From: "Jerry" 
To: "'Vladimir Galogaza'" ,
"'ATM shore'"
        
Reply-To: "Jerry" 




-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net] On Behalf Of Vladimir
Galogaza
Sent: Thursday, August 21, 2003 8:13 AM To: ATM shore
Subject: Re: ATM some questions/ideas


Frank,

>and during this time the luster on the surface increased at least
50% with the black rouge,
I wander how you can tell.
Recently I posted question about quantitative evaluation of the
 polish quality. I received not a single answer.

While  I polished my mirror, at certain stage I could not decide if there
was any more progress.
Intensity of stray light of focused sun image or laser spot as a measure (
indication) for good polish reached certain low level and I could not see
any improvement in this test. Recently I have seen several  posts
advocating continuation of polishing for good measure, even after usual
criteria were met. How professionals do it?
Hints appreciated.

Vladimir.


**********************
Vladimir....

        Your question is not to me but let me say something of my
experience. I also noted that you asked about "quantitative
measure". And William Cook asked whether any one had used "phase
contrast" test. And James Lerch wrote of the great polish of the
Zambuto mirror. And then Frank wrote of "luster" using black
rouge if I remember correctly.  I did not answer you because my thoughts
are not "quantitative". And I was not sure whether the question
is "when is polishing done?" or "how can you tell if the
surface is smooth at the micro level on a fully polished surface?" And
then the word " "quantitative" throws me off a little.
Polish seems to me to be a "yes or no" as to whether polishing is
finished or not. To put a more precise quantity on it might be difficult.
And I think of smoothness as part of figuring.


        Taking all the related posts together I think I know how best to
answer your question. I think that all of the posts are not actually
referring to the same thing. I think there are two parts to the topic.
"Fully polished" and "fully polished and smooth".

        There is a point when the surface is fully polished. And then there
is a subset of "fully polished" that is smoother than just fully
polished. If you have polished out all of the irregularities of the surface
that are the result of grinding, you have "fully polished" the
surface. You still have a surface texture at some scale. Dog biscuit is an
example of a condition that you can have on a fully polished surface. It is
a roughness that is polished in. And you can carry this idea down to a
smaller scale to and beyond the point where the roughness is so fine that
it cannot be seen directly under the Foucault test. I say Foucault because
that is what I think most use in one form or another.


        I do much the same as everyone else to decide when I have fully
polished. I look with my eyeball and magnifier under various lighting
conditions. If I can move the specks I see with my finger they are
"on" the surface. If they don't move they are "in" the
surface and I am not done polishing. And then I might add a little work
just for good measure. What is another hour compared to the entire job. I
wouldn't do 50% more until someone can show me that I have failed to polish
previous mirrors. Keep in mind that as you polish you can see the area that
is polishing slowest. It is usually the edge. When the surface becomes
clear that is obviously the place to look the hardest when deciding if you
are finished polishing. I go until I can see no greyness and just a bit
more for good measure.


        It seems to me that you can't totally separate "fully
polished" from
"smooth and fully polished" You might say that if it isn't smooth
it isn't fully polished. But you can have smooth and then polish it away.
It doesn't take long to go from fully polished with a rough dog biscuit
like surface to fully polished and smooth. And it doesn't take long to
polish dog biscuit back in. I think micro-ripple is the term for the
smaller scale roughness. I'm sure someone will correct me if I am wrong on
that.

        I have my techniques for getting the surface "smooth". And that is
what I think James is seeing on the Zambuto mirror. It is not really
because Zambuto polishes extra long but because he smoothes the polished
surface extra well. And the same for the "luster" that Frank
speaks of getting with the black rouge.

        You can smooth a mirror beyond just the point where you can directly
see roughness on the surface and tell that you have. (I say that with
certainty to give the nay sayers an opening.) I don't know if Frank meant
seeing a luster by looking at the surface with a magnifier or under the
Foucault test. But for me, under the Foucault test I can see a brightening
if I continue to smooth the surface after the point of ridding the surface
of roughness I can actually see directly under Foucault test.

        I intend to do something like the phase contrast test mentioned by
Mr. Cook on my next mirror to see if the brightening I see is really
directly related to surface roughness that is too small to be seen as
roughness.



Jerry

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