replacement side mirror items at your local parts store. The Help mirror I just bought is a strange item. You can hold it to a light source and see through it, Put it against a backer material and it becomes a good mirror. It was a simple rectangular mirror for replacing the older style GM truck mirrors. Thickness wise it is maybe an 1/8"

Maybe they can send you the replacement mirror. Bob

Did you check Edmund Scientific - the Optics catalog? They have optical quality lenses and mirrors.

Thanks. That was a fascinating read. I have a small two-stage mechanical vacuum pump. I was also offered an oil diffusion pump a while back, and I suspect the offer is still open. But it does seem a great deal of work when I hadn't intended the microscope to be a project in itself!

Best wishes,

Chris

I had wondered about this, but like you I was concerned about the flexibility of the sheet. It might not matter, as the sheet only reflects the illuminating light, not the image, but I'd prefer to do a good job.

Best wishes,

Chris

That reminds me. CD-Rs look semi-silvered in bright light, don't they? But I suspect they're a bit too opaque.

Best wishes,

Chris

How about a reflective ND filter? Edmond Scientific has them. I think I might have some laying around. Send me an email at t miller @ u maryland . edu. (remove the spaces)

Tom

Make up some Tollens reagent (ammoniacal silver nitrate) and use a bit of glucose solution to set it off.

Mark Rand RTFM

I'm not too keen on this idea. I'm wanting a working microscope rather than a time-consuming project.

Best wishes,

Chris

I can understand that -- but I figured that you should know what is actually involved so you could decide for yourself. Since there was a lot of this being done in an Army R&D lab where I used to work, I got to learn how it was done, although I never did it myself. But I always like to learn how anything is done, so I kept my eyes open.

For that matter -- the older copies of The CRC _Handbook of Chemistry and Physics_ used to have a lab tricks section which included two or three ways to silver mirrors. Those were mostly chemical approaches, not high vacuum deposition.

Just ask yer dentist for one of those disposable inspection mirrors. Remove the mirror from the plastic housing/handle. Insert in microscope holder. Done.

technomaNge

On Thu, 21 Feb 2008 10:11:57 -0800 (PST), Christopher Tidy wrote as underneath my scribble :

I had a microscope with a ~45 deg semisilvered mirror that needed replacement, tried a standard mirror but turned out it was a "cold mirror" and removed IR from the lightpath to save IR from the users eyes (multicoated so IR passes straight through). Be good idea to find out the original specification....!? C+

Are they semi-silvered?

Many thanks,

Chris