From: Guy Brandenburg 
To: "Jerry B. Hillman" 
CC:  atm{at}shore.net
Reply-To: Guy Brandenburg 


Jerry,

Sorry about your glass.

To see the fringes all you need is an ordinary fluorescent light bulb (or
tube) of some convenient size and a piece of colored translucent plastic
that will filter out all but one of the primary emission lines that the
fluorescent light bulb emits. The green line or the purple line look good
and strong to me. If you can get a sheet of diffraction grating and you
look at a fluorescent light bulb, as opposed to an incandescent light bulb,
you will see those colors distinctly. Find a place that sells sheets of
colored plastic (translucent, so as to make the light source diffuse) and
find one that matches the line (or color) that you choose.

The red line sort of looks good to me, and is extremely bright, but I fear
that there might be a number of other lines very close to it that would
mess up the monochromatic effect. I can't really tell, though, whether
those other lines next to the red line are real or are artifacts of my
not-so-fantastic diffraction gizmo and my eyes.

David Gordon made a really neat fringe viewer out of even simpler
materials. (As far as I know, he thought up the idea himself.) He took a
compact fluorescent light bulb, some green crepe paper, a large cardboard
box, a light bulb holder, and a sheet of plexiglass. He cut the top and
most of the front out of the box, installed the plexiglass sheet at a
45-degree angle, and put the light bulb at the top, with the green crepe
paper between it and the plexiglass sheet. He blackened all of the interior
parts of the cardboard box. To view the fringes, you look at the reflection
in the plexiglass, after laying the reference flat on top of the flat you
are trying to test, VERY carefully. It is not necessary to put the little
wedges of paper - nature gives you
'wedgies' naturally. It works best if neither surface is aluminized. If
either surface is aluminized, the reflection almost totally overwhelms the fringes.

Once you have a monochromatic light source as described, then when you lay
the reference flat on the flat you are testing, you will immediately see
the fringes.

-      &&&        -     &&&& is the flourescent light
|                  |
|*****************/   **** is the crepe paper
|               /
|             /     / is the plexiglass - any glass will do;
|           /         it acts as a 2-way mirror, letting
|         /           through the filtered light and also
|       /             letting you see the tested pieces
|     /                from above, as it were
|   /
| /
|       ^^^^^^       ^^^ is the tested flats
-------------------    ---- is the bottom of the cardboard box.

Pretty neat & simple, hey?

Guy B

Jerry B. Hillman wrote:
> Hi all,
> Now that I have wreaked this piece of glass I guess I buy a diamond blade
> for my saw and try to salvage enough from the pieces to make a secondary.
> How do I prevent the water for cooling from destroying my circular saw, or
> do I need a special saw for this also? And how do I get the water where I
> want it?

If I were you, I would NOT use an ordinary circular saw. Don't risk
electrocuting yourself or destroying the bushings. I would go to either one
of those huge hardware stores or a place that specializes in ceramic tile
and I would RENT, not buy, a saw that is designed specially for cutting
ceramic tiles. I think they usually come with water cooling thingies.
Remember that you really, really don't want to breathe glass dust.

> Can anyone clue me into the technique of interference testing using modern
> techniques. I tried Texereau's method and didn't see anything. No fringes,
> nothin. But then I don't have either a mercury lamp or a neon glow tube.
> What should I be using?
> I am a little depressed right now about this.
> Clear skies, Jerry
>
> BTW - Cutting thick glass isn't the same as cutting normal window plate
> glass.
>
>
>
>

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