[ATM] Cu3Sn Progress

[gfbrandenburg at yahoo.com (Guy Brandenburg)]

Anthony,

Interesting experiment. As long as you are
re-inventing the wheel and entering the
Rocky-and-Bullwinkle Wayback Machine, it might be
instructive to cast a glance at one of Leon Foucault's
methods when he first invented the modern method of
making silvered glass blanks. He used a *paper* lap,
which he glued to the tool, and then used something to
raise the nap on the paper and he polished with the
lap being ***dry*** and using powdered rouge. 

My translation of the relevant passages follows:

"We are acquainted with several methods for polishing
glass, but the one that appears to us to be the best
for working on mirrors is the method of polishing with
paper laps  and English rouge. On the very surface of
the disk which served as tool for the mirror, we use
starch to glue a piece of paper whose weft appears as
uniform as possible. By using a sort of glass meniscus
known as a "colloir", we push the excess starch
towards the edges of the glass, and we apply the paper
completely and fully onto the tool surface. Then, by
rubbing the glass with a damp sponge, we detach the
little particles of paper, and we strip or roughen the
paper in such a way as to raise a velvet-like nap
which, once dried, will be effective at holding the
polishing powder. We must still rub the paper with
pumice, then chase it with a brush, after which we
apply the English rouge with a scrap of crumpled
paper. Now the polishing lap is ready. The mirror,
having been washed and dried, is placed on this lap,
which touches it all over and will make the finish
clear up after the very first few strokes. But before
putting the mirror into motion, it is necessary to
support a part of its weight by attaching it again to
the suspension spring and by using a cord that is
stretched sufficiently tight. This arrangement also
has the benefit of allowing us to move a rather large
mass without too much effort. But what is more
important is that by reducing the pressure upon the
polishing lap, we slow down the creation of heat due
to the friction of polishing, and we avoid to a
certain extent the deformations that would result from
that heat."


I have no idea if this is how Herschel and the
servants of Lord Rosse polished their speculum
mirrors. However, if you want to use modern methods,
you might want to experiment with polishing pads. If
they develop the metal oxide films, you can always
peel the pad off and put on another one.

Good luck, and thanks for sharing the progress.
However, I doubt I will want to imitate your
experiments.

Guy

--- Anthony Stillman <atmer@flash.net> wrote:
> I've sanded the 64 mm speculum metal blank into
> shape.  Hogging with 60
> grit sandpaper, I worked my way up to 1500 grit. 
> The last few sanding
> steps I did at the Chabot Mirror Making Workshop. 
> To do a quick test, I
> polished the mirror with a paper towel, my finger
> and cerium. Instructive,
> but disappointing.  The light focused and the figure
> was, well it was.
> 
> To actually polish the mirror, I made a pitch lap
> with recycled 73,
> softened with a little bee's wax.  I polished with
> cerium, and immediately
> ran into a problem.  A film of copper colored metal
> built up on the lap.
> After this happened the feel of the polishing action
> changed.  Like there
> was grit in the slurry.  Examining the lap, I
> noticed scratches through the
> metal film and pitch.  I kept polishing.  Soon there
> were scratches on the
> mirror too.  I scraped the lap, warm pressed it, and
> started in again, but
> with rouge.  It took longer for the metal film to
> develop, but it did.
> After four more scrapes and presses I started
> looking for another solution.
> Eventually I tried rubbing the lap with bar soap,
> and presto change-o, the
> scratch problem went away.  The metal film still
> builds up on the lap, but
> there is less of it. I have to re-soap ever ten
> minutes or so.
> 
> It's taken quite a while to polish this little
> mirror and it's not done
> yet.  Probably in part this is due to my using
> rouge. I've yet to try
> cerium on a soaped lap.  I'll court that failure
> with the next mirror.


=====
Guy  BrandenburgWashington, DChttp://home.earthlink.net/~gfbranden/GFB_Home_Page.html

__________________________________
Do you Yahoo!?
Yahoo! Finance: Get your refund fast by filing online.
http://taxes.yahoo.com/filing.html