[ARC5] WHINK and crystals - plate glass.

[J. Forster]

Your point is well taken.

Some people use a 'figure 8' pattern and rotate the plate frequently. Even
if the surface of the plate eventually does become a bit dished, the
curvature is over a much, much larger area than the crystal, so minor
dishing of the plate still looks locally flat to ther crystal.

It's mostly a matter ow how much is too much.

On a related topic, I was just at a Michaels Craft Shop. They have several
things for glass etching. There is an etching cream. I( think the stuff
could be made into a water solution and used for xcrystal etching. The
brand was something like Armor or Armour. A few ounce bottle was about
$12. It was an ammonia-flourine compound. If you are interested, Michaels
has a web site.

-John

==============





> On 28 Jun 2013 at 9:19, J. Forster wrote:
>
>> Optical flats, used w/ LASERs are probably a whole lot flatter. They
>> are often good to 1/100th of a wavelength of roughly 500 nM light, or
>> 5 nM.
>>
>> They are pretty expensive though. Think $300 for a 1" OD, 1" thick
>> one.
>>
>> You can sometimes be picked up cheap on eBay.
>
> One thing that has always confused me, and which has held me back from
> attempting to grind crystals to frequency on a piece of "plate glass" is
> that it
> would seem to me that the glass would not remain "perfectly flat" for very
> long, since the same grinding compound that works on the crystals would
> most certainly also work on the glass at the same time and to the same
> extent.
>
> Might anyone here have any comments to add or corrections to my way of
> thinking about this? Please?
>
> Ken Gordon W7EKB
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